Chapter 20. Basic Networking

Contents

20.1. IP Addresses and Routing
20.2. IPv6—The Next Generation Internet
20.3. Name Resolution
20.4. Configuring a Network Connection with YaST
20.5. NetworkManager
20.6. Configuring a Network Connection Manually
20.7. smpppd as Dial-up Assistant

Abstract

Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card, modem or other device can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.

Linux and other Unix operating systems use the TCP/IP protocol. It is not a single network protocol, but a family of network protocols that offer various services. The protocols listed in Table 20.1, “Several Protocols in the TCP/IP Protocol Family”, are provided for the purpose of exchanging data between two machines via TCP/IP. Networks combined by TCP/IP, comprising a worldwide network, are also referred to as the Internet.

RFC stands for Request for Comments. RFCs are documents that describe various Internet protocols and implementation procedures for the operating system and its applications. The RFC documents describe the setup of Internet protocols. To expand your knowledge of any of the protocols, refer to the appropriate RFC documents. These are available at http://www.ietf.org/rfc.html.

Table 20.1. Several Protocols in the TCP/IP Protocol Family

Protocol

Description

TCP

Transmission Control Protocol: a connection-oriented secure protocol. The data to transmit is first sent by the application as a stream of data and converted into the appropriate format by the operating system. The data arrives at the respective application on the destination host in the original data stream format it was initially sent. TCP determines whether any data has been lost or jumbled during the transmission. TCP is implemented wherever the data sequence matters.

UDP

User Datagram Protocol: a connectionless, insecure protocol. The data to transmit is sent in the form of packets generated by the application. The order in which the data arrives at the recipient is not guaranteed and data loss is possible. UDP is suitable for record-oriented applications. It features a smaller latency period than TCP.

ICMP

Internet Control Message Protocol: Essentially, this is not a protocol for the end user, but a special control protocol that issues error reports and can control the behavior of machines participating in TCP/IP data transfer. In addition, it provides a special echo mode that can be viewed using the program ping.

IGMP

Internet Group Management Protocol: This protocol controls machine behavior when implementing IP multicast.


As shown in Figure 20.1, “Simplified Layer Model for TCP/IP”, data exchange takes place in different layers. The actual network layer is the insecure data transfer via IP (Internet protocol). On top of IP, TCP (transmission control protocol) guarantees, to a certain extent, security of the data transfer. The IP layer is supported by the underlying hardware-dependent protocol, such as ethernet.

Figure 20.1. Simplified Layer Model for TCP/IP

Simplified Layer Model for TCP/IP

The diagram provides one or two examples for each layer. The layers are ordered according to abstraction levels. The lowest layer is very close to the hardware. The uppermost layer, however, is almost a complete abstraction from the hardware. Every layer has its own special function. The special functions of each layer are mostly implicit in their description. The data link and physical layers represent the physical network used, such as ethernet.

Almost all hardware protocols work on a packet-oriented basis. The data to transmit is collected into packets (it cannot be sent all at once). The maximum size of a TCP/IP packet is approximately 64 KB. Packets are normally quite smaller, as the network hardware can be a limiting factor. The maximum size of a data packet on an ethernet is about fifteen hundred bytes. The size of a TCP/IP packet is limited to this amount when the data is sent over an ethernet. If more data is transferred, more data packets need to be sent by the operating system.

For the layers to serve their designated functions, additional information regarding each layer must be saved in the data packet. This takes place in the header of the packet. Every layer attaches a small block of data, called the protocol header, to the front of each emerging packet. A sample TCP/IP data packet traveling over an ethernet cable is illustrated in Figure 20.2, “TCP/IP Ethernet Packet”. The proof sum is located at the end of the packet, not at the beginning. This simplifies things for the network hardware.

Figure 20.2. TCP/IP Ethernet Packet

TCP/IP Ethernet Packet

When an application sends data over the network, the data passes through each layer, all implemented in the Linux kernel except the physical layer. Each layer is responsible for preparing the data so it can be passed to the next layer. The lowest layer is ultimately responsible for sending the data. The entire procedure is reversed when data is received. Like the layers of an onion, in each layer the protocol headers are removed from the transported data. Finally, the transport layer is responsible for making the data available for use by the applications at the destination. In this manner, one layer only communicates with the layer directly above or below it. For applications, it is irrelevant whether data is transmitted via a 100 Mbit/s FDDI network or via a 56-Kbit/s modem line. Likewise, it is irrelevant for the data line which kind of data is transmitted, as long as packets are in the correct format.

20.1. IP Addresses and Routing

The discussion in this section is limited to IPv4 networks. For information about IPv6 protocol, the successor to IPv4, refer to Section 20.2, “IPv6—The Next Generation Internet”.

20.1.1. IP Addresses

Every computer on the Internet has a unique 32-bit address. These 32 bits (or 4 bytes) are normally written as illustrated in the second row in Example 20.1, “Writing IP Addresses”.

Example 20.1. Writing IP Addresses

IP Address (binary):  11000000 10101000 00000000 00010100
IP Address (decimal):      192.     168.       0.      20

In decimal form, the four bytes are written in the decimal number system, separated by periods. The IP address is assigned to a host or a network interface. It can be used only once throughout the world. There are exceptions to this rule, but these are not relevant to the following passages.

The points in IP addresses indicate the hierarchical system. Until the 1990s, IP addresses were strictly categorized in classes. However, this system proved too inflexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used.

20.1.2. Netmasks and Routing

Netmasks are used to define the address range of a subnetwork. If two hosts are in the same subnetwork, they can reach each other directly. If they are not in the same subnetwork, they need the address of a gateway that handles all the traffic for the subnetwork. To check if two IP addresses are in the same subnet, simply AND both addresses with the netmask. If the result is identical, both IP addresses are in the same local network. If there are differences, the remote IP address, and thus the remote interface, can only be reached over a gateway.

To understand how the netmask works, look at Example 20.2, “Linking IP Addresses to the Netmask”. The netmask consists of 32 bits that identify how much of an IP address belongs to the network. All those bits that are 1 mark the corresponding bit in the IP address as belonging to the network. All bits that are 0 mark bits inside the subnetwork. This means that the more bits are 1, the smaller the subnetwork is. Because the netmask always consists of several successive 1 bits, it is also possible to just count the number of bits in the netmask. In Example 20.2, “Linking IP Addresses to the Netmask” the first net with 24 bits could also be written as 192.168.0.0/24.

Example 20.2. Linking IP Addresses to the Netmask

IP address (192.168.0.20):  11000000 10101000 00000000 00010100
Netmask   (255.255.255.0):  11111111 11111111 11111111 00000000
---------------------------------------------------------------
Result of the link:         11000000 10101000 00000000 00000000
In the decimal system:           192.     168.       0.       0

IP address (213.95.15.200): 11010101 10111111 00001111 11001000
Netmask    (255.255.255.0): 11111111 11111111 11111111 00000000
---------------------------------------------------------------
Result of the link:         11010101 10111111 00001111 00000000
In the decimal system:           213.      95.      15.       0

To give another example: all machines connected with the same ethernet cable are usually located in the same subnetwork and are directly accessible. Even when the subnet is physically divided by switches or bridges, these hosts can still be reached directly.

IP addresses outside the local subnet can only be reached if a gateway is configured for the target network. In the most common case, there is only one gateway that handles all traffic that is external. However, it is also possible to configure several gateways for different subnets.

If a gateway has been configured, all external IP packets are sent to the appropriate gateway. This gateway then attempts to forward the packets in the same manner—from host to host—until it reaches the destination host or the packet's TTL (time to live) expires.

Table 20.2. Specific Addresses

Address Type

Description

Base Network Address

This is the netmask AND any address in the network, as shown in Example 20.2, “Linking IP Addresses to the Netmask” under Result. This address cannot be assigned to any hosts.

Broadcast Address

This basically says, Access all hosts in this subnetwork. To generate this, the netmask is inverted in binary form and linked to the base network address with a logical OR. The above example therefore results in 192.168.0.255. This address cannot be assigned to any hosts.

Local Host

The address 127.0.0.1 is assigned to the loopback device on each host. A connection can be set up to your own machine with this address and with all addresses from the complete 127.0.0.0/8 loopback network as defined with IPv4. With IPv6 there is just one loopback address (::1).


Because IP addresses must be unique all over the world, you cannot just select random addresses. There are three address domains to use if you want to set up a private IP-based network. These cannot get any connection from the rest of the Internet, because they cannot be transmitted over the Internet. These address domains are specified in RFC 1597 and listed in Table 20.3, “Private IP Address Domains”.

Table 20.3. Private IP Address Domains

Network/Netmask

Domain

10.0.0.0/255.0.0.0

10.x.x.x

172.16.0.0/255.240.0.0

172.16.x.x172.31.x.x

192.168.0.0/255.255.0.0

192.168.x.x


20.2. IPv6—The Next Generation Internet

[Important]IBM System z: IPv6 Support

IPv6 is not supported by the CTC and IUCV network connections of the IBM System z hardware.

Due to the emergence of the WWW (World Wide Web), the Internet has experienced explosive growth, with an increasing number of computers communicating via TCP/IP in the past fifteen years. Since Tim Berners-Lee at CERN (http://public.web.cern.ch) invented the WWW in 1990, the number of Internet hosts has grown from a few thousand to about a hundred million.

As mentioned, an IPv4 address consists of only 32 bits. Also, quite a few IP addresses are lost—they cannot be used due to the way in which networks are organized. The number of addresses available in your subnet is two to the power of the number of bits, minus two. A subnetwork has, for example, 2, 6, or 14 addresses available. To connect 128 hosts to the Internet, for example, you need a subnetwork with 256 IP addresses, from which only 254 are usable, because two IP addresses are needed for the structure of the subnetwork itself: the broadcast and the base network address.

Under the current IPv4 protocol, DHCP or NAT (network address translation) are the typical mechanisms used to circumvent the potential address shortage. Combined with the convention to keep private and public address spaces separate, these methods can certainly mitigate the shortage. The problem with them lies in their configuration, which is a chore to set up and a burden to maintain. To set up a host in an IPv4 network, you need a number of address items, such as the host's own IP address, the subnetmask, the gateway address and maybe a name server address. All these items need to be known and cannot be derived from somewhere else.

With IPv6, both the address shortage and the complicated configuration should be a thing of the past. The following sections tell more about the improvements and benefits brought by IPv6 and about the transition from the old protocol to the new one.

20.2.1. Advantages

The most important and most visible improvement brought by the new protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses.

However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong. More details about this are found in Section 20.2.2, “Address Types and Structure”.

The following is a list of some other advantages of the new protocol:

Autoconfiguration

IPv6 makes the network plug and play capable, which means that a newly set up system integrates into the (local) network without any manual configuration. The new host uses its automatic configuration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor discovery (ND) protocol. This method does not require any intervention on the administrator's part and there is no need to maintain a central server for address allocation—an additional advantage over IPv4, where automatic address allocation requires a DHCP server.

Nevertheless if a router is connected to a switch, the router should send periodic advertisments with flags telling the hosts of a network how they should interact with each other. For more information, see RFC 2462 and the radvd.conf(5) manpage, and RFC 3315.

Mobility

IPv6 makes it possible to assign several addresses to one network interface at the same time. This allows users to access several networks easily, something that could be compared with the international roaming services offered by mobile phone companies: when you take your mobile phone abroad, the phone automatically logs in to a foreign service as soon as it enters the corresponding area, so you can be reached under the same number everywhere and are able to place an outgoing call just like in your home area.

Secure Communication

With IPv4, network security is an add-on function. IPv6 includes IPsec as one of its core features, allowing systems to communicate over a secure tunnel to avoid eavesdropping by outsiders on the Internet.

Backward Compatibility

Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6 at one time. Therefore, it is crucial that both protocols are able to coexist not only on the Internet, but also on one system. This is ensured by compatible addresses (IPv4 addresses can easily be translated into IPv6 addresses) and through the use of a number of tunnels. See Section 20.2.3, “Coexistence of IPv4 and IPv6”. Also, systems can rely on a dual stack IP technique to support both protocols at the same time, meaning that they have two network stacks that are completely separate, such that there is no interference between the two protocol versions.

Custom Tailored Services through Multicasting

With IPv4, some services, such as SMB, need to broadcast their packets to all hosts in the local network. IPv6 allows a much more fine-grained approach by enabling servers to address hosts through multicasting—by addressing a number of hosts as parts of a group (which is different from addressing all hosts through broadcasting or each host individually through unicasting). Which hosts are addressed as a group may depend on the concrete application. There are some predefined groups to address all name servers (the all name servers multicast group), for example, or all routers (the all routers multicast group).

20.2.2. Address Types and Structure

As mentioned, the current IP protocol is lacking in two important aspects: there is an increasing shortage of IP addresses and configuring the network and maintaining the routing tables is becoming a more complex and burdensome task. IPv6 solves the first problem by expanding the address space to 128 bits. The second one is countered by introducing a hierarchical address structure, combined with sophisticated techniques to allocate network addresses, as well as multihoming (the ability to assign several addresses to one device, giving access to several networks).

When dealing with IPv6, it is useful to know about three different types of addresses:

Unicast

Addresses of this type are associated with exactly one network interface. Packets with such an address are delivered to only one destination. Accordingly, unicast addresses are used to transfer packets to individual hosts on the local network or the Internet.

Multicast

Addresses of this type relate to a group of network interfaces. Packets with such an address are delivered to all destinations that belong to the group. Multicast addresses are mainly used by certain network services to communicate with certain groups of hosts in a well-directed manner.

Anycast

Addresses of this type are related to a group of interfaces. Packets with such an address are delivered to the member of the group that is closest to the sender, according to the principles of the underlying routing protocol. Anycast addresses are used to make it easier for hosts to find out about servers offering certain services in the given network area. All servers of the same type have the same anycast address. Whenever a host requests a service, it receives a reply from the server with the closest location, as determined by the routing protocol. If this server should fail for some reason, the protocol automatically selects the second closest server, then the third one, and so forth.

An IPv6 address is made up of eight four-digit fields, each representing 16 bits, written in hexadecimal notation. They are separated by colons (:). Any leading zero bytes within a given field may be dropped, but zeros within the field or at its end may not. Another convention is that more than four consecutive zero bytes may be collapsed into a double colon. However, only one such :: is allowed per address. This kind of shorthand notation is shown in Example 20.3, “Sample IPv6 Address”, where all three lines represent the same address.

Example 20.3. Sample IPv6 Address

fe80 : 0000 : 0000 : 0000 : 0000 : 10 : 1000 : 1a4
fe80 :    0 :    0 :    0 :    0 : 10 : 1000 : 1a4
fe80 :                           : 10 : 1000 : 1a4

Each part of an IPv6 address has a defined function. The first bytes form the prefix and specify the type of address. The center part is the network portion of the address, but it may be unused. The end of the address forms the host part. With IPv6, the netmask is defined by indicating the length of the prefix after a slash at the end of the address. An address, as shown in Example 20.4, “IPv6 Address Specifying the Prefix Length”, contains the information that the first 64 bits form the network part of the address and the last 64 form its host part. In other words, the 64 means that the netmask is filled with 64 1-bit values from the left. Just like with IPv4, the IP address is combined with AND with the values from the netmask to determine whether the host is located in the same subnetwork or in another one.

Example 20.4. IPv6 Address Specifying the Prefix Length

fe80::10:1000:1a4/64

IPv6 knows about several predefined types of prefixes. Some of these are shown in Table 20.4, “Various IPv6 Prefixes”.

Table 20.4. Various IPv6 Prefixes

Prefix (hex)

Definition

00

IPv4 addresses and IPv4 over IPv6 compatibility addresses. These are used to maintain compatibility with IPv4. Their use still requires a router able to translate IPv6 packets into IPv4 packets. Several special addresses, such as the one for the loopback device, have this prefix as well.

2 or 3 as the first digit

Aggregatable global unicast addresses. As is the case with IPv4, an interface can be assigned to form part of a certain subnetwork. Currently, there are the following address spaces: 2001::/16 (production quality address space) and 2002::/16 (6to4 address space).

fe80::/10

Link-local addresses. Addresses with this prefix should not be routed and should therefore only be reachable from within the same subnetwork.

fec0::/10

Site-local addresses. These may be routed, but only within the network of the organization to which they belong. In effect, they are the IPv6 equivalent of the current private network address space, such as 10.x.x.x.

ff

These are multicast addresses.


A unicast address consists of three basic components:

Public Topology

The first part (which also contains one of the prefixes mentioned above) is used to route packets through the public Internet. It includes information about the company or institution that provides the Internet access.

Site Topology

The second part contains routing information about the subnetwork to which to deliver the packet.

Interface ID

The third part identifies the interface to which to deliver the packet. This also allows for the MAC to form part of the address. Given that the MAC is a globally unique, fixed identifier coded into the device by the hardware maker, the configuration procedure is substantially simplified. In fact, the first 64 address bits are consolidated to form the EUI-64 token, with the last 48 bits taken from the MAC, and the remaining 24 bits containing special information about the token type. This also makes it possible to assign an EUI-64 token to interfaces that do not have a MAC, such as those based on PPP or ISDN.

On top of this basic structure, IPv6 distinguishes between five different types of unicast addresses:

:: (unspecified)

This address is used by the host as its source address when the interface is initialized for the first time—when the address cannot yet be determined by other means.

::1 (loopback)

The address of the loopback device.

IPv4 Compatible Addresses

The IPv6 address is formed by the IPv4 address and a prefix consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 20.2.3, “Coexistence of IPv4 and IPv6”) to allow IPv4 and IPv6 hosts to communicate with others operating in a pure IPv4 environment.

IPv4 Addresses Mapped to IPv6

This type of address specifies a pure IPv4 address in IPv6 notation.

Local Addresses

There are two address types for local use:

link-local

This type of address can only be used in the local subnetwork. Packets with a source or target address of this type should not be routed to the Internet or other subnetworks. These addresses contain a special prefix (fe80::/10) and the interface ID of the network card, with the middle part consisting of zero bytes. Addresses of this type are used during automatic configuration to communicate with other hosts belonging to the same subnetwork.

site-local

Packets with this type of address may be routed to other subnetworks, but not to the wider Internet—they must remain inside the organization's own network. Such addresses are used for intranets and are an equivalent of the private address space defined by IPv4. They contain a special prefix (fec0::/10), the interface ID, and a 16 bit field specifying the subnetwork ID. Again, the rest is filled with zero bytes.

As a completely new feature introduced with IPv6, each network interface normally gets several IP addresses, with the advantage that several networks can be accessed through the same interface. One of these networks can be configured completely automatically using the MAC and a known prefix with the result that all hosts on the local network can be reached as soon as IPv6 is enabled (using the link-local address). With the MAC forming part of it, any IP address used in the world is unique. The only variable parts of the address are those specifying the site topology and the public topology, depending on the actual network in which the host is currently operating.

For a host to go back and forth between different networks, it needs at least two addresses. One of them, the home address, not only contains the interface ID but also an identifier of the home network to which it normally belongs (and the corresponding prefix). The home address is a static address and, as such, it does not normally change. Still, all packets destined to the mobile host can be delivered to it, regardless of whether it operates in the home network or somewhere outside. This is made possible by the completely new features introduced with IPv6, such as stateless autoconfiguration and neighbor discovery. In addition to its home address, a mobile host gets one or more additional addresses that belong to the foreign networks where it is roaming. These are called care-of addresses. The home network has a facility that forwards any packets destined to the host when it is roaming outside. In an IPv6 environment, this task is performed by the home agent, which takes all packets destined to the home address and relays them through a tunnel. On the other hand, those packets destined to the care-of address are directly transferred to the mobile host without any special detours.

20.2.3. Coexistence of IPv4 and IPv6

The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual process. Both protocols will coexist for some time to come. The coexistence on one system is guaranteed where there is a dual stack implementation of both protocols. That still leaves the question of how an IPv6 enabled host should communicate with an IPv4 host and how IPv6 packets should be transported by the current networks, which are predominantly IPv4 based. The best solutions offer tunneling and compatibility addresses (see Section 20.2.2, “Address Types and Structure”).

IPv6 hosts that are more or less isolated in the (worldwide) IPv4 network can communicate through tunnels: IPv6 packets are encapsulated as IPv4 packets to move them across an IPv4 network. Such a connection between two IPv4 hosts is called a tunnel. To achieve this, packets must include the IPv6 destination address (or the corresponding prefix) as well as the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be configured manually according to an agreement between the hosts' administrators. This is also called static tunneling.

However, the configuration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three different methods of dynamic tunneling:

6over4

IPv6 packets are automatically encapsulated as IPv4 packets and sent over an IPv4 network capable of multicasting. IPv6 is tricked into seeing the whole network (Internet) as a huge local area network (LAN). This makes it possible to determine the receiving end of the IPv4 tunnel automatically. However, this method does not scale very well and is also hampered by the fact that IP multicasting is far from widespread on the Internet. Therefore, it only provides a solution for smaller corporate or institutional networks where multicasting can be enabled. The specifications for this method are laid down in RFC 2529.

6to4

With this method, IPv4 addresses are automatically generated from IPv6 addresses, enabling isolated IPv6 hosts to communicate over an IPv4 network. However, a number of problems have been reported regarding the communication between those isolated IPv6 hosts and the Internet. The method is described in RFC 3056.

IPv6 Tunnel Broker

This method relies on special servers that provide dedicated tunnels for IPv6 hosts. It is described in RFC 3053.

20.2.4. Configuring IPv6

To configure IPv6, you normally do not need to make any changes on the individual workstations. IPv6 is enabled by default. You can disable it during installation in the network configuration step described in Section “Network Configuration” (Chapter 6, Installation with YaST, ↑Deployment Guide). To disable or enable IPv6 on an installed system, use the YaST Network Settings module. On the Global Options tab, check or uncheck the Enable IPv6 option as necessary. If you want to enable it temporarily until the next reboot, enter modprobe -i ipv6 as root. It is basically impossible to unload the ipv6 module once loaded.

Because of the autoconfiguration concept of IPv6, the network card is assigned an address in the link-local network. Normally, no routing table management takes place on a workstation. The network routers can be queried by the workstation, using the router advertisement protocol, for what prefix and gateways should be implemented. The radvd program can be used to set up an IPv6 router. This program informs the workstations which prefix to use for the IPv6 addresses and which routers. Alternatively, use zebra/quagga for automatic configuration of both addresses and routing.

Consult the ifcfg-tunnel (5) man page to get information about how to set up various types of tunnels using the /etc/sysconfig/network files.

20.2.5. For More Information

The above overview does not cover the topic of IPv6 comprehensively. For a more in-depth look at the new protocol, refer to the following online documentation and books:

http://www.ipv6.org/

The starting point for everything about IPv6.

http://www.ipv6day.org

All information needed to start your own IPv6 network.

http://www.ipv6-to-standard.org/

The list of IPv6-enabled products.

http://www.bieringer.de/linux/IPv6/

Here, find the Linux IPv6-HOWTO and many links related to the topic.

RFC 2640

The fundamental RFC about IPv6.

IPv6 Essentials

A book describing all the important aspects of the topic is IPv6 Essentials by Silvia Hagen (ISBN 0-596-00125-8).

20.3. Name Resolution

DNS assists in assigning an IP address to one or more names and assigning a name to an IP address. In Linux, this conversion is usually carried out by a special type of software known as bind. The machine that takes care of this conversion is called a name server. The names make up a hierarchical system in which each name component is separated by a period. The name hierarchy is, however, independent of the IP address hierarchy described above.

Consider a complete name, such as jupiter.example.com, written in the format hostname.domain. A full name, referred to as a fully qualified domain name (FQDN), consists of a hostname and a domain name (example.com). The latter also includes the top level domain or TLD (com).

TLD assignment has become quite confusing for historical reasons. Traditionally, three-letter domain names are used in the USA. In the rest of the world, the two-letter ISO national codes are the standard. In addition to that, longer TLDs were introduced in 2000 that represent certain spheres of activity (for example, .info, .name, .museum).

In the early days of the Internet (before 1990), the file /etc/hosts was used to store the names of all the machines represented over the Internet. This quickly proved to be impractical in the face of the rapidly growing number of computers connected to the Internet. For this reason, a decentralized database was developed to store the hostnames in a widely distributed manner. This database, similar to the name server, does not have the data pertaining to all hosts in the Internet readily available, but can dispatch requests to other name servers.

The top of the hierarchy is occupied by root name servers. These root name servers manage the top level domains and are run by the Network Information Center (NIC). Each root name server knows about the name servers responsible for a given top level domain. Information about top level domain NICs is available at http://www.internic.net.

DNS can do more than just resolve hostnames. The name server also knows which host is receiving e-mails for an entire domain—the mail exchanger (MX).

For your machine to resolve an IP address, it must know about at least one name server and its IP address. Easily specify such a name server with the help of YaST. If you have a modem dial-up connection, you may not need to configure a name server manually at all. The dial-up protocol provides the name server address as the connection is made. The configuration of name server access with SUSE® Linux Enterprise Server is described in Section 20.4.1.4, “Configuring Hostname and DNS”. Setting up your own name server is described in Chapter 23, The Domain Name System.

The protocol whois is closely related to DNS. With this program, quickly find out who is responsible for any given domain.

[Note]MDNS and .local Domain Names

The .local top level domain is treated as link-local domain by the resolver. DNS requests are send as multicast DNS requests instead of normal DNS requests. If you already use the .local domain in your nameserver configuration, you must switch this option off in /etc/host.conf. For more information, see the host.conf manual page.

If you want to switch off MDNS during installation, use nomdns=1 as a boot parameter.

For more information on multicast DNS, see http://www.multicastdns.org.

20.4. Configuring a Network Connection with YaST

There are many supported networking types on Linux. Most of them use different device names and the configuration files are spread over several locations in the file system. For a detailed overview of the aspects of manual network configuration, see Section 20.6, “Configuring a Network Connection Manually”.

On SUSE Linux Enterprise Desktop, where NetworkManager is active by default, all network cards are configured. If NetworkManager is not active, only the first interface with link up (with a network cable connected) is automatically configured. Additional hardware can be configured any time on the installed system. The following sections describe the network configuration for all types of network connections supported by SUSE Linux Enterprise Server.

[Tip]IBM System z: Hotpluggable Network Cards

On IBM System z platforms, hotpluggable network cards are supported, but not their automatic network integration via DHCP (as is the case on the PC). After detection, manually configure the interface.

20.4.1. Configuring the Network Card with YaST

To configure your wired or wireless network card in YaST, select Network Devices+Network Settings. After starting the module, YaST displays the Network Settings dialog with four tabs: Global Options, Overview, Hostname/DNS and Routing.

The Global Options tab allows you to set general networking options such as the use of NetworkManager, IPv6 and general DHCP options. For more information, see Section 20.4.1.1, “Configuring Global Networking Options”.

The Overview tab contains information about installed network interfaces and configurations. Any properly detected network card is listed with its name. You can manually configure new cards, remove or change their configuration in this dialog. If you want to manually configure a card that was not automatically detected, see Section 20.4.1.3, “Configuring an Undetected Network Card”. If you want to change the configuration of an already configured card, see Section 20.4.1.2, “Changing the Configuration of a Network Card”.

The Hostname/DNS tab allows to set the hostname of the machine and name the servers to be used. For more information, see Section 20.4.1.4, “Configuring Hostname and DNS”.

The Routing tab is used for the configuration of routing. See Section 20.4.1.5, “Configuring Routing” for more information.

Figure 20.3. Configuring Network Settings

Configuring Network Settings

20.4.1.1. Configuring Global Networking Options

The Global Options tab of the YaST Network Settings module allows you to set important global networking options, such as the use of NetworkManager, IPv6 and DHCP client options. These settings are applicable for all network interfaces.

In the Network Setup Method choose the way network connections are managed. If you want a NetworkManager desktop applet to manage connections for all interfaces, choose User Controlled with NetworkManager. This option is well suited for switching between multiple wired and wireless networks. If you do not run a desktop environment (GNOME or KDE), or if your computer is a Xen server, virtual system, or provides network services such as DHCP or DNS in your network, use the Traditional Method with ifup. If NetworkManager is used, nm-applet should be used to configure network options and the Overview, Hostname/DNS and Routing tabs of the Network Settings module are disabled. For more information on NetworkManager, see Chapter 25, Using NetworkManager.

In the IPv6 Protocol Settings choose whether you want to use the IPv6 protocol. It is possible to use IPv6 together with IPv4. By default, IPv6 is activated. However, in networks not using IPv6 protocol, response times can be faster with IPv6 protocol disabled. If you want to disable IPv6, uncheck the Enable IPv6 option. This disables autoload of the kernel module for IPv6. This will be applied after reboot.

In the DHCP Client Options configure options for the DHCP client. If you want the DHCP client to ask the server to always broadcast its responses, check Request Broadcast Response. It may be needed if your machine is moving between different networks. The DHCP Client Identifier must be different for each DHCP client on a single network. If left empty, it defaults to the hardware address of the network interface. However, if you are running several virtual machines using the same network interface and, therefore, the same hardware address, specify a unique free-form identifier here.

The Hostname to Send specifies a string used for the hostname option field when dhcpcd sends messages to DHCP server. Some DHCP servers update name server zones (forward and reverse records) according to this hostname (Dynamic DNS). Also, some DHCP servers require the Hostname to Send option field to contain a specific string in the DHCP messages from clients. Leave AUTO to send the current hostname (that is the one defined in /etc/HOSTNAME). Leave the option field empty for not sending any hostname. If yo do not want to change the default route according to the information from DHCP, uncheck Change Default Route via DHCP.

20.4.1.2. Changing the Configuration of a Network Card

To change the configuration of a network card, select a card from the list of the detected cards in Network Settings+Overview in YaST and click Edit. The Network Card Setup dialog appears in which to adjust the card configuration using the General, Address and Hardware tabs. For information about wireless card configuration, see Section 17.5, “Configuration with YaST”.

20.4.1.2.1. Configuring IP Addresses

You can set the IP address of the network card or the way its IP address is determined in the Address tab of the Network Card Setup dialog. Both IPv4 and IPv6 addresses are supported. The network card can have No IP Address (which is useful for bonding devices), a Statically Assigned IP Address (IPv4 or IPv6) or a Dynamic Address assigned via DHCP or Zeroconf or both.

If using Dynamic Address, select whether to use DHCP Version 4 Only (for IPv4), DHCP Version 6 Only (for IPv6) or DHCP Both Version 4 and 6.

If possible, the first network card with link that is available during the installation is automatically configured to use automatic address setup via DHCP. On SUSE Linux Enterprise Desktop, where NetworkManager is active by default, all network cards are configured.

[Note]IBM System z and DHCP

On IBM System z platforms, DHCP-based address configuration is only supported with network cards that have a MAC address. This is only the case with OSA and OSA Express cards.

DHCP should also be used if you are using a DSL line but with no static IP assigned by the ISP (Internet Service Provider). If you decide to use DHCP, configure the details in DHCP Client Options in the Global Options tab of the Network Settings dialog of the YaST network card configuration module. Specify whether the DHCP client should ask the server to always broadcast its responses in Request Broadcast Response. This option may be needed if your machine is a mobile client moving between networks. If you have a virtual host setup where different hosts communicate through the same interface, an DHCP Client Identifier is necessary to distinguish them.

DHCP is a good choice for client configuration but it is not ideal for server configuration. To set a static IP address, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST network card configuration module and click Edit.

  2. In the Address tab, choose Statically Assigned IP Address.

  3. Enter the IP Address. Both IPv4 and IPv6 addresses can be used. Enter the network mask in Subnet Mask. If the IPv6 address is used, use Subnet Mask for prefix length in format /64.

    Optionally, you can enter a fully qualified Hostname for this address, which will be written to the /etc/hosts configuration file.

  4. Click Next.

  5. To activate the configuration, click OK.

If you use the static address, the name servers and default gateway are not configured automatically. To configure name servers, proceed as described in Section 20.4.1.4, “Configuring Hostname and DNS”. To configure a gateway, proceed as described in Section 20.4.1.5, “Configuring Routing”.

20.4.1.2.2. Configuring Aliases

One network device can have multiple IP addresses, called aliases.

[Note]Aliases Are a Compatibility Feature

These so-called aliases resp. labels work with IPv4 only. With IPv6 they will be ignored. Using iproute2 network interfaces can have one or more addresses.

Using YaST to set an alias for your network card, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST network card configuration module and click Edit.

  2. In the Address+Additional Addresses tab, click Add.

  3. Enter Alias Name, IP Address, and Netmask. Do not include the interface name in the alias name.

  4. Click OK.

  5. Click Next.

  6. To activate the configuration, click OK.

20.4.1.2.3. Changing the Device Name and Udev Rules

It is possible to change the device name of the network card when it is used. It is also possible to determine whether the network card should be identified by udev via its hardware (MAC) address or via the bus ID. The later option is preferable in large servers to ease hot swapping of cards. To set these options with YaST, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings module and click Edit.

  2. Go to the Hardware tab. The current device name is shown in Udev Rules. Click Change.

  3. Select whether udev should identify the card by its MAC Address or Bus ID. The current MAC address and bus ID of the card are shown in the dialog.

  4. To change the device name, check the Change Device Name option and edit the name.

  5. Click OK and Next.

  6. To activate the configuration, click OK.

20.4.1.2.4. Changing Network Card Kernel Driver

For some network cards, several kernel drivers may be available. If the card is already configured, YaST allows you to select a kernel driver to be used from a list of available suitable drivers. It is also possible to specify options for the kernel driver. To set these options with YaST, proceed as follows:

  1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings module and click Edit.

  2. Go to the Hardware tab.

  3. Select the kernel driver to be used in Module Name. Enter any options for the selected driver in Options in the form option=value . If more options are used, they should be space-separated.

  4. Click OK and Next.

  5. To activate the configuration, click OK.

20.4.1.2.5. Activating the Network Device

If you use the traditional method with ifup, you can configure your device to either start during boot, on cable connection, on card detection, manually or never. To change device start-up, proceed as follows:

  1. In YaST select a card from the list of detected cards in Network Devices+Network Settings and click Edit.

  2. In the General tab, select the desired entry from Device Activation.

    Choose At Boot Time to start the device during the system boot. With On Cable Connection, the interface is watched for any existing physical connection. With On Hotplug, the interface is set as soon as available. It is similar to the At Boot Time option, and only differs in the fact that no error occurs if the interface is not present at boot time. Choose Manually to control the interface manually with ifup. Choose Never to not start the device at all. The On NFSroot is similar to At Boot Time, but the interface does not shut down with the rcnetwork stop command. Use this if you use an nfs or iscsi root file system.

  3. Click Next.

  4. To activate the configuration, click OK.

Usually, only the system administrator can activate and deactivate network interfaces. If you want any user to be able to activate this interface via KInternet, select Enable Device Control for Non-root User via KInternet.

20.4.1.2.6. Setting Up Maximum Transfer Unit Size

You can set a maximum transmission unit (MTU) for the interface. MTU refers to the largest allowed packet size in bytes. A higher MTU brings higher bandwidth efficiency. However, large packets can block up a slow interface for some time, increasing the lag for further packets.

  1. In YaST select a card from the list of detected cards in Network Devices+Network Settings and click Edit.

  2. In the General tab, select the desired entry from the Set MTU list.

  3. Click Next.

  4. To activate the configuration, click OK.

20.4.1.2.7. Configuring the Firewall

Without having to enter the detailed firewall setup as described in Section “Configuring the Firewall with YaST” (Chapter 15, Masquerading and Firewalls, ↑Security Guide), you can determine the basic firewall setup for your device as part of the device setup. Proceed as follows:

  1. Open the YaST Network Devices+Network Settings module. In the Overview tab, select a card from the list of detected cards and click Edit.

  2. Enter the General tab of the Network Settings dialog.

  3. Determine the firewall zone to which your interface should be assigned. The following options are available:

    Firewall Disabled

    This option is available only if the firewall is disabled and the firewall does not run at all. Only use this option if your machine is part of a greater network that is protected by an outer firewall.

    Automatically Assign Zone

    This option is available only if the firewall is enabled. The firewall is running and the interface is automatically assigned to a firewall zone. The zone which contains the keyword any or the external zone will be used for such an interface.

    Internal Zone (Unprotected)

    The firewall is running, but does not enforce any rules to protect this interface. Use this option if your machine is part of a greater network that is protected by an outer firewall. It is also useful for the interfaces connected to the internal network, when the machine has more network interfaces.

    Demilitarized Zone

    A demilitarized zone is an additional line of defense in front of an internal network and the (hostile) Internet. Hosts assigned to this zone can be reached from the internal network and from the Internet, but cannot access the internal network.

    External Zone

    The firewall is running on this interface and fully protects it against other—presumably hostile—network traffic. This is the default option.

  4. Click Next.

  5. Activate the configuration by clicking OK.

20.4.1.3. Configuring an Undetected Network Card

Your card may not be detected correctly. In this case, the card is not included in the list of detected cards. If you are sure that your system includes a driver for your card, you can configure it manually. You can also configure special network device types, such as bridge, bond, TUN or TAP. To configure an undetected network card (or a special device) proceed as follows:

  1. In the Network Devices+Network Settings+Overview dialog in YaST click Add.

  2. In the Hardware dialog, set the Device Type of the interface from the available options and Configuration Name. If the network card is a PCMCIA or USB device, activate the respective check box and exit this dialog with Next. Otherwise, you can define the kernel Module Name to be used for the card and its Options, if necessary.

    In Ethtool Options, you can set ethtool options used by ifup for the interface. See the ethtool manual page for available options. If the option string starts with a - (for example -K interface_name rx on), the second word in the string is replaced with the current interface name. Otherwise (for example autoneg off speed 10) ifup prepends -s interface_name.

  3. Click Next.

  4. Configure any needed options, such as the IP address, device activation or firewall zone for the interface in the General, Address, and Hardware tabs. For more information about the configuration options, see Section 20.4.1.2, “Changing the Configuration of a Network Card”.

  5. If you selected Wireless as the device type of the interface, configure the wireless connection in the next dialog. Detailed information about wireless device configuration is available in Chapter 17, Wireless LAN.

  6. Click Next.

  7. To activate the new network configuration, click OK.

20.4.1.4. Configuring Hostname and DNS

If you did not change the network configuration during installation and the wired card was already available, a hostname was automatically generated for your computer and DHCP was activated. The same applies to the name service information your host needs to integrate into a network environment. If DHCP is used for network address setup, the list of domain name servers is automatically filled with the appropriate data. If a static setup is preferred, set these values manually.

To change the name of your computer and adjust the name server search list, proceed as follows:

  1. Go to the Network Settings+Hostname/DNS tab in the Network Devices module in YaST.

  2. Enter the Hostname and, if needed, the Domain Name. The domain is especially important if the machine is a mail server. Note that the hostname is global and applies to all set network interfaces.

    If you are using DHCP to get an IP address, the hostname of your computer will be automatically set by the DHCP. You may want to disable this behavior if you connect to different networks, because they may assign different hostnames and changing the hostname at runtime may confuse the graphical desktop. To disable using DHCP to get an IP address uncheck Change Hostname via DHCP.

    Assign Hostname to Loopback IP associates your hostname with 127.0.0.2 (loopback) IP address in /etc/hosts. This is an useful option if you want to have the hostname resolvable at all times, even without active network.

  3. In Modify DNS Configuration, select the way the DNS configuration (name servers, search list, the content of the /etc/resolv.conf file) is modified.

    If the Use Default Policy option is selected, the configuration is handled by the netconfig script which merges the data defined statically (with YaST or in the configuration files) with data obtained dynamically (from the DHCP client or NetworkManager). This default policy is sufficient in most cases.

    If the Only Manually option is selected, netconfig is not allowed to modify the /etc/resolv.conf file. However, this file can be edited manually.

    If the Custom Policy option is selected, a Custom Policy Rule string defining the merge policy should be specified. The string consists of a comma-separated list of interface names to be considered a valid source of settings. Except for complete interface names, basic wildcards to match multiple interfaces are allowed, as well. For example, eth* ppp? will first target all eth and then all ppp0-ppp9 interfaces. There are two special policy values that indicate how to apply the static settings defined in the /etc/sysconfig/network/config file:

    STATIC

    The static settings have to be merged together with the dynamic settings.

    STATIC_FALLBACK

    The static settings are used only when no dynamic configuration is available.

    For more information, see the man 8 netconfig.

  4. Enter the Name Servers and fill in the Domain Search list. Name servers must be specified by IP addresses, such as 192.168.1.116, not by hostnames. Names specified in the Domain Search tab are domain names used for resolving hostnames without a specified domain. If more than one Domain Search is used, separate domains with commas or white space.

  5. To activate the configuration, click OK.

20.4.1.5. Configuring Routing

To make your machine communicate with other machines and other networks, routing information must be given to make network traffic take the correct path. If DHCP is used, this information is automatically provided. If a static setup is used, this data must be added manually.

  1. In YaST go to Network Settings+Routing.

  2. Enter the IP address of the Default Gateway (IPv4 and IPv6 if necessary). The default gateway matches every possible destination, but if any other entry exists that matches the required address, use this instead of the default route.

  3. More entries can be entered in the Routing Table. Enter the Destination network IP address, Gateway IP address and the Netmask. Select the Device through which the traffic to the defined network will be routed (the minus sign stands for any device). To omit any of these values, use the minus sign -. To enter a default gateway into the table, use default in the Destination field.

    [Note]

    If more default routes are used, it is possible to specify the metric option to determine which route has a higher priority. To specify the metric option, enter - metric number in Options. The route with the highest metric is used as default. If the network device is disconnected, its route will be removed and the next one will be used. However, the current kernel does not use metric in static routing, only routing daemons like multipathd do.

  4. If the system is a router, enable the IP Forwarding option in the Network Settings.

  5. To activate the configuration, click OK.

20.4.2. Modem

[Tip]IBM System z: Modem

The configuration of this type of hardware is not supported on IBM System z platforms.

In the YaST Control Center, access the modem configuration under Network Devices+Modem. If your modem was not automatically detected, go to the Modem Devices tab and open the dialog for manual configuration by clicking Add. Enter the interface to which the modem is connected under Modem Device.

[Tip]CDMA and GPRS Modems

Configure supported CDMA and GPRS modems with the YaST Modem module just as you would configure regular modems.

Figure 20.4. Modem Configuration

Modem Configuration

If you are behind a private branch exchange (PBX), you may need to enter a dial prefix. This is often a zero. Consult the instructions that came with the PBX to find out. Also select whether to use tone or pulse dialing, whether the speaker should be on and whether the modem should wait until it detects a dial tone. The last option should not be enabled if the modem is connected to an exchange.

Under Details, set the baud rate and the modem initialization strings. Only change these settings if your modem was not detected automatically or if it requires special settings for data transmission to work. This is mainly the case with ISDN terminal adapters. Leave this dialog by clicking OK. To delegate control over the modem to the normal user without root permissions, activate Enable Device Control for Non-root User via KInternet. In this way, a user without administrator permissions can activate or deactivate an interface. Under Dial Prefix Regular Expression, specify a regular expression. The Dial Prefix in KInternet, which can be modified by the normal user, must match this regular expression. If this field is left empty, the user cannot set a different Dial Prefix without administrator permissions.

In the next dialog, select the ISP. To choose from a predefined list of ISPs operating in your country, select Country. Alternatively, click New to open a dialog in which to provide the data for your ISP. This includes a name for the dial-up connection and ISP as well as the login and password provided by your ISP. Enable Always Ask for Password to be prompted for the password each time you connect.

In the last dialog, specify additional connection options:

Dial on Demand

If you enable Dial on Demand, set at least one name server. Use this feature only if your Internet connection is inexpensive, because there are programs that periodically request data from the Internet.

Modify DNS when Connected

This option is enabled by default, with the effect that the name server address is updated each time you connect to the Internet.

Automatically Retrieve DNS

If the provider does not transmit its domain name server after connecting, disable this option and enter the DNS data manually.

Automatically Reconnect

If this options is enabled, the connection is automatically reestablished after failure.

Ignore Prompts

This option disables the detection of any prompts from the dial-up server. If the connection build-up is slow or does not work at all, try this option.

External Firewall Interface

Selecting this option activates the firewall and sets the interface as external. This way, you are protected from outside attacks for the duration of your Internet connection.

Idle Time-Out (seconds)

With this option, specify a period of network inactivity after which the modem disconnects automatically.

IP Details

This opens the address configuration dialog. If your ISP does not assign a dynamic IP address to your host, disable Dynamic IP Address then enter your host's local IP address and the remote IP address. Ask your ISP for this information. Leave Default Route enabled and close the dialog by selecting OK.

Selecting Next returns to the original dialog, which displays a summary of the modem configuration. Close this dialog with OK.

20.4.3. ISDN

[Tip]IBM System z: ISDN

The configuration of this type of hardware is not supported on IBM System z platforms.

Use this module to configure one or several ISDN cards for your system. If YaST did not detect your ISDN card, click on Add in the ISDN Devices tab and manually select your card. Multiple interfaces are possible, but several ISPs can be configured for one interface. In the subsequent dialogs, set the ISDN options necessary for the proper functioning of the card.

Figure 20.5. ISDN Configuration

ISDN Configuration

In the next dialog, shown in Figure 20.5, “ISDN Configuration”, select the protocol to use. The default is Euro-ISDN (EDSS1), but for older or larger exchanges, select 1TR6. If you are in the US, select NI1. Select your country in the relevant field. The corresponding country code then appears in the field next to it. Finally, provide your Area Code and the Dial Prefix if necessary. If you do not want to log all your ISDN traffic, uncheck the Start ISDN Log option.

Activate Device defines how the ISDN interface should be started: At Boot Time causes the ISDN driver to be initialized each time the system boots. Manually requires you to load the ISDN driver as root with the command rcisdn start. On Hotplug, used for PCMCIA or USB devices, loads the driver after the device is plugged in. When finished with these settings, select OK.

In the next dialog, specify the interface type for your ISDN card and add ISPs to an existing interface. Interfaces may be either the SyncPPP or the RawIP type, but most ISPs operate in the SyncPPP mode, which is described below.

Figure 20.6. ISDN Interface Configuration

ISDN Interface Configuration

The number to enter for My Phone Number depends on your particular setup:

ISDN Card Directly Connected to Phone Outlet

A standard ISDN line provides three phone numbers (called multiple subscriber numbers, or MSNs). If the subscriber asked for more, there may be up to 10. One of these MSNs must be entered here, but without your area code. If you enter the wrong number, your phone operator automatically falls back to the first MSN assigned to your ISDN line.

ISDN Card Connected to a Private Branch Exchange

Again, the configuration may vary depending on the equipment installed:

  1. Smaller private branch exchanges (PBX) built for home purposes mostly use the Euro-ISDN (EDSS1) protocol for internal calls. These exchanges have an internal S0 bus and use internal numbers for the equipment connected to them.

    Use one of the internal numbers as your MSN. You should be able to use at least one of the exchange's MSNs that have been enabled for direct outward dialing. If this does not work, try a single zero. For further information, consult the documentation delivered with your phone exchange.

  2. Larger phone exchanges designed for businesses normally use the 1TR6 protocol for internal calls. Their MSN is called EAZ and usually corresponds to the direct-dial number. For the configuration under Linux, it should be sufficient to enter the last digit of the EAZ. As a last resort, try each of the digits from 1 to 9.

For the connection to be terminated just before the next charge unit is due, enable ChargeHUP. However, remember that may not work with every ISP. You can also enable channel bundling (multilink PPP) by selecting the corresponding option. Finally, you can enable the firewall for your link by selecting External Firewall Interface and Restart Firewall. To enable the normal user without administrator permissions to activate or deactivate the interface, select the Enable Device Control for Non-root User via KInternet.

Details opens a dialog in which to implement more complex connection schemes which are not relevant for normal home users. Leave the Details dialog by selecting OK.

In the next dialog, configure IP address settings. If you have not been given a static IP by your provider, select Dynamic IP Address. Otherwise, use the fields provided to enter your host's local IP address and the remote IP address according to the specifications of your ISP. If the interface should be the default route to the Internet, select Default Route. Each host can only have one interface configured as the default route. Leave this dialog by selecting Next.

The following dialog allows you to set your country and select an ISP. The ISPs included in the list are call-by-call providers only. If your ISP is not in the list, select New. This opens the Provider Parameters dialog in which to enter all the details for your ISP. When entering the phone number, do not include any blanks or commas among the digits. Finally, enter your login and the password as provided by the ISP. When finished, select Next.

To use Dial on Demand on a stand-alone workstation, specify the name server (DNS server) as well. Most ISPs support dynamic DNS, which means the IP address of a name server is sent by the ISP each time you connect. For a single workstation, however, you still need to provide a placeholder address like 192.168.22.99. If your ISP does not support dynamic DNS, specify the name server IP addresses of the ISP. If desired, specify a time-out for the connection—the period of network inactivity (in seconds) after which the connection should be automatically terminated. Confirm your settings with Next. YaST displays a summary of the configured interfaces. To activate these settings, select OK.

20.4.4. Cable Modem

[Tip]IBM System z: Cable Modem

The configuration of this type of hardware is not supported on IBM System z platforms.

In some countries it is quite common to access the Internet through the TV cable network. The TV cable subscriber usually gets a modem that is connected to the TV cable outlet on one side and to a computer network card on the other (using a 10Base-TG twisted pair cable). The cable modem then provides a dedicated Internet connection with a fixed IP address.

Depending on the instructions provided by your ISP, when configuring the network card either select Dynamic Address or Statically Assigned IP Address. Most providers today use DHCP. A static IP address often comes as part of a special business account.

20.4.5. DSL

[Tip]IBM System z: DSL

The configuration of this type of hardware is not supported on IBM System z platforms.

To configure your DSL device, select the DSL module from the YaST Network Devices section. This YaST module consists of several dialogs in which to set the parameters of DSL links based on one of the following protocols:

  • PPP over Ethernet (PPPoE)

  • PPP over ATM (PPPoATM)

  • CAPI for ADSL (Fritz Cards)

  • Point-to-Point Tunneling Protocol (PPTP)—Austria

In the DSL Devices tab of the DSL Configuration Overview dialog, you will find a list of installed DSL devices. To change the configuration of a DSL device, select it in the list and click Edit. If you click Add, you can manually configure a new DSL device.

The configuration of a DSL connection based on PPPoE or PPTP requires that the corresponding network card be set up in the correct way. If you have not done so yet, first configure the card by selecting Configure Network Cards (see Section 20.4.1, “Configuring the Network Card with YaST”). In the case of a DSL link, addresses may be assigned automatically but not via DHCP, which is why you should not enable the option Dynamic Address. Instead, enter a static dummy address for the interface, such as 192.168.22.1. In Subnet Mask, enter 255.255.255.0. If you are configuring a stand-alone workstation, leave Default Gateway empty.

[Tip]

Values in IP Address and Subnet Mask are only placeholders. They are only needed to initialize the network card and do not represent the DSL link as such.

In the first DSL configuration dialog (see Figure 20.7, “DSL Configuration”), select the PPP Mode and the Ethernet Card to which the DSL modem is connected (in most cases, this is eth0). Then use Activate Device to specify whether the DSL link should be established during the boot process. Click Enable Device Control for Non-root User via KInternet to authorize the normal user without root permissions to activate or deactivate the interface with KInternet.

In the next dialog select your country and choose from a number of ISPs operating in it. The details of any subsequent dialogs of the DSL configuration depend on the options set so far, which is why they are only briefly mentioned in the following paragraphs. For details on the available options, read the detailed help available from the dialogs.

Figure 20.7. DSL Configuration

DSL Configuration

To use Dial on Demand on a stand-alone workstation, also specify the name server (DNS server). Most ISPs support dynamic DNS—the IP address of a name server is sent by the ISP each time you connect. For a single workstation, however, provide a placeholder address like 192.168.22.99. If your ISP does not support dynamic DNS, enter the name server IP address provided by your ISP.

Idle Time-Out (seconds) defines a period of network inactivity after which to terminate the connection automatically. A reasonable time-out value is between 60 and 300 seconds. If Dial on Demand is disabled, it may be useful to set the time-out to zero to prevent automatic hang-up.

The configuration of T-DSL is very similar to the DSL setup. Just select T-Online as your provider and YaST opens the T-DSL configuration dialog. In this dialog, provide some additional information required for T-DSL—the line ID, the T-Online number, the user code and your password. All of these should be included in the information you received after subscribing to T-DSL.

20.4.6. IBM System z: Configuring Network Devices

SUSE Linux Enterprise Server for IBM System z supports several different types of network interfaces. YaST can be used to configure all of them.

20.4.6.1. The qeth-hsi Device

To add a qeth-hsi (Hipersockets) interface to the installed system, start the Network Devices+Network Settings module in YaST. Select one of the devices marked Hipersocket to use as the READ device address and click Edit. Enter the device numbers for the read, write and control channels (example device number format: 0.0.0600). Then click next. In the Network Address Setup dialog, specify the IP address and netmask for the new interface and leave the network configuration by pressing Next and OK.

20.4.6.2. The qeth-ethernet Device

To add a qeth-ethernet (IBM OSA Express Ethernet Card) interface to the installed system, start the Network Devices+Network Settings module in YaST. Select one of the devices marked IBM OSA Express Ethernet Card to use as the READ device address and click Edit. Enter a device number for the read, write and control channels (example device number format: 0.0.0600). Enter the needed port name, port number (if applicable) and some additional options (see the Linux for IBM System z: Device Drivers, Features, and Commands manual for reference, http://www.ibm.com/developerworks/linux/linux390/documentation_novell_suse.html), your IP address, and an appropriate netmask. Leave the network configuration with Next and OK.

20.4.6.3. The ctc Device

To add a ctc (IBM parallel CTC Adapter) interface to the installed system, start the Network Devices+Network Settings module in YaST. Select one of the devices marked IBM Parallel CTC Adapter to use as your read channel and click Configure. Choose the Device Settings that fit your devices (usually this would be Compatibility Mode). Specify both your IP address and the IP address of the remote partner. If needed, adjust the MTU size with Advanced+Detailed Settings. Leave the network configuration with Next and OK.

[Warning]

The use of this interface is deprecated. This interface will not be supported in future versions of SUSE Linux Enterprise Server.

20.4.6.4. The lcs Device

To add an lcs (IBM OSA-2 Adapter) interface to the installed system, start the Network Devices+Network Settings module in YaST. Select one of the devices marked IBM OSA-2 Adapter and click Configure. Enter the needed port number, some additional options (see the Linux for IBM System z: Device Drivers, Features, and Commands manual for reference, http://www.ibm.com/developerworks/linux/linux390/documentation_novell_suse.html), your IP address and an appropriate netmask. Leave the network configuration with Next and OK.

20.4.6.5. The IUCV Device

To add an iucv (IUCV) interface to the installed system, start the Network Devices+Network Settings module in YaST. Select a device marked IUCV and click Edit. YaST prompts you for the name of your IUCV partner (Peer). Enter the name (this entry is case-sensitive) and select Next. Specify both the IP Address and the Remote IP Address of your partner. If needed, Set MTU size on General tab. Leave the network configuration with Next and OK.

[Warning]

The use of this interface is deprecated. This interface will not be supported in future versions of SUSE Linux Enterprise Server.

20.5. NetworkManager

NetworkManager is the ideal solution for laptops and other portable computers. With NetworkManager, you do not need to worry about configuring network interfaces and switching between networks when you are moving.

20.5.1. NetworkManager and ifup

However, NetworkManager is not a suitable solution for all cases, so you can still choose between the traditional method for managing network connections (ifup) and NetworkManager. If you want to manage your network connection with NetworkManager, enable NetworkManager in the YaST Network Settings module as described in Section 25.2, “Enabling NetworkManager” and configure your network connections with NetworkManager. For a list of use cases and a detailed description how to configure and use NetworkManager, refer to Chapter 25, Using NetworkManager.

Some differences between ifup and NetworkManager include:

root Privileges

If you use NetworkManager for network setup, you can easily switch, stop or start your network connection at any time from within your desktop environment using an applet. NetworkManager also makes it possible to change and configure wireless card connections without requiring root privileges. For this reason, NetworkManager is the ideal solution for a mobile workstation.

Traditional configuration with ifup also provides some ways to switch, stop or start the connection with or without user intervention, like user-managed devices. However, this always requires root privileges to change or configure a network device. This is often a problem for mobile computing, where it is not possible to preconfigure all the connection possibilities.

Types of Network Connections

Both traditional configuration and NetworkManager can handle network connections with a wireless network (with WEP, WPA-PSK, and WPA-Enterprise access) and wired networks using DHCP and static configuration. They also support connection through dial-up, DSL and VPN. With NetworkManager you can also connect a mobile broadband (3G) modem, which is not possible with the traditional configuration.

NetworkManager tries to keep your computer connected at all times using the best connection available. If the network cable is accidentally disconnected, it tries to reconnect. It can find the network with the best signal strength from the list of your wireless connections and automatically use it to connect. To get the same functionality with ifup, a great deal of configuration effort is required.

20.5.2. NetworkManager Functionality and Configuration Files

The individual network connection settings created with NetworkManager are stored in configuration profiles. The system connections configured with either NetworkManager or YaST are saved in /etc/networkmanager/system-connections/* or in /etc/sysconfig/network/ifcfg-*. Any user-defined connections are stored in GConf for GNOME or $HOME/.kde4/share/apps/networkmanagement/* for KDE.

In case no profile is configured, NetworkManager automatically creates one and names it Auto $INTERFACE-NAME. That is made in an attempt to work without any configuration for as many cases as (securely) possible. If the automatically created profiles do not suit your needs, use the network connection configuration dialogs provided by KDE or GNOME to modify them as desired. For more information, refer to Section 25.3, “Configuring Network Connections”.

20.5.3. Controlling and Locking Down NetworkManager Features

On centrally administered machines, certain NetworkManager features can be controlled or disabled with PolicyKit, for example if a user is allowed to modify administrator defined connections or if a user is allowed to define his own network configurations. To view or change the respective NetworkManager policies, start the graphical Authorizations tool for PolicyKit. In the tree on the left side, find them below the network-manager-settings entry. For an introduction to PolicyKit and details on how to use it, refer to Chapter 9, PolicyKit (↑Security Guide).

20.6. Configuring a Network Connection Manually

Manual configuration of the network software should always be the last alternative. Using YaST is recommended. However, this background information about the network configuration can also assist your work with YaST.

When the Kernel detects a network card and creates a corresponding network interface, it assigns the device a name depending on the order of device discovery, or order of the loading of the Kernel modules. The default Kernel device names are only predictable in very simple or tightly controlled hardware environments. Systems which allow adding or removing hardware during runtime or support automatic configuration of devices cannot expect stable network device names assigned by the Kernel across reboots.

However, all system configuration tools rely on persistent interface names. This problem is solved by udev. The udev persistent net generator (/lib/udev/rules.d/75-persistent-net-generator.rules) generates a rule matching the hardware (using its hardware address by default) and assigns a persistently unique interface for the hardware. The udev database of network interfaces is stored in the file /etc/udev/rules.d/70-persistent-net.rules. Every line in the file describes one network interface and specifies its persistent name. System administrators can change the assigned names by editing the NAME="" entries. The persistent rules can also be modified using YaST.

Table 20.5, “Manual Network Configuration Scripts” summarizes the most important scripts involved in the network configuration.

Table 20.5. Manual Network Configuration Scripts

Command

Function

ifup, ifdown, ifstatus

The if scripts start or stop network interfaces, or return the status of the specified interface. For more information, see the ifup manual page.

rcnetwork

The rcnetwork script can be used to start, stop or restart all network interfaces (or just a specified one). Use rcnetwork stop to stop, rcnetwork start to start and rcnetwork restart to restart network interfaces. If you want to stop, start or restart just one interface, use the command followed by the interface name, for example rcnetwork restart eth0. The rcnetwork status command displays the state of the interfaces, their IP addresses and whether a DHCP client is running. With rcnetwork stop-all-dhcp-clients and rcnetwork restart-all-dhcp-clients you can stop or restart DHCP clients running on network interfaces.


For more information about udev and persistent device names, see Chapter 13, Dynamic Kernel Device Management with udev.

20.6.1. Configuration Files

This section provides an overview of the network configuration files and explains their purpose and the format used.

20.6.1.1. /etc/sysconfig/network/ifcfg-*

These files contain the configurations for network interfaces. They include information such as the start mode and the IP address. Possible parameters are described in the manual page of ifup. Additionally, most variables from the dhcp file can be used in the ifcfg-* files if a general setting should be used for only one interface. However, most of the /etc/sysconfig/network/config variables are global and cannot be overridden in ifcfg-files. For example NETWORKMANAGER or NETCONFIG_* variables are global.

For ifcfg.template, see Section 20.6.1.2, “/etc/sysconfig/network/config and /etc/sysconfig/network/dhcp.

►zseries: IBM System z do not support USB. The names of the interface files and network aliases contain System z-specific elements like qeth.

20.6.1.2. /etc/sysconfig/network/config and /etc/sysconfig/network/dhcp

The file config contains general settings for the behavior of ifup, ifdown and ifstatus. dhcp contains settings for DHCP. The variables in both configuration files are commented. Some of the variables from /etc/sysconfig/network/config can also be used in ifcfg-* files, where they are given a higher priority. The /etc/sysconfig/network/ifcfg.template file lists variables that can be specified in a per interface scope. However, most of the /etc/sysconfig/network/config variables are global and cannot be overridden in ifcfg-files. For example, NETWORKMANAGER or NETCONFIG_* variables are global.

20.6.1.3. /etc/sysconfig/network/routes and /etc/sysconfig/network/ifroute-*

The static routing of TCP/IP packets is determined here. All the static routes required by the various system tasks can be entered in the /etc/sysconfig/network/routes file: routes to a host, routes to a host via a gateway and routes to a network. For each interface that needs individual routing, define an additional configuration file: /etc/sysconfig/network/ifroute-*. Replace * with the name of the interface. The entries in the routing configuration files look like this:

# Destination     Dummy/Gateway     Netmask            Device
#
127.0.0.0         0.0.0.0           255.255.255.0      lo
204.127.235.0     0.0.0.0           255.255.255.0      eth0
default           204.127.235.41    0.0.0.0            eth0
207.68.156.51     207.68.145.45     255.255.255.255    eth1
192.168.0.0       207.68.156.51     255.255.0.0        eth1

The route's destination is in the first column. This column may contain the IP address of a network or host or, in the case of reachable name servers, the fully qualified network or hostname.

The second column contains the default gateway or a gateway through which a host or network can be accessed. The third column contains the netmask for networks or hosts behind a gateway. For example, the mask is 255.255.255.255 for a host behind a gateway.

The fourth column is only relevant for networks connected to the local host such as loopback, Ethernet, ISDN, PPP and dummy device. The device name must be entered here.

An (optional) fifth column can be used to specify the type of a route. Columns that are not needed should contain a minus sign - to ensure that the parser correctly interprets the command. For details, refer to the routes(5) man page.

The unified format for IPv4 and IPv6 now looks as follows:

prefix/lengthgateway -            [interface]

And the so-called compatibility format looks accordingly:

prefixgatewaylength       [interface]

For IPv4 you still can use the old format with netmask:

ipv4-networkgatewayipv4-netmask [interface]

The following examples are equivalent:

2001:db8:abba:cafe::/64 2001:db8:abba:cafe::dead  -            eth0
208.77.188.0/24         208.77.188.166            -            eth0

2001:db8:abba:cafe::    2001:db8:abba:cafe::dead 64            eth0
208.77.188.0            208.77.188.166           24            eth0

208.77.188.0            208.77.188.166           255.255.255.0 eth0

20.6.1.4. /etc/resolv.conf

The domain to which the host belongs is specified in this file (keyword search). Also listed is the status of the name server address to access (keyword nameserver). Multiple domain names can be specified in the file. When resolving a name that is not fully qualified, an attempt is made to generate one by attaching the individual search entries. Multiple name servers can be specified in multiple lines, each beginning with nameserver. Comments are preceded by # signs. Example 20.5, “/etc/resolv.conf shows what /etc/resolv.conf could look like.

However, the /etc/resolv.conf should not be edited by hand. Instead, it is generated by the netconfig script. To define static DNS configuration without using YaST, edit the appropriate variables manually in the /etc/sysconfig/network/config file:

NETCONFIG_DNS_STATIC_SEARCHLIST

list of DNS domain names used for hostname lookup

NETCONFIG_DNS_STATIC_SERVERS

list of name server IP addresses to use for hostname lookup

NETCONFIG_DNS_FORWARDER

defines the name of the DNS forwarder that has to be configured

To disable DNS configuration using netconfig, set NETCONFIG_DNS_POLICY=''. For more information about netconfig, see man 8 netconfig.

Example 20.5. /etc/resolv.conf

# Our domain
search example.com
#
# We use dns.example.com (192.168.1.116) as nameserver
nameserver 192.168.1.116

20.6.1.5. /sbin/netconfig

netconfig is a modular tool to manage additional network configuration settings. It merges statically defined settings with settings provided by autoconfiguration mechanisms as DHCP or PPP according to a predefined policy. The required changes are applied to the system by calling the netconfig modules that are responsible for modifying a configuration file and restarting a service or a similar action.

netconfig recognizes three main actions. The netconfig modify and netconfig remove commands are used by daemons such as DHCP or PPP to provide or remove settings to netconfig. Only the netconfig update command is available for the user:

modify

The netconfig modify command modifies the current interface and service specific dynamic settings and updates the network configuration. Netconfig reads settings from standard input or from a file specified with the --lease-file filename option and internally stores them until a system reboot (or the next modify or remove action). Already existing settings for the same interface and service combination are overwritten. The interface is specified by the -i interface_name parameter. The service is specified by the -s service_name parameter.

remove

The netconfig remove command removes the dynamic settings provided by a modificatory action for the specified interface and service combination and updates the network configuration. The interface is specified by the -i interface_name parameter. The service is specified by the -s service_name parameter.

update

The netconfig update command updates the network configuration using current settings. This is useful when the policy or the static configuration has changed. Use the -m module_type parameter, if you want to update a specified service only (dns, nis, or ntp).

The netconfig policy and the static configuration settings are defined either manually or using YaST in the /etc/sysconfig/network/config file. The dynamic configuration settings provided by autoconfiguration tools as DHCP or PPP are delivered directly by these tools with the netconfig modify and netconfig remove actions. NetworkManager also uses netconfig modify and netconfig remove actions. When NetworkManager is enabled, netconfig (in policy mode auto) uses only NetworkManager settings, ignoring settings from any other interfaces configured using the traditional ifup method. If NetworkManager does not provide any setting, static settings are used as a fallback. A mixed usage of NetworkManager and the traditional ifup method is not supported.

For more information about netconfig, see man 8 netconfig.

20.6.1.6. /etc/hosts

In this file, shown in Example 20.6, “/etc/hosts, IP addresses are assigned to hostnames. If no name server is implemented, all hosts to which an IP connection will be set up must be listed here. For each host, enter a line consisting of the IP address, the fully qualified hostname, and the hostname into the file. The IP address must be at the beginning of the line and the entries separated by blanks and tabs. Comments are always preceded by the # sign.

Example 20.6. /etc/hosts

127.0.0.1 localhost
192.168.2.100 jupiter.example.com jupiter
192.168.2.101 venus.example.com venus

20.6.1.7. /etc/networks

Here, network names are converted to network addresses. The format is similar to that of the hosts file, except the network names precede the addresses. See Example 20.7, “/etc/networks.

Example 20.7. /etc/networks

loopback     127.0.0.0
localnet     192.168.0.0

20.6.1.8. /etc/host.conf

Name resolution—the translation of host and network names via the resolver library—is controlled by this file. This file is only used for programs linked to libc4 or libc5. For current glibc programs, refer to the settings in /etc/nsswitch.conf. A parameter must always stand alone in its own line. Comments are preceded by a # sign. Table 20.6, “Parameters for /etc/host.conf” shows the parameters available. A sample /etc/host.conf is shown in Example 20.8, “/etc/host.conf.

Table 20.6. Parameters for /etc/host.conf

order hosts, bind

Specifies in which order the services are accessed for the name resolution. Available arguments are (separated by blank spaces or commas):

hosts: searches the /etc/hosts file

bind: accesses a name server

nis: uses NIS

multi on/off

Defines if a host entered in /etc/hosts can have multiple IP addresses.

nospoof on spoofalert on/off

These parameters influence the name server spoofing but do not exert any influence on the network configuration.

trim domainname

The specified domain name is separated from the hostname after hostname resolution (as long as the hostname includes the domain name). This option is useful only if names from the local domain are in the /etc/hosts file, but should still be recognized with the attached domain names.


Example 20.8. /etc/host.conf

# We have named running
order hosts bind
# Allow multiple address
multi on

20.6.1.9. /etc/nsswitch.conf

The introduction of the GNU C Library 2.0 was accompanied by the introduction of the Name Service Switch (NSS). Refer to the nsswitch.conf(5) man page and The GNU C Library Reference Manual for details.

The order for queries is defined in the file /etc/nsswitch.conf. A sample nsswitch.conf is shown in Example 20.9, “/etc/nsswitch.conf. Comments are preceded by # signs. In this example, the entry under the hosts database means that a request is sent to /etc/hosts (files) via DNS (see Chapter 23, The Domain Name System).

Example 20.9. /etc/nsswitch.conf

passwd:     compat
group:      compat

hosts:      files dns
networks:   files dns

services:   db files
protocols:  db files
rpc:        files
ethers:     files
netmasks:   files
netgroup:   files nis
publickey:  files

bootparams: files
automount:  files nis
aliases:    files nis
shadow:     compat

The databases available over NSS are listed in Table 20.7, “Databases Available via /etc/nsswitch.conf”. The configuration options for NSS databases are listed in Table 20.8, “Configuration Options for NSS Databases.

Table 20.7. Databases Available via /etc/nsswitch.conf

aliases

Mail aliases implemented by sendmail; see man 5 aliases.

ethers

Ethernet addresses.

netmasks

List of network and their subnet masks. Only needed, if you use subnetting.

group

For user groups used by getgrent. See also the man page for group.

hosts

For hostnames and IP addresses, used by gethostbyname and similar functions.

netgroup

Valid host and user lists in the network for the purpose of controlling access permissions; see the netgroup(5) man page.

networks

Network names and addresses, used by getnetent.

publickey

Public and secret keys for Secure_RPC used by NFS and NIS+..

passwd

User passwords, used by getpwent; see the passwd(5) man page.

protocols

Network protocols, used by getprotoent; see the protocols(5) man page.

rpc

Remote procedure call names and addresses, used by getrpcbyname and similar functions.

services

Network services, used by getservent.

shadow

Shadow passwords of users, used by getspnam; see the shadow(5) man page.


Table 20.8. Configuration Options for NSS Databases

files

directly access files, for example, /etc/aliases

db

access via a database

nis, nisplus

NIS, see also Chapter 3, Using NIS (↑Security Guide)

dns

can only be used as an extension for hosts and networks

compat

can only be used as an extension for passwd, shadow and group


20.6.1.10. /etc/nscd.conf

This file is used to configure nscd (name service cache daemon). See the nscd(8) and nscd.conf(5) man pages. By default, the system entries of passwd and groups are cached by nscd. This is important for the performance of directory services, like NIS and LDAP, because otherwise the network connection needs to be used for every access to names or groups. hosts is not cached by default, because the mechanism in nscd to cache hosts makes the local system unable to trust forward and reverse lookup checks. Instead of asking nscd to cache names, set up a caching DNS server.

If the caching for passwd is activated, it usually takes about fifteen seconds until a newly added local user is recognized. Reduce this waiting time by restarting nscd with the command rcnscd restart.

20.6.1.11. /etc/HOSTNAME

This contains the fully qualified hostname with the domain name attached. This file is read by several scripts while the machine is booting. It must contain only one line (in which the hostname is set).

20.6.2. Testing the Configuration

Before you write your configuration to the configuration files, you can test it. To set up a test configuration, use the ip command. To test the connection, use the ping command. Older configuration tools, ifconfig and route, are also available.

The commands ip, ifconfig and route change the network configuration directly without saving it in the configuration file. Unless you enter your configuration in the correct configuration files, the changed network configuration is lost on reboot.

20.6.2.1. Configuring a Network Interface with ip

ip is a tool to show and configure network devices, routing, policy routing, and tunnels.

ip is a very complex tool. Its common syntax is ip options object command. You can work with the following objects:

link

This object represents a network device.

address

This object represents the IP address of device.

neighbor

This object represents a ARP or NDISC cache entry.

route

This object represents the routing table entry.

rule

This object represents a rule in the routing policy database.

maddress

This object represents a multicast address.

mroute

This object represents a multicast routing cache entry.

tunnel

This object represents a tunnel over IP.

If no command is given, the default command is used (usually list).

Change the state of a device with the command ip link set device_name command. For example, to deactivate device eth0, enter ip link set eth0 down. To activate it again, use ip link set eth0 up.

After activating a device, you can configure it. To set the IP address, use ip addr add ip_address + dev device_name. For example, to set the address of the interface eth0 to 192.168.12.154/30 with standard broadcast (option brd), enter ip addr add 192.168.12.154/30 brd + dev eth0.

To have a working connection, you must also configure the default gateway. To set a gateway for your system, enter ip route add gateway_ip_address. To translate one IP address to another, use nat: ip route add nat ip_address via other_ip_address.

To display all devices, use ip link ls. To display the running interfaces only, use ip link ls up. To print interface statistics for a device, enter ip -s link ls device_name. To view addresses of your devices, enter ip addr. In the output of the ip addr, also find information about MAC addresses of your devices. To show all routes, use ip route show.

For more information about using ip, enter ip help or see the ip(8) man page. The help option is also available for all ip subcommands. If, for example, you need help for ip addr, enter ip addr help. Find the ip manual in /usr/share/doc/packages/iproute2/ip-cref.pdf.

20.6.2.2. Testing a Connection with ping

The ping command is the standard tool for testing whether a TCP/IP connection works. It uses the ICMP protocol to send a small data packet, ECHO_REQUEST datagram, to the destination host, requesting an immediate reply. If this works, ping displays a message to that effect, which indicates that the network link is basically functioning.

ping does more than only test the function of the connection between two computers: it also provides some basic information about the quality of the connection. In Example 20.10, “Output of the Command ping”, you can see an example of the ping output. The second-to-last line contains information about the number of transmitted packets, packet loss, and total time of ping running.

As the destination, you can use a hostname or IP address, for example, ping example.com or ping 192.168.3.100. The program sends packets until you press Ctrl+C.

If you only need to check the functionality of the connection, you can limit the number of the packets with the -c option. For example to limit ping to three packets, enter ping -c 3 example.com.

Example 20.10. Output of the Command ping

ping -c 3 example.com
PING example.com (192.168.3.100) 56(84) bytes of data.
64 bytes from example.com (192.168.3.100): icmp_seq=1 ttl=49 time=188 ms
64 bytes from example.com (192.168.3.100): icmp_seq=2 ttl=49 time=184 ms
64 bytes from example.com (192.168.3.100): icmp_seq=3 ttl=49 time=183 ms
--- example.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2007ms
rtt min/avg/max/mdev = 183.417/185.447/188.259/2.052 ms

The default interval between two packets is one second. To change the interval, ping provides the option -i. For example, to increase the ping interval to ten seconds, enter ping -i 10 example.com.

In a system with multiple network devices, it is sometimes useful to send the ping through a specific interface address. To do so, use the -I option with the name of the selected device, for example, ping -I wlan1 example.com.

For more options and information about using ping, enter ping -h or see the ping (8) man page.

[Tip]Pinging IPv6 Addresses

For IPv6 addresses use the ping6 command. Note, to ping link-local addresses, you must specify the interface with -I. The following command works, if the address is reachable via eth1:

ping6 -I eth1 fe80::117:21ff:feda:a425

20.6.2.3. Configuring the Network with ifconfig

ifconfig is a network configuration tool.

[Note]ifconfig and ip

The ifconfig tool is obsolete. Use ip instead. In contrast to ip, you can use ifconfig only for interface configuration. It limits interface names to 9 characters.

Without arguments, ifconfig displays the status of the currently active interfaces. As you can see in Example 20.11, “Output of the ifconfig Command”, ifconfig has very well-arranged and detailed output. The output also contains information about the MAC address of your device (the value of HWaddr) in the first line.

Example 20.11. Output of the ifconfig Command

eth0      Link encap:Ethernet  HWaddr 00:08:74:98:ED:51
          inet6 addr: fe80::208:74ff:fe98:ed51/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:634735 errors:0 dropped:0 overruns:4 frame:0
          TX packets:154779 errors:0 dropped:0 overruns:0 carrier:1
          collisions:0 txqueuelen:1000
          RX bytes:162531992 (155.0 Mb)  TX bytes:49575995 (47.2 Mb)
          Interrupt:11 Base address:0xec80

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:8559 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8559 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:533234 (520.7 Kb)  TX bytes:533234 (520.7 Kb)    

wlan1     Link encap:Ethernet  HWaddr 00:0E:2E:52:3B:1D
          inet addr:192.168.2.4  Bcast:192.168.2.255  Mask:255.255.255.0
          inet6 addr: fe80::20e:2eff:fe52:3b1d/64 Scope:Link
          UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:50828 errors:0 dropped:0 overruns:0 frame:0
          TX packets:43770 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:45978185 (43.8 Mb)  TX bytes:7526693 (7.1 MB)

For more options and information about using ifconfig, enter ifconfig -h or see the ifconfig (8) man page.

20.6.2.4. Configuring Routing with route

route is a program for manipulating the IP routing table. You can use it to view your routing configuration and to add or remove routes.

[Note]route and ip

The program route is obsolete. Use ip instead.

route is especially useful if you need quick and comprehensible information about your routing configuration to determine problems with routing. To view your current routing configuration, enter route -n as root.

Example 20.12. Output of the route -n Command

route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.20.0.0       *               255.255.248.0   U         0 0          0 eth0
link-local      *               255.255.0.0     U         0 0          0 eth0
loopback        *               255.0.0.0       U         0 0          0 lo
default         styx.exam.com   0.0.0.0         UG        0 0          0 eth0

For more options and information about using route, enter route -h or see the route (8) man page.

20.6.3. Start-Up Scripts

Apart from the configuration files described above, there are also various scripts that load the network programs while the machine is booting. These are started as soon as the system is switched to one of the multiuser runlevels. Some of these scripts are described in Table 20.9, “Some Start-Up Scripts for Network Programs”.

Table 20.9. Some Start-Up Scripts for Network Programs

/etc/init.d/network

This script handles the configuration of the network interfaces. If the network service was not started, no network interfaces are implemented.

/etc/init.d/xinetd

Starts xinetd. xinetd can be used to make server services available on the system. For example, it can start vsftpd whenever an FTP connection is initiated.

/etc/init.d/rpcbind

Starts the rpcbind utility that converts RPC program numbers to universal addresses. It is needed for RPC services, such as an NFS server.

/etc/init.d/nfsserver

Starts the NFS server.

/etc/init.d/postfix

Controls the postfix process.

/etc/init.d/ypserv

Starts the NIS server.

/etc/init.d/ypbind

Starts the NIS client.


20.7. smpppd as Dial-up Assistant

Some home users do not have a dedicated line connecting them to the Internet. Instead, they use dial-up connections. Depending on the dial-up method (ISDN or DSL), the connection is controlled by ipppd or pppd. Basically, all that needs to be done to go online is to start these programs correctly.

If you have a flat-rate connection that does not generate any additional costs for the dial-up connection, simply start the respective daemon. Control the dial-up connection with a desktop applet or a command-line interface. If the Internet gateway is not the host you are using, you might want to control the dial-up connection by way of a network host.

This is where smpppd (SUSE Meta PPP Daemon) is involved. It provides a uniform interface for auxiliary programs and acts in two directions. First, it programs the required pppd or ipppd and controls its dial-up properties. Second, it makes various providers available to the user programs and transmits information about the current status of the connection. As smpppd can also be controlled by way of the network, it is suitable for controlling dial-up connections to the Internet from a workstation in a private subnetwork.

20.7.1. Configuring smpppd

The connections provided by smpppd are automatically configured by YaST. The actual dial-up programs KInternet and cinternet are also preconfigured. Manual settings are only required to configure additional features of smpppd such as remote control.

The configuration file of smpppd is /etc/smpppd.conf. By default, it does not enable remote control. The most important options of this configuration file are:

open-inet-socket = yes|no

To control smpppd via the network, set this option to yes. smpppd listens on port 3185. If this parameter is set to yes, the parameters bind-address, host-range and password must be set accordingly.

bind-address = ip address

If a host has several IP addresses, use this parameter to determine at which IP address smpppd should accept connections. The default is to listen at all addresses.

host-range = min ipmax ip

The parameter host-range defines a network range. Hosts whose IP addresses are within this range are granted access to smpppd. All hosts not within this range are denied access.

password = password

By assigning a password, limit the clients to authorized hosts. As this is a plain-text password, you should not overrate the security it provides. If no password is assigned, all clients are permitted to access smpppd.

slp-register = yes|no

With this parameter, the smpppd service can be announced in the network via SLP.

More information about smpppd is available in the smpppd(8) and smpppd.conf(5) man pages.

20.7.2. Configuring cinternet for Remote Use

cinternet can be used to control a local or remote smpppd. cinternet is the command-line counterpart to the graphical KInternet. To prepare these utilities for use with a remote smpppd, edit the configuration file /etc/smpppd-c.conf manually or using cinternet. This file only uses four options:

sites = list of sites

list of sites where the front-ends search for smpppd. The front-ends test the options in the order specified here. local orders the establishment of a connection to the local smpppd. gateway points to an smpppd on the gateway. config-file indicates that the connection should be established to the smpppd specified in the server and port options in /etc/smpppd-c.conf. slp orders the front-ends to connect to an smpppd found via SLP.

server = server

The host on which smpppd runs.

port = port

The port on which smpppd runs.

password = password

The password selected for smpppd.

If smpppd is active, try to access it. For example, with cinternet --verbose --interface-list. In case of difficulties at this point, refer to the smpppd-c.conf(5) and cinternet(8) man pages.