System Administration Guide: IP Services

Configuring Routers

TCP/IP's first requirement for a router is that the machine must have at least two network interfaces installed. If one of the network interfaces is not disabled, the router automatically “talks” to the RDISC and RIP protocols. These protocols monitor routers on the network and advertise the router to the hosts on the network.

After the router is physically installed on the network, configure the router to operate in local files mode, as described in How to Configure a Host for Local Files Mode. This configuration ensures that routers boot if the network configuration server is down. Remember that, unlike a host, a router has a minimum of two interfaces to configure.

Configuring Routers Task Map

Table 4–4 Configuring Routers Task Map

Task 

Description 

For Instructions, Go To ... 

Configure a machine as a router 

Involves creating hostname and hosts file and adding addresses

How to Configure a Machine as a Router

Select static routing on a host that is a network client 

Involves adding an entry into the defaultrouter file

How to Select Static Routing on a Host That Is a Network Client

Select dynamic routing on a host that is a network client 

Involves editing entries in the defaultrouter file

How to Select Dynamic Routing on a Host That Is a Network Client

Force a machine to be a router 

Involves creating a gateways file

How to Force a Machine to Be a Router

Configuring Both Router Network Interfaces

Because a router provides the interface between two or more networks, you must assign a unique name and IP address to each of the router's network interface cards. Thus, each router has a host name and an IP address that are associated with its primary network interface, plus a minimum of one more unique name and an IP address for each additional network interface.

How to Configure a Machine as a Router

  1. Become superuser on the machine to be configured as a router.

  2. Create an /etc/hostname.interface file for each network interface that is installed.

    For example, create hostname.ie0 and hostname.ie1. See /etc/hostname.interface File for more information. If you are using IPv6, see IPv6 Network Interface Configuration File.

  3. In each file, type the host name you have selected for that interface.

    For example, you could type the name timbuktu in the file hostname.ie0, then type the name timbuktu-201 in the file hostname.ie1. Both interfaces would be located on the same machine.

  4. Type the host name and IP address of each interface into /etc/inet/hosts.

    For example:


    192.9.200.20     timbuktu       #interface for network 192.9.200
    192.9.201.20     timbuktu-201   #interface for network 192.9.201
    192.9.200.9      gobi
    192.9.200.10     mojave
    192.9.200.110    saltlake
    192.9.200.12     chilean

    The interfaces timbuktu and timbuktu-201 are on the same machine. Notice that the network address for timbuktu-201 is different from that of timbuktu. The difference exists because the medium for network 192.9.201 is connected to the timbuktu-201 network interface while the media for network 192.9.200 is connected to the timbuktu interface. If you are using IPv6, see /etc/inet/ipnodes File.

  5. If the router is connected to any subnetted network, edit /etc/inet/netmasks and type the local network number (129.9.0.0, for example) and associated netmask number (255.255.255.0, for example).

The startup script determines whether to start up a routing protocol (RIP or RDISC) on the machine or use static routing.

How to Select Static Routing on a Host That Is a Network Client

  1. Become superuser on the host.

  2. Add an entry for a router on the network into the /etc/defaultrouter file.

See /etc/defaultrouter File. A single static default route is then installed in the routing table. Under this condition, the host does not run any dynamic routing protocol (such as RIP and RDISC).

How to Select Dynamic Routing on a Host That Is a Network Client

  1. Become superuser on the host.

  2. Ensure that the /etc/defaultrouter file is empty.

    If this file is empty, a network client is forced to select a dynamic routing protocol.

The type of dynamic routing used is selected by using the following criteria:

How to Force a Machine to Be a Router

You can force a machine that has only one /etc/hostname.interface file (by default a host) to be a router.

  1. Become superuser on the machine.

  2. Create a file that is named /etc/gateways and leave this file empty.

This procedure is important if you decide to configure PPP links, as explained in System Administration Guide: Resource Management and Network Services.