with the name zebra.conf.sav. The vtysh interface is a tool intended to simplify a complex configuration problem. In general, however, Linux routers do not have highly complex configurations; and the configurations, once set, do not change frequently. Additionally, a small configuration file must be created before vtysh can be used, and the final configuration files are often not much larger than the minimal ones that must be created by hand. For these reasons, you may find vtysh more useful as a tool for examining the router configuration than as a tool for modifying the configuration. Personally, I like vtysh; but if you prefer, you can build Zebra configuration files with your favorite text editor. It’s up to you. The following sections show a few reasonable Linux Zebra configurations. We configure a host to run RIPv2, an interior router to run RIPv2 and OSPF, and an exterior router to run OSPF and BGP. Running ripd Routing protocols are not limited to routers. It is possible to need a routing protocol on a Linux host. Suppose that you have a host on a network in which routing updates are distributed via RIPv2. This system is not a router, but because it is on a network segment with more than one router, you decide to configure it to listen to the RIPv2 updates that the routers are broadcasting. Listing 7.9 shows a possible ripd.conf file for this host. Listing 7.9: A Sample ripd.conf File ! Enable RIPV2, but don’t send updates ! Check that packets are authentic interface eth0 ip rip authentication string EZdozIt ! router rip passive-interface eth0 ! The RIPv2 configuration is very simple. The command router rip enables RIP. By default, Zebra uses RIPv2, which is capable of handling address masks and is compatible with RIP version 1. To force Zebra to use RIP version 1, a version 1 clause could be used with the router rip command, but using RIP version 1 is generally ill advised. The passive-interface clause is used because this host listens to routing updates, but does not send routing updates. This is equivalent to the -q option mentioned earlier for the routed command. passive-interface is used on hosts that listen for updated; routers that actively participate in the routing exchange use the network clause. The network clause uses the interface name to identify the interface over which routing updates are exchanged; for example, network eth0. Alternatively, it can use an IP address to identify the systems with which routing updates are exchanged. The IP address is defined with an address mask. For example, network 172.16.60.0/24 would exchange routing updates with any system on subnet 172.16.60.0. We will see the network clause in action when we configure an interior router. The interface statement is used to configure the network interface for RIP. In Listing 7.9, a RIPv2 authentication mode is set for the interface. In this example, a simple clear text password is used. Clear text passwords are used to help the router avoid accepting updates from misconfigured systems; it is not a security method. Stronger update authentication is available in the form of MD5 authentication. 213
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