Tue 17 Oct 2006
(routed assumes it’s as if the computer has more than one network interface), the routing daemon broadcasts its own updates. If the computer has only one network interface, routed considers it a host, and the routing daemon does not broadcast routing updates. Command-line options can be used to change this default behavior, regardless of the number of network interfaces installed in the computer. Use s to force the daemon to broadcast RIP updates; specify q to stop it from broadcasting update packets. The q argument is more useful than the s argument. Sometimes, you don’t want a computer with multiple network interfaces broadcasting routes. However, it is unusual to configure a host with only one network interface to broadcast RIP updates. routed does not require configuration, but it is possible to use the /etc/gateways file to pass supplemental routing information to the routing daemon. The /etc/gateways File routed broadcasts a RIP request immediately on startup, and uses the information in the RIP updates it receives to build a table. The entire reason for running a routing protocol is to use the information from that protocol to build the routing table. On the surface, adding static routes to a dynamic table doesn’t seem to make much sense, and generally there is no reason to do so. But it is possible that there are routers on your network that can’t or won’t provide RIP updates and that must be added to the table manually. The /etc/gateways file provides that capability, in case you need it. routed reads the /etc/gateways file during startup, and adds the routes defined there to the routing table. The sample entries from a gateways file are enough to illustrate its purpose because all entries in the file have the same basic format. Listing 7.4 shows two sample entries. Listing 7.4: A sample /etc/gateways file $ cat /etc/gateways net 0.0.0.0 gateway 172.16.55.254 metric 1 active net 172.16.50.0 gateway 172.16.55.36 metric 1 passive All entries start with the keywords net or host to indicate whether it is a host-specific route or a network route. The keyword is followed by the destination address. (The destination 0.0.0.0 is a special address that stands for the default route.) The destination address is followed by the keyword gateway and the IP address of the external gateway used to reach the destination. Next come the keyword metric and the cost assigned to this route. Normally, external gateways are given a cost of 1, but this is arbitrary, so you can assign a higher value if you want. Assigning a higher metric, however, makes sense only if you have two routes to the same destination, and if you want to prefer one of those routes over the other. All entries end with the keywords active or passive. An active router is expected to participate in the exchange of routing updates. If it fails to respond to routing requests and does not periodically broadcast RIP updates, it is removed from the routing table. This is the normal behavior expected of any RIP router. A passive router does not participate in the exchange of RIP updates. Perhaps the system runs a different routing protocol. Regardless of the reason, it is not required to participate, and is installed in the routing table as a permanent static route. 205
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