CISCO IOS in a Nutshell

Snapshot DDR

In all the previous dial-up examples, we used static routes to define the routing tables for dial-up connections. On small networks, static routes are easily managed, but on larger networks they can quickly get out of hand. However, running a routing protocol in the presence of DDR is a problem, because normal routing protocols would keep DDR links up forever with their constant route updates. In some situations this might be acceptable, but it begs the question of why you’re using DDR in the first place.

Snapshot routing was designed to allow the use of routing protocols across DDR connections without keeping the line active constantly. As the name implies, snapshot routing means that the routing protocols are allowed to take a “snapshot” of the network’s state at specified intervals rather than sending and receiving constant updates. Therefore, dial-up links come up only at a configurable interval, which saves the headache of static route management and keeps the dial-up link’s usage to a minimum. Snapshot routing is compatible with RIP (IP and IPX), EIGRP, IGRP, RTMP (AppleTalk), and RTP (Vines), all of which are distance-vector protocols.

Configuring a link for snapshot routing requires one end to be a snapshot server and the other end to be a snapshot client. In this example, Office 1 has the local network 10.10.0.0 and serves as the snapshot server; Office 2 has the local network 10.11.0.0 and is the snapshot client. There are two dialer maps at each site: one ...