5.5 Static and Default Routing
5.5.10 Enabling snapshot routing
Snapshot routing is enabled through interface configuration commands . The central router is configured for snapshot routing by applying the snapshot server interface configuration command to its ISDN interfaces. The snapshot server command specifies the length of the active period and whether the router is allowed to dial remote sites to exchange routing updates in the absence of regular traffic.

The remote routers are configured for snapshot routing by applying the snapshot client command to each ISDN interface. The snapshot client interface configuration command specifies the following variables:

  • The length of the active period (which must match the length specified on the central router)
  • The length of the quiet period
  • Whether the router can dial the central router to exchange routing updates in the absence of regular traffic
  • Whether connections that are established to exchange user data can be used to exchange routing updates

Examine the configuration of the Central Router. The snapshot server interface configuration command enables snapshot routing. The "5" sets the length of the active period to five minutes.

Examine the configuration of the Home Router. The dialer map snapshot interface configuration command establishes a map (whose sequence number is 1) that the router uses to connect to the central site router for the exchange of routing updates. The name keyword specifies the name of the remote router that is associated with the dial string. Because the ppp authentication interface configuration command enables CHAP authentication, when this router dials the central router, it receives the host name of the central router and compares it with the name specified by the name keyword.

The snapshot client interface configuration command sets the length of the active period to five minutes (a value that must match the value set in the snapshot server's configuration) and sets the length of the quiet period to 43,200 seconds (12 hours). The suppress-statechange-updates keyword prevents the routers from exchanging updates during connections that are established to transfer user data. The dialer keyword allows the client router to dial up the server router in the absence of regular traffic and is required when you use the suppress-statechange-update keyword.

When the backbone routing protocol is not supported by snapshot routing (for example, OSPF or EIGRP), standard routing redistribution techniques can be used to ensure that routing updates are propagated between routing protocols, as required. Care should be taken to ensure redistribution of subnets if needed and to avoid routing loops.
Lab Activity    
  The Phoenix and Denver offices want to exchange routing updates without incurring large telecommunication bills. Your solution is to configure snapshot routing between the two routers.