Flooding LSA Headers to Neighbors

Once two routers hear Hellos, and the parameter check passes, they do not immediately send packets holding the LSAs. Instead, each router creates and sends Database Description (DD, or sometimes called DBD) packets, which contain the headers of each LSA. The headers include enough information to uniquely identify each LSA. Essentially, the routers exchange a list of all the LSAs they each know about; the next step in the process is letting a router request a new copy of any o..

RIP Convergence When Routing Updates Cease

When a router ceases to receive routing updates, RIP must wait for some timers to expire before it decides that routes previously learned from the now-silent router can be considered to be failed routes. To deal with such cases, RIP uses its Invalid, Flush, and Holddown timers to prevent loops. Coincidentally, RIP’s convergence time increases to several minutes as a result. Example 8-3 details just such a case, where R1 simply ceases to hear RIP updates from R3. (To create..

Steady-State Operation and the State Refresh Message

As mentioned briefly earlier in the chapter, with PIM-DM, an interface stays pruned only for 3 minutes by default. Prune messages list a particular source and group (in other words, a particular (S,G) SPT). Whenever a router receives a Prune message, it finds the matching (S,G) SPT entry and marks the interface on which the Prune message was received as “pruned.” However, it also sets a Prune timer, default 3 minutes, so that after 3 minutes, the interface is placed into ..

GP/MPLS Graceful Restart Operation

This section describes the operation of the BGP with an MPLS graceful restart mechanism using the network shown in Figure 7-11. The following discussion assumes that LSR1 and LSR2 are capable of both BGP with MPLS graceful restart and NSF. The following sequence of steps does not necessarily indicate the processing steps of a specific implementation. This description is intended to provide a functional view. •    During BGP session establishment, LSR1 and LS..

Monitoring and Troubleshooting CBWFQ for Frame Relay

The show policy-map privileged EXEC command can be used to display the configurations of all classes comprising the specified service policy map or all classes for all existing policy maps. A sample output of the show policy-map command is shown in Example 18-4. Example 18-4. Output of show policy-map Command at R1 R1#show policy-map   Policy Map CBWFQ     Class premium       Weighted Fair Queueing      &n..