As noted in Figure 10-1, if a DR is elected, the election occurs after the routers have become neighbors, but before they send DD packets and reach the ExStart neighbor state. When an OSPF router reaches the 2-way state with the first neighbor on an interface, it has already received at least one Hello from that neighbor. If the Hello messages state a DR of 0.0.0.0—meaning none has been elected—the router waits before attempting to elect a DR. This typically occurs after ..
In both PIM-DM and PIM-SM, the Prune process on multiaccess networks operates differently from how it operates on point-to-point links. The reason for this difference is that when one router sends a Prune message on a multiaccess network, other routers might not want the link pruned by the upstream router. Figure 20-11 shows an example of this problem, along with the solution through a PIM Join message that is called a Prune Override. In this figure, R1 is forwarding the grou..
Unlike IGRP, EIGRP must establish neighbor relationships before updates are sent out. When an EIGRP process is configured on the router, the router begins to exchange EIGRP hello packets over the multicast address of 224.0.0.10. Neighbor relationships form between routers when they receive each other's hello packet. Over LAN broadcast media such as Ethernet, Token Ring, or FDDI, the hello packets are sent every 5 seconds. Over WAN multipoint interfaces with a bandwidth of T1 ..
Deterministic Root Bridge Placement
Based on the previous discussion, you should now agree that deterministically setting your Root Bridge is a must. In fact, you should always set more than one Root Bridge—one to act as the primary and another to act as a backup in the event the primary fails. If your bridged network is really large, you might want to even set a tertiary Root Bridge in case both the primary and the secondary fail. This section considers how to deterministically place Root Bridges in your ne..
Configuring Basic MPLS CE Routers
CE routers do not require any special software or configuration to work with an MPLS carrier. You just need to ensure that there are appropriate routing table entries to allow sites to communicate across the MPLS network. We will do this with static routes for now: Router-CE-A1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router-CE-A1(config)#interface FastEthernet0/0.1 Router-CE-A1(config-if)#encapsulation dot1Q 101 Router-CE-A1(..
