Designated Routers on WANs and OSPF Network Types

Using a DR makes good sense on a LAN because it improves LSA flooding efficiency. Likewise, not using a DR on a point-to-point WAN link also makes sense, because with only two routers on the subnet, there is no inefficiency upon which to improve. However, on nonbroadcast multiaccess (NBMA) networks,...

Classful Distance-Vector to Link-State Protocol

For the sake of this discussion, imagine you are migrating from IGRP, which is the classful distance-vector protocol, to a link-state protocol, OSPF. Remember that both OSPF and IS-IS require hierarchy. The network in Figure 12-2 shows that no hierarchy exists in the network in question, so you must...

Understanding the Detrimental Effects of LDP Restart

At this point, the discussion turns to the issues that arise when the LDP control-plane component of an LSR restarts. As described earlier, an LDP session is established over TCP. When an LDP control-plane component on an LSR restarts, the restarting LSR (on which the control plane has restarted) lo...

Configuring OSPF

The first line in this configuration example defines the OSPF process: Router5(config)#router ospf 87 The OSPF process number (87) doesn't propagate outside of the router. So you can use a different value for every router in an AS. Note that this is different from EIGRP, where every router in ...

Controlling Neighborships Using EIGRP Authentication

EIGRP authentication causes routers to authenticate every EIGRP message. To do so, the routers should use the same preshared key (PSK), generating an MD5 digest for each EIGRP message based on that shared PSK. If a router configured for EIGRP authentication receives an EIGRP message, and the mess...

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