Smallest Multi-Exit Discriminator

The purpose of the MED (or MULTI_EXIT_DISC) is to allow routers in one AS to tell routers in a neighboring AS how good a particular route is. In fact, because of how MED works, it is often called the BGP metric, even though it is not close to the top of the BGP decision process. Figure 13-11 shows a classic case for the use of MED, where a customer has two links connecting it to a single ISP. The ISP, aware of its best routes for 11.0.0.0/8 and 12.0.0.0/8, can set MED so that..

The OSPF network Command

Once OSPF is turned on, you must define the interfaces that are to participate in OSPF and the area that they reside in by using the following command:  Router(config-router)#network network-number wildcard-mask area area-number  Be careful with this command. It is the cause of many errors in configuration, normally due to a misapplication of the wildcard-mask parameter, either including too many or too few interfaces in a particular OSPF area.  Like RIP, th..

Updating the Routing Table in Active Mode with DUAL

Figure 3-6 shows feasible and advertised distance.  Figure 3-6. Feasible and Advertised Distance—Active Mode When no alternative route is found in the routing table, the following actions are taken (using the network in Figure 3-6 as an example). The topology table of Router A starts with a path (successor) of A to D to G to X. The feasible distance is 20, and the advertised distance from Router D is 15. When Router D dies, Router A must find an alternative path to ..

LANs: The Heart of the Internet

It is a little-recognized fact that LAN technologies, because of their low price/speed ratio, still form the "heart" of the Internet—the place in which large numbers of major providers meet to exchange traffic with other providers. The original MAE-East and Federal Exchange points were based on Ethernet until they were later upgraded to FDDI and then switched FDDI, using Gigaswitches from Digital.   ATM was used at one or two public exchange points. However, mor..

Simple Bridging

You can configure a router to bridge between two or more interfaces, as follows: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#bridge 1 protocol ieee Router1(config)#interface Ethernet0/0 Router1(config-if)#bridge-group 1 Router1(config-if)#exit Router1(config)#interface Ethernet0/1 Router1(config-if)#bridge-group 1 Router1(config-if)#exit Router1(config)#end With Integrated Routing and Bridging (IRB), you can a..