January 2002
Beginner
238 pages
6h 20m
English
Content preview from IP Routing
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The Routing Table
At Grand Central Terminal, a big wall lists all the destinations and their corresponding track numbers (see Figure 1-4). Passengers find their destination on this wall and then proceed to the indicated platforms. Similarly, a routing table must contain at least two pieces of information: the destination network and the next hop toward that destination. This reflects a fundamental paradigm of IP routing: hop-by-hop routing. In other words, a router does not know the full path to a destination, but only the next hop to reach the destination.
Figure 1-4. Destinations and track numbers at Grand Central Terminal
Routes are installed in the routing table as they are learned through the mechanisms we have been discussing: directly connected networks, static routes, and dynamic routing protocols. A typical routing table in a Cisco router looks like this:
Router>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
2 177.130.0.0/30 is subnetted, 2 subnets C 177.130.17.152 is directly connected, Serial1 C 177.130.17.148 is directly connected, ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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