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IP Routing Primer by Robert Wright

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Gateway of Last Resort

In Figure 5-1, if RouterC did not have an explicit route to subnet 168.72.6.0 or the major network 168.72.0.0, it would need a gateway of last resort to send packets to this subnet.

Figure 5-1. The link between RouterA and RouterB has a different major network than all other networks.

In the following routing table from RouterC, you can see that RouterC has installed a gateway of last resort network 10.0.0.0 with a next hop of 168.71.9.1. You can also see that there is no route to 168.72.6.0 or 168.72.0.0.

RouterC#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP   D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area ...

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