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Chapter 6
Troubleshooting TCP/IP Connectivity
D 172.16.30.4/30 [90/2195456] via 172.16.50.1,
00:00:18, Ethernet0/0
Router_C#
Router_B#sho 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
U - per-user static route, o - ODR
Gateway of last resort is 172.16.50.2 to network 0.0.0.0
172.16.0.0/16 is variably subnetted, 2 subnets, 2
masks
C 172.16.50.0/24 is directly connected, Ethernet0
C 172.16.30.4/30 is directly connected, Serial0
S* 0.0.0.0/0 [1/0] via 172.16.50.2
Router_B#
The difference between the two examples is that one is dynamically set by
using the ip default-network command, and the other is set by using a
static route. Both methods end with the same results. If Router B does not
have a route for a requested destination, it forwards the packet to the next
hop of 172.16.50.2.
An example was given previously that demonstrated the importance of
having a default gateway configured. The ping and traceroute commands
can be used to isolate default gateway problems. When the router uses a
dynamic method of selecting a default gateway, there is a greater possibility
that it may fail.
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