Gateway Of Last Resort - Cisco 2900 series Installation Manual

Performing the Initial Configuration on the Router

Gateway of Last Resort

When default information is being passed along through a dynamic routing protocol, no further
configuration is required. The system periodically scans its routing table to choose the optimal default
network as its default route. In the case of RIP, there is only one choice, network 0.0.0.0. In the case of
IGRP, there might be several networks that can be candidates for the system default. The Cisco IOS
software uses both administrative distance and metric information to determine the default route
(gateway of last resort). The selected default route appears in the gateway of last resort display of the
show ip route EXEC command.
If dynamic default information is not being passed to the software, candidates for the default route are
specified with the ip default-network global configuration command. In this usage, the ip
default-network command takes an unconnected network as an argument. If this network appears in the
routing table from any source (dynamic or static), it is flagged as a candidate default route and is a
possible choice as the default route.
If the router has no interface on the default network, but does have a route to it, it considers this network
as a candidate default path. The route candidates are examined and the best one is chosen, based on
administrative distance and metric. The gateway to the best default path becomes the gateway of last
resort.
SUMMARY STEPS
1.
2.
3.
4.
5.
6.
7.
DETAILED STEPS
Command or Action
Step 1
enable
Example:
Router> enable
Step 2
configure terminal
Example:
Router# configure terminal
Step 3
ip routing
Example:
Router(config)# ip routing
Cisco 2900 and 3900 Series Hardware Installation
4-16
enable
configure terminal
ip routing
ip route dest-prefix mask next-hop-ip-address [admin-distance] [permanent]
ip default-network network-number
or
ip route dest-prefix mask next-hop-ip-address
end
show ip route
Purpose
Enables privileged EXEC mode.
Enter your password if prompted.
•
Enters global configuration mode.
Enables IP routing.
Chapter 4 Configuring the Router
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