Cisco 4331 ISR - Gateway of Last Resort

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Hardware Installation Guide for Cisco 4000 Series Integrated Services Routers
OL-32185-02
Chapter 4 Configure Initial Router Settings on Cisco 4000 Series ISRs
Perform Initial Configuration on Cisco 4000 Series ISRs
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-XE
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 for 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 based on administrative distance and
metric, the best one is chosen. The gateway to the best default path becomes the gateway of last resort.
SUMMARY STEPS
1. enable
2. configure terminal
3. ip route dest-prefix mask next-hop-ip-address [admin-distance] [permanent]
4. ip default-network network-number
or
ip route dest-prefix mask next-hop-ip-address
5. end
6. show ip route
DETAILED STEPS
Command or Action Purpose
Step 1
enable
Example:
Router> enable
Enables privileged EXEC mode. Enter your password if
prompted.
Step 2
configure terminal
Example:
Router# configure terminal
Enters global configuration mode.
Step 3
ip routing
Example:
Router(config)# ip routing
Enables IP routing.