Specify A Default Route Or Gateway Of Last Resort; Configure Ip Routing And Ip Protocols; Default Routes; Default Network - Cisco 4000 Series Hardware Installation Manual

Chapter 4 Configure Initial Router Settings on Cisco 4000 Series ISRs

Specify a Default Route or Gateway of Last Resort

This section describes how to specify a default route with IP routing enabled. For alternative methods of
specifying a default route, see the
Specifications Note.
The Cisco IOS-XE software uses the gateway (router) as a last resort if it does not have a better route
for a packet and if the destination is not a connected network. This section describes how to select a
network as a default route (a candidate route for computing the gateway of last resort). The way in which
routing protocols propagate the default route information varies for each protocol.

Configure IP Routing and IP Protocols

For comprehensive configuration information about IP routing and IP routing protocols, see the
Configuring IP Routing Protocol-Independent Feature
IP Routing
IP routing is automatically enabled in the Cisco ISO- XE software. When IP routing is configured, the
system will use a configured or learned route to forward packets, including a configured default route.
Note This task section does not apply when IP routing is disabled. To specify a default route when IP routing
is disabled, refer to the
Specifications Note at cisco.com.

Default Routes

A router might not be able to determine the routes to all other networks. To provide complete routing
capability, the common practice is to use some routers as smart routers and give the remaining routers
default routes to the smart router. (Smart routers have routing table information for the entire
internetwork.) These default routes can be passed along dynamically, or can be configured into the
individual routers.
Most dynamic interior routing protocols include a mechanism for causing a smart router to generate
dynamic default information that is then passed along to other routers.

Default Network

If a router has an interface that is directly connected to the specified default network, the dynamic
routing protocols running on the router generates or sources a default route. In the case of RIP, the router
will advertise the pseudonetwork 0.0.0.0. In the case of IGRP, the network itself is advertised and
flagged as an exterior route.
A router that is generating the default for a network may also need a default of its own. One way a router
can generate its own default is to specify a static route to the network 0.0.0.0 through the appropriate
device.
OL-32185-02
Configuring a Gateway of Last Resort Using IP Commands
Configuring a Gateway of Last Resort Using IP Commands
Hardware Installation Guide for Cisco 4000 Series Integrated Services Routers
Perform Initial Configuration on Cisco 4000 Series ISRs
at cisco.com.
Technical
Technical
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