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Chapter 8: AI2524 Protocol Configuration Steps
August 1997 Page 8-15
2524UM
Validate Source IP Addresses
To disable the default function that validates the source IP addresses
of incoming routing updates, type this command in router configura
tion mode:
no validate-update-source
Network Illustration
IGRP advertises three types of routes: interior, system, and exterior, as
shown in Figure 8-1. Interior routes are routes between subnets in the
network attached to a router interface. If the network attached to a
router is not subnetted, IGRP does not advertise interior routes.
Figure 8-1:Interior, System, and Exterior Routes
System routes are routes to networks within an autonomous system.
The Cisco IOS software derives system routes from directly connected
network interfaces and system route information provided by other
IGRP-speaking routers or access servers. System routes do not include
subnet information.
Exterior routes are routes to networks outside the autonomous system
that are considered when identifying a gateway of last resort. Th
Cisco IOS software chooses a gateway of last resort from the list of ex-
terior routes that IGRP provides. The software uses the gateway
(router) of last resort if it does not have a better route for a packet and
the destination is not a connected network. If the autonomous system
has more than one connection to an external network, different routers
can choose different exterior routers as the gateway of last resort.