Specifying Default Routes And Networks; Using Route Maps To Redistribute Routing Information - Cisco Catalyst 3750-X Software Configuration Manual

Chapter 42 Configuring IP Unicast Routing
When an interface goes down, all static routes through that interface are removed from the IP routing
table. When the software can no longer find a valid next hop for the address specified as the forwarding
router's address in a static route, the static route is also removed from the IP routing table.

Specifying Default Routes and Networks

A router might not be able to learn the routes to all other networks. To provide complete routing
capability, you can 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 dynamically learned or can be configured in the individual routers. Most dynamic interior
routing protocols include a mechanism for causing a smart router to generate dynamic default
information that is then forwarded to other routers.
If a router has a directly connected interface to the specified default network, the dynamic routing
protocols running on that device generate a default route. In RIP, it advertises the pseudonetwork 0.0.0.0.
A router that is generating the default for a network also might 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.
Beginning in privileged EXEC mode, follow these steps to define a static route to a network as the static
default route:
Command
Step 1
configure terminal
Step 2 ip default-network network number
Step 3
end
Step 4
show ip route
Step 5
copy running-config startup-config
Use the no ip default-network network number global configuration command to remove the route.
When default information is passed 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 IGRP networks, there might be several candidate networks for the system default. Cisco
routers use administrative distance and metric information to set the default route or the gateway of last
resort.
If dynamic default information is not being passed to the system, candidates for the default route are
specified with the ip default-network global configuration command. If this network appears in the
routing table from any source, it is flagged as a possible choice for the default route. If the router has no
interface on the default network, but does have a path to it, the network is considered as a possible
candidate, and the gateway to the best default path becomes the gateway of last resort.

Using Route Maps to Redistribute Routing Information

The switch can run multiple routing protocols simultaneously, and it can redistribute information from
one routing protocol to another. Redistributing information from one routing protocol to another applies
to all supported IP-based routing protocols.
OL-21521-01
Purpose
Enter global configuration mode.
Specify a default network.
Return to privileged EXEC mode.
Display the selected default route in the gateway of last resort
display.
(Optional) Save your entries in the configuration file.
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
Configuring Protocol-Independent Features
42-93