38-96
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
OL-12247-04
Chapter 38 Configuring IP Unicast Routing
Configuring Protocol-Independent Features
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 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 can cause 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 route for a network also might need a default route of its own. One
way a router can generate its own default router 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 default static route to a network:
Use the
no ip default-network
network number
global configuration command to remove the route.
When default information passes through a dynamic routing protocol, no further configuration is
required. The system periodically scans its routing table to choose the best default network as its default
route. IGRP networks might have 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, you can specify candidates for the
default route 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. Information redistribution from one routing protocol to another applies
to all supported IP-based routing protocols.
You can also conditionally control the redistribution of routes between routing domains by defining
enhanced packet filters or route maps between the two domains. The
match
and
set
route-map
configuration commands define the condition portion of a route map. The
match
command specifies that
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
ip default-network
network number
Specify a default network.
Step 3
end
Return to privileged EXEC mode.
Step 4
show ip route
Display the selected default route in the gateway of last resort output.
Step 5
copy running-config startup-config
(Optional) Save your entries in the configuration file.
