Filtering Sources Of Routing Information - Cisco IE-4000 Software Configuration Manual

Configuring IP Unicast Routing
Configuring Protocol-Independent Features
DETAILED STEPS
Command
1. configure terminal
2. router {bgp | rip | eigrp}
3. distribute-list {access-list-number |
access-list-name} out [interface-name |
routing process |
autonomous-system-number]
4. distribute-list {access-list-number |
access-list-name} in [type-number]
5. end
6. copy running-config startup-config
Use the no distribute-list in router configuration command to change or cancel a filter. To cancel suppression of network
advertisements in updates, use the no distribute-list out router configuration command.
EXAMPLE
In the following example, a prefix list and distribute list are defined to configure the BGP routing process to accept traffic
from only network 10.1.1.0/24, network 192.168.1.0, and network 10.108.0.0. An inbound route refresh is initiated to
activate the distribute-list.
Switch(config)# ip prefix-list RED permit 10.1.1.0/24
Switch(config)# ip prefix-1ist RED permit 10.108.0.0/16
Switch(config)# ip prefix-list RED permit 192.168.1.0/24
Switch(config)# router bgp 50000
Switch(config-router)# network 10.108.0.0
Switch(config-router)# distribute-list prefix RED in
Switch(config-router)# end
Switch# clear ip bgp in

Filtering Sources of Routing Information

Because some routing information might be more accurate than others, you can use filtering to prioritize information
coming from different sources. An administrative distance is a rating of the trustworthiness of a routing information
source, such as a router or group of routers. In a large network, some routing protocols can be more reliable than others.
By specifying administrative distance values, you enable the router to intelligently discriminate between sources of
routing information. The router always picks the route whose routing protocol has the lowest administrative distance.
Because each network has its own requirements, there are no general guidelines for assigning administrative distances.
BEFORE YOU BEGIN

Always set the administrative distance from the least to the most specific network.

Review the usage guidelines and additional examples for the distance command in the
Protocol-Independent Command
Purpose
Enter global configuration mode.
Enter router configuration mode.
Permit or deny routes from being advertised in
routing updates, depending upon the action listed in
the access list.
Suppress processing in routes listed in updates.
Return to privileged EXEC mode.
(Optional) Save your entries in the configuration file.
Reference.
921
Cisco IOS IP Routing: