Filtering Sources Of Routing Information - Cisco Catalyst 3550 series Software Configuration Manual

Chapter 31 Configuring IP Unicast Routing
Command
Step 5 end
Step 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.

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.
the default administrative distances for various routing information sources.
Because each network has its own requirements, there are no general guidelines for assigning
administrative distances.
Beginning in privileged EXEC mode, follow these steps to filter sources of routing information:
Command
Step 1
configure terminal
Step 2 router {bgp |rip | ospf | igrp | eigrp}
Step 3 distance weight {ip-address {ip-address mask}}
[ip access list]
Step 4 end
Step 5
show ip protocols
Step 6
copy running-config startup-config
To remove a distance definition, use the no distance router configuration command.
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Configuring Protocol-Independent Features
Purpose
Return to privileged EXEC mode.
(Optional) Save your entries in the configuration file.
Purpose
Enter global configuration mode.
Enter router configuration mode.
Define an administrative distance.
weight—The administrative distance as an integer from
10 to 255. Used alone, weight specifies a default
administrative distance used when no other specification
exists for a routing information source. Routes with a
distance of 255 are not installed in the routing table.
(Optional) ip access list—An IP standard or extended
access list to be applied to incoming routing updates.
Return to privileged EXEC mode.
Display the default administrative distance for a
specified routing process.
(Optional) Save your entries in the configuration file.
Catalyst 3550 Multilayer Switch Software Configuration Guide
Table 31-16 on page 31-77 shows
31-87