Filtering Sources Of Routing Information - Cisco Catalyst 3750 Software Configuration Manual

Configuring Protocol-Independent Features
Beginning in privileged EXEC mode, follow these steps to control the advertising or processing of
routing updates:
Command
Step 1 configure terminal
Step 2
router {bgp | eigrp | igrp | isis | iso-igrp | ospf | rip} Enter router configuration mode.
Step 3
distribute-list {access-list-number |
access-list-name} out [interface-name | routing
process | autonomous-system-number]
Step 4
distribute-list {access-list-number |
access-list-name} in [type-number]
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 | eigrp | igrp | isis | iso-igrp | ospf | rip}
Step 3 distance weight {ip-address {ip-address mask}}
[ip access list]
Step 4
end
Catalyst 3750 Metro Switch Software Configuration Guide
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Chapter 28
Purpose
Enter global 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.
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 that is 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.
Configuring IP Unicast Routing
Table 28-18 on page 28-89
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