Cisco Systems 3560-X, 3750-X Filtering Sources of Routing Information

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 42 Configuring IP Unicast Routing
Configuring Protocol-Independent Features
Beginning in privileged EXEC mode, follow these steps to control the advertising or processing of
routing updates:
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. Table 42-16 on page 42-92 shows
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 Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 router {bgp | rip | eigrp}Enter router configuration mode.
Step 3 distribute-list {access-list-number |
access-list-name} out [interface-name | routing
process | autonomous-system-number]
Permit or deny routes from being advertised in routing
updates, depending upon the action listed in the access list.
Step 4 distribute-list {access-list-number |
access-list-name} in [type-number]
Suppress processing in routes listed in updates.
Step 5 end Return to privileged EXEC mode.
Step 6 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 router {bgp | rip | ospf | eigrp}Enter router configuration mode.
Step 3 distance weight {ip-address {ip-address mask}}
[ip access list]
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.
Step 4 end Return to privileged EXEC mode.