Cisco 3560G 48TS Software Configuration Guide - Page 683

Chapter 30 Configuring IP Unicast Routing Configuring Protocol-Independent Features Use a network monitoring privileged EXEC command such as show ip ospf interface to verify the interfaces that you enabled as passive, or use the show ip interface privileged EXEC command to verify the interfaces that you enabled as active. To re-enable the sending of routing updates, use the no passive-interface interface-id router configuration command. The default keyword sets all interfaces as passive by default. You can then configure individual interfaces where you want adjacencies by using the no passive-interface router configuration command. The default keyword is useful in Internet service provider and large enterprise networks where many of the distribution routers have more than 200 interfaces. Controlling Advertising and Processing in Routing Updates You can use the distribute-list router configuration command with access control lists to suppress routes from being advertised in routing updates and to prevent other routers from learning one or more routes. When used in OSPF, this feature applies to only external routes, and you cannot specify an interface name. You can also use a distribute-list router configuration command to avoid processing certain routes listed in incoming updates. (This feature does not apply to OSPF.) Beginning in privileged EXEC mode, follow these steps to control the advertising or processing of routing updates: Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Command configure terminal router {bgp | rip | igrp | eigrp} distribute-list {access-list-number | access-list-name} out [interface-name | routing process | autonomous-system-number] distribute-list {access-list-number | access-list-name} in [type-number] end copy running-config startup-config 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. 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 30-13 on page 30-66 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. 78-16156-01 Catalyst 3560 Switch Software Configuration Guide 30-75