Cisco 3560G 48TS Software Configuration Guide - Page 657

Chapter 30 Configuring IP Unicast Routing Configuring BGP Anything other than state = established means that the peers are not running. The remote router ID is the highest IP address on that router (or the highest loopback interface). Each time the table is updated with new information, the table version number increments. A table version number that continually increments means that a route is flapping, causing continual routing updates. For exterior protocols, a reference to an IP network from the network router configuration command controls only which networks are advertised. This is in contrast to Interior Gateway Protocols (IGPs), such as IGRP, which also use the network command to determine where to send updates. For detailed descriptions of BGP configuration, refer to the "Configuring BGP" chapter in the Cisco IOS IP and IP Routing Configuration Guide. For details about specific commands, refer to the Cisco IOS IP and IP Routing Command Reference for Release 12.1. See Appendix C, "Unsupported Commands in Cisco IOS Release 12.1(19)EA1," for a list of BGP commands that are visible but not supported by the switch. Managing Routing Policy Changes Routing policies for a peer include all the configurations that might affect inbound or outbound routing table updates. When you have defined two routers as BGP neighbors, they form a BGP connection and exchange routing information. If you later change a BGP filter, weight, distance, version, or timer, or make a similar configuration change, you must reset the BGP sessions so that the configuration changes take effect. There are two types of reset, hard reset and soft reset. Cisco IOS software releases 12.1 and later support a soft reset without any prior configuration. To use a soft reset without preconfiguration, both BGP peers must support the soft route refresh capability, which is advertised in the OPEN message sent when the peers establish a TCP session. A soft reset allows the dynamic exchange of route refresh requests and routing information between BGP routers and the subsequent re-advertisement of the respective outbound routing table. • When soft reset generates inbound updates from a neighbor, it is called dynamic inbound soft reset. • When soft reset sends a set of updates to a neighbor, it is called outbound soft reset. A soft inbound reset causes the new inbound policy to take effect. A soft outbound reset causes the new local outbound policy to take effect without resetting the BGP session. As a new set of updates is sent during outbound policy reset, a new inbound policy can also take effect. Table 30-11 lists the advantages and disadvantages hard reset and soft reset. Table 30-11 Advantages and Disadvantages of Hard and Soft Resets Type of Reset Advantages Disadvantages Hard reset No memory overhead The prefixes in the BGP, IP, and FIB tables provided by the neighbor are lost. Not recommended. Outbound soft reset No configuration, no storing of routing table Does not reset inbound routing table updates. updates Dynamic inbound soft reset Does not clear the BGP session and cache Both BGP routers must support the route Does not require storing of routing table updates refresh capability (in Cisco IOS Release 12.1 and has no memory overhead and later). 78-16156-01 Catalyst 3560 Switch Software Configuration Guide 30-49