736 BigIron RX Series Configuration Guide53-1001986-01Brocade implementation of BGP426BGP4 Router A sends a Hold Time of 5 seconds and BGP4 Router B sends a Hold Time of 4seconds, both routers use 4 seconds as the Hold Time for their BGP4 session. The default HoldTime is 180 seconds. Generally, the Hold Time is configured to three times the value of the KeepAlive Time.If the Hold Time is 0, a BGP4 router assumes that its neighbor is alive regardless of how manyseconds pass between receipt of UPDATE or KEEPALIVE messages.NOTIFICATION messageWhen you close the router’s BGP4 session with a neighbor, or the router detects an error in amessage received from the neighbor, or an error occurs on the router, the router sends aNOTIFICATION message to the neighbor. No further communication takes place between the BGP4router that sent the NOTIFICATION and the neighbors that received the NOTIFICATION.REFRESH messageBGP sends a REFRESH message to a neighbor to request the neighbor to resend route updates.This type of message can be useful if an inbound route filtering policy has been changed.Brocade implementation of BGP4BGP4 is described in RFC 1771 and the latest BGP drafts. The Brocade implementation fullycomplies with RFC 1771 and also supports the following:• RFC 1745 (OSPF Interactions)• RFC 1997 (BGP Communities Attributes)• RFC 2385 (TCP MD5 Signature Option)• RFC 2439 (Route Flap Dampening)• RFC 2796 (Route Reflection)• RFC 2842 and 3392 (Capability Advertisement)• RFC 3065 (BGP4 Confederations)• RFC 2858 (Multiprotocol Extensions)• RFC 2918 (Route Refresh Capability)• RFC 3392 (BGP Capability Advertisement)Memory considerationsBGP4 handles a very large number of routes and therefore requires a lot of memory. For example,in a typical configuration with just a single BGP4 neighbor, a BGP4 router may need to be able tohold up to 150,000 routes. Many configurations, especially those involving more than oneneighbor, can require the router to hold even more routes. The device provide dynamic memoryallocation for BGP4 data. These devices automatically allocate memory when needed to supportBGP4 neighbors, routes, and route attribute entries. Dynamic memory allocation is performedautomatically by the software and does not require a reload.
