Border Gateway Protocol (BGP) is an interdomain routing protocol designed to provide loop-free routing between separate routing domains that contain independent routing policies (autonomous systems). The Cisco software implementation of BGP version 4 includes support for 4-byte autonomous system numbers and multiprotocol extensions to allow BGP to carry routing information for IP multicast routes and multiple Layer 3 protocol address families including IP Version 4 (IPv4), IP Version 6 (IPv6), Virtual Private Networks Version 4 (VPNv4), Connectionless Network Services (CLNS), and Layer 2 VPN (L2VPN). This module contains conceptual material to help you understand how BGP is implemented in Cisco software.

For more information, see Information About Cisco BGP.

• BGP-PIC is not supported.

  But by default, BGP-PIC is enabled on all the Cisco IOS XE platforms, hence the BGP-PIC must be disabled using the cef table output-chain build favor memory-utilization command under configuration mode. If the BGP-PIC is not disabled, then the route update failure might occur.

• When you configure BGP with graceful restart and remove the BGP configuration using no router bgp command, the graceful restart timer starts. As a result, the stale entry is present in the BGP routing table and it is only removed after the BGP graceful restart timer is over.