BGP (Border Gateway Protocol)

Quick Overview

• BGP is an exterior routing protocol commonly used to enable networks on the internet to
  • BGP is a very scalable routing protocol and was developed for this purpose. communicate.
• BGP uses the TCP Port 179.
• Administration of BGP eg. managing bandwidth or other attributes is much easier than for interior protocols like OSPF or EIGRP.
• BGP is a path vector protocol and advertises paths to destinations rather than just distances.

Quick overview of BGP packets

• Open
  • Like OSPF hello packets
• Update
  • NLRI (Network Layer Reachability Information) - Refers to the network addresses / prefixes being advertised.
  • BGP Path Attributes
    • Carries each ASN per hop. Eg. Going from ASN 1 to 13 to 15 would format like this:
      • PA:AS-Path=15 13 1
• Keepalive
• Notification
• Route-refresh

BGP Introductory Configuration

Starting BGP configuration

• R1(config)#router bgp 1
  • 1 = the autonomous system number (like OSPF areas)

Configuring a network to advertise

• R1(config-router)#network xxx.xxx.xxx.xxx mask xxx.xxx.xxx.xxx

Configuring a BGP neighbor

• `R1(config-router)#neighbor xxx.xxx.xxx.xxx
• `R1(config)#network xxx.xxx.xxx.xxx

BGP show commands

• L1(config-if)#do show bgp ipv4 unicast summary
  • Writes an overall summary of BGP statistics