BGP Overview Autonomous System Internet Service Provider BGP

BGP Overview Autonomous System Internet Service Provider • BGP used between autonomous systems (AS) • ISP BGP configuration can be complex

When Not to Use BGP Static A C B B Network number ISP runs BGP Advertise default network via IGP Use a static route to provide connectivity • Avoid BGP configuration by using default networks and static routes • Appropriate when the local policy is the same as the ISP policy

Policy Drives BGP Requirements BGP AS 100 BB AS 200 C BGP A BGP D AS 300 Static Route F AS 400 E • Policy for AS 100: Always use AS 300 path to reach AS 400

BGP Sessions AS 2 AS 1 EBGP IBGP Service Provider IBGP • BGP traffic is carried by TCP connections • Two types of BGP sessions: External and internal

BGP Operation IGP Routing Protocol IP BGP Routing Protocol • BGP routes can be redistributed into the IP routing table

BGP Commands Router(config)# router bgp autonomous-system • Enables the BGP routing protocol Router(config-router)# network-number • Allows BGP to advertise an IGP route if it is already in the IP table • Does not activate the protocol on an interface

BGP Commands (cont. ) Router(config-router)# neighbor ip-address remote-as autonomous-system • Activates a BGP session Router# clear ip bgp { * | address } • Resets BGP connections • Use after changing BGP configuration

BGP Configuration Example 19. 0. 0. 0 15. 1. 1. 0 AS 100 AS 200 A 15. 1. 1. 1 Configuration for A router bgp 100 network 19. 0. 0. 0 neighbor 15. 1. 1. 2 remote-as 200 B 15. 1. 1. 2 Configuration for B router bgp 200 network 15. 0. 0. 0 neighbor 15. 1. 1. 1 remote-as 100 • Representative of most BGP configurations

Mājas darbs #2 Salidzinat 2004. , 2003. un 2002. gada globalas BGP marsrutizacijas tabulas: 1. maršrutēto subnetu skaits, 2. neizmantoto A, B, C klases adresu skaits (adrese ir neizmantota, ja BGP tabula neparadas neviens tās subnets). Iekš 2004. gada tabulas noskaidrot: 1. trīs AS, kurām pieder vislielākais maršrutēto subnetu skaits (neatkarīgi no maskas garuma). 2. trīs IP subnetus, kas ir sasniedzami caur vislielāko tranzīta AS skaitu (skaitīt tikai atšķirīgos AS numurus iekš path)? Kam šie IP subneti pieder un kur ģeogrāfiski tie atrodas? 3. Kurš globalās BGP tabulas ieraksts apraksta routi uz jusu majas/darba/universitates datoru? Izmantojot 2004. gada tabulu, grafiski uzzimejiet savienojumus starp sekojošām AS (norādot arī tranzīta AS un visu iesaistīto AS numurus un vārdus): 1. AS, kurai pieder jusu dators, 2. Katra pasaules kontinenta atrodiet kadu WWW serveri, noskaidrojiet ta IP adresi, un attēlojiet AS kurai tas pieder.