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BGP Overview

Autonomous System. Internet Service Provider. BGP Overview. BGP used between autonomous systems (AS) ISP BGP configuration can be complex. Network number. Static. C. ISP runs BGP. A. B. B. Advertise default network via IGP. Use a static route to provide connectivity.

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BGP Overview

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  1. AutonomousSystem InternetServiceProvider BGP Overview • BGP used between autonomous systems (AS) • ISP BGP configuration can be complex

  2. Networknumber Static C ISP runs BGP A B B Advertise defaultnetwork via IGP Use a static route toprovide connectivity When Not to Use BGP • Avoid BGP configuration by using default networks and static routes • Appropriate when the local policy is the same as the ISP policy

  3. F Policy Drives BGP Requirements AS200 Static Route C B BGP B AS400 AS100 BGP A BGP AS300 • Policy for AS 100: Always use AS 300 path to reach AS 400 D E

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

  5. BGP Operation IGPRoutingProtocol BGPRoutingProtocol IP BGP • BGP routes can be redistributed into the IP routing table

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

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

  8. AS 100 AS 200 BGP Configuration Example 19.0.0.0 15.0.0.0 15.1.1.0 A B 15.1.1.1 15.1.1.2 Configuration for A Configuration for B • Representative of most BGP configurations router bgp 100network 19.0.0.0neighbor 15.1.1.2 remote-as 200 router bgp 200network 15.0.0.0neighbor 15.1.1.1 remote-as 100

  9. Mājas darbs #2 • Salidzinat 2004., 2003. un 2002.gada globalas BGP marsrutizacijas tabulas: • maršrutēto subnetu skaits, • neizmantoto A, B, C klases adresu skaits (adrese ir neizmantota, ja BGP tabula neparadas neviens tās subnets). • Iekš 2004.gada tabulas noskaidrot: • trīs AS, kurām pieder vislielākais maršrutēto subnetu skaits (neatkarīgi no maskas garuma). • 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? • 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): • AS, kurai pieder jusu dators, • Katra pasaules kontinenta atrodiet kadu WWW serveri, noskaidrojiet ta IP adresi, un attēlojiet AS kurai tas pieder.

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