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Border Gateway Protocol (BGP4)

Border Gateway Protocol (BGP4). Rizwan Rehman, CCS, DU. Border Gateway Protocol (BGP). Routing/Forwarding basics Building blocks Exercises BGP protocol basics Exercises BGP path attributes Best path computation Exercises. Autonomous System (AS). Collection of networks with same policy

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Border Gateway Protocol (BGP4)

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  1. Border Gateway Protocol (BGP4) Rizwan Rehman, CCS, DU

  2. Border Gateway Protocol (BGP) • Routing/Forwarding basics • Building blocks • Exercises • BGP protocol basics • Exercises • BGP path attributes • Best path computation • Exercises

  3. Autonomous System (AS) • Collection of networks with same policy • Single routing protocol • Usually under single administrative control • IGP to provide internal connectivity AS 100

  4. Autonomous System(AS)... • Identified by ‘AS number’ • Public & Private AS numbers • Examples: • Service provider • Multi-homed customers • Anyone needing policy discrimination

  5. Routing flow and packet flow packet flow egress announce accept AS2 AS 1 Routingflow announce accept ingress • For networks in AS1 and AS2 to communicate: AS1 must announce routes to AS2 AS2 must accept routes from AS1 AS2 must announce routes to AS1 AS1 must accept routes from AS2 packet flow

  6. Egress Traffic • Packets exiting the network • Based on • Route availability (what others send you) • Route acceptance (what you accept from others) • Policy and tuning (what you do with routes from others) • Peering and transit agreements

  7. Ingress Traffic • Packets entering your network • Ingress traffic depends on: • What information you send and to who • Based on your addressing and ASes • Based on others’ policy (what they accept from you and what they do with it)

  8. Types of Routes • Static Routes • configured manually • Connected Routes • created automatically when an interface is ‘up’ • Interior Routes • Routes within an AS • Exterior Routes • Routes exterior to AS

  9. What Is an IGP? • Interior Gateway Protocol • Within an Autonomous System • Carries information about internal prefixes • Examples—OSPF, ISIS, EIGRP…

  10. What Is an EGP? • Exterior Gateway Protocol • Used to convey routing information between ASes • De-coupled from the IGP • Current EGP is BGP4

  11. Why Do We Need an EGP? • Scaling to large network • Hierarchy • Limit scope of failure • Define administrative boundary • Policy • Control reachability to prefixes

  12. Interior vs. Exterior Routing Protocols • Interior • Automatic discovery • Generally trust your IGP routers • Routes go to all IGP routers • Exterior • Specifically configured peers • Connecting with outside networks • Set administrative boundaries

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