Border Gateway Protocol (BGP) - Introduction

Protocol Classification Review

• IGP

• EGP

• BGP is not quick and is usually not implemented internally

BGP: The Protocol of the Internet

• Distance Vector
  • Each network is effectively an autonomous system
  • Networks connect to each other
  • Hops are typically routers, but here we care about automated systems, how many networks do I have to cross?
• Autonomous Systems
• iBGP
  • internal
• eBGP
  • external
• Built for scalability
  • Handling hundreds of thousands of hosts
• Tunable through policy
  • BGP does not consider speed, it only considers hop count.

BGP Scalability

• In January 2021, per the CIDR report, the table stood at around 861, 418 IPv4 prefixes
• Cisco recommends a minimum of 512 MB of RAM in the router to store a complete global BGP routing table from one BGP peer.
  • You can pull partial tables as well as full tables.

Provider Independent Addressing

• Do you have Provider Independent Addresses (PI addresses)?
• IP addresses can be borrowed from an Internet Service Provider
  • You can actually purchase a block of IP addresses
• IP addresses can be purchased and owned outright
• Your IP block must be announced to the world via BGP

Full vs. Partial Tables

• BGP tables consume RAM
• Pulling tables from multiple peers facilitates better decisions
• It may be appropriate to load partial tables
  • We can make good desisions with partial tables, not the best but still good.

BGP Peering

• Announce PI Addresses to the world
• If they accept those, they will bring into their routers and will tell to the rest of the internet
• We typically connect with multiple service providers.

• If we got lots of memory we can pull tables for both sides and we can do better discussions than pulling from one side.
• iBGP neighbor are routers under our control
• eBGP neighbor are those with which we can exchange routes from external BGP networks.
• Some service providers let you look at their providers tables