Understanding iBGP vs. eBGP

  • iBGP is used when two BGP neighbors are established within the same AS.
  • eBGP is where neighbors are formed between two routers in different Autonomous Systems.
  • BGP Neighbors are not necessarily directly connected.  BGP sits on top of your existing internal structure – IGP or static routes.
  • Example of a “Transit AS” is where routes are advertised in to your AS from one ISP and advertised out by you to another ISP via BGP.
  • To avoid BGP blackholes, there are three solutions: – redistribute BGP routes into IGP (NOT recommended given size of BGP table), run BGP in some form on the Internal network or directly connect the two BGP neighbors.

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