BGP Notes – Synchronization

  • With synchronization on, route must be synchronized to an IGP in order for that routes to be able to be voted ‘best” by BGP.
    • That means the exact route must already be in the routing table via an IGP.
    • Static routes don’t count.
    • This is traditionally accomplished by redistributing BGP routes into an IGP.
    • With today’s Internet prefix count over 350k, this may not be such a good idea in some situations.
    • Synchronization is off by default.
  • Synchronization prevents black hole routes from being advertised via iBGP.
    • Unless every router is participating in iBGP, there’s no guarantee that any one router will have a route to NEXT_HOP.
  • Synchronization also prevents a router from advertising the black hole to an eBGP neighbor.
    • You don’t want to tell the world you have a path to a prefix when you really have a !N.
  • Synchronization can be safely disabled with the use of route reflectors or confederations.


These are just some notes I’ve been taking. ┬áComment with corrections, please.

Aaron Conaway

I shake my head around sometimes and see what falls out. That's what lands on these pages. If you have any questions, the best way to contact me is through Twitter at @aconaway.

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