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.

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