- 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. Comment with corrections, please.