BGP synchronization is the most difficult and confusing topic of the BGP. In this post i will try to explain BGP synchronization in a simple way. Basically synchronization is old loop prevention mechanism in BGP.
If synchronization is enabled on the BGP router, it will not advertise to ebgp neighbors or use the networks which are learnt from any of its IBGP neighbors, untill it gets the same network from IGP.
BGP synchronization is mandatory when there are routers running routing protocol other than BGP in the Autonomous system.
BGP synchronization can be disabled, if any one of the following condition matches,
1) If all the routers are running BGP protocol in the autonomous system
2) If AS is not working is transit AS ( if the AS is not passing the traffic from one AS to other AS).
In order to disable synchronization
Router(conf)# router bgp 100
Router(conf-router)# no synchronization
Note: By Default BGP synchronization is disabled on cisco routers which are having version 12.2(8) and latter
If synchronization is enabled on the BGP router, it will not advertise to ebgp neighbors or use the networks which are learnt from any of its IBGP neighbors, untill it gets the same network from IGP.
BGP synchronization is mandatory when there are routers running routing protocol other than BGP in the Autonomous system.
BGP synchronization can be disabled, if any one of the following condition matches,
1) If all the routers are running BGP protocol in the autonomous system
2) If AS is not working is transit AS ( if the AS is not passing the traffic from one AS to other AS).
In order to disable synchronization
Router(conf)# router bgp 100
Router(conf-router)# no synchronization
Note: By Default BGP synchronization is disabled on cisco routers which are having version 12.2(8) and latter
BGP follows a synchronization rule that states that all routers in transit AS, including non-bgp routers (like as, IGP routers), must learn of routes/prefixes, before BGP can advertise these routes to an eBGP neighbors! ...
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