BGP synchronization rules

The BGP synchronization rules only apply to iBGP.

If your autonomous system is passing traffic from another AS to a third AS, BGP should not advertise a route before all routers in your AS have learned about the route via IGP.

BGP will wait until the IGP has propagated the route within the AS and then it will advertise that route to external peers.

If you will not be passing traffic from a different autonomous system through your AS, or if all routers in your AS will be running BGP, you can disable synchronization. Disabling this feature can allow you to carry fewer routes in your IGP and allow BGP to converge more quickly.

The IGP routing table MUST be synchronized with iBGP routing table.

This can happen only if the eBGP learned routes are redistributed in an IGP such as OSPF at the ASBR to advertise routes that are not already in the routing table with the IGP. The matching route/mask must be in the routing table.

It's not needed if:

• all router in AS run BGP
• AS is not a transit AS [does not forward between other AS]

 router bgp 65109
   no synchronization
   bgp router-id 10.3.3.3
   network 192.168.10.0 mask 255.255.255.252
   network 192.168.10.4 mask 255.255.255.252
   neighbor 192.168.10.1 remote-as 100
   neighbor 192.168.10.6 remote-as 200

• In order for iBGP to work, Peers must be fully meshed or routes must be redistributed into and synchronized with an IGP.
• If the IBGP peers are fully meshed, synchronization must be disabled in order to inject routes learned from eBGP into the routing table as it traverses the IBGP group.