BGP Synchronization

What would be the next hop IP address for a network 170.10.0.0 advertise to RTC router by RTA router 
Next hop IP address would be 2.2.2.1

what is the next hop IP address for network 170.10.0.0 recevied by RTB from RTA router 

• RTA and RTB run IBGP
• The  next hop will be  2.2.2.1. 
• According to rule, next hop is carried via iBGP. 

For router RTB to reach network 170.10.0.0, where it must send traffic
In order to reach the 170.10.0.0, RTB must send the traffic to RTE.

What would happen if RTA has not redistributed network 170.10.0.0 into IGP.
A: RTE will have no idea that 170.10.0.0 even exists.

What would happen if router RTE has no idea of 170.10.0.0 network and RTB starts to advertise to AS400 that RTB can reach 170.10.0.0Traffic that comes from RTD to RTB with destination 170.10.0.0 flows in and drops at RTE.

What does Synchronization rule statesSynchronization states that, if your AS passes traffic from another AS to a third AS, BGP should not advertise a route before all the routers in your AS have learned about the route via IGP. BGP waits until IGP has propagated the route within the AS. Then, BGP advertises the route to external peers.

According to Synchronization rule, what must be handled carefully in the above network

• AS 100 is a transit AS 
• AS 100 passes traffic from AS 300 to AS 400 and vice versa.
• All the routers in AS 100 should know about network 170.10.0.0.
• When router RTA receives update about network 170.10.0.0, it should redistribute into IGP network. 
• When all routers has learned about network 170.10.0.0, router RTB can send update about 170.10.0.0 network to external AS 400
• RTB waits to hear about 170.10.0.0 via IGP. 
• Once RTB receives update for 170.10.0.0 network via IGP,it starts to send the update to RTD.
• We can make RTB think that IGP has propagated the information 
• If we add a static route in RTB that points to 170.10.0.0. Make sure that other routers can reach 170.10.0.0.

DISABLING SYNCHRONIZATION
Where we require to disable synchronization

• In case where AS does not work as transit As
• If all routers in  AS run BGP and no IGP protocol .

What is the benefits of disabling synchronizationAllows us to carry fewer routes in IGP and allow BGP to converge more quickly.

Does synchronization is disabled by defaultNo
Need to disable synchronization manually
After disabling synchronization,make sure to use clear ip bgp address command to reset the session.


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