Which option is true regarding the synchronization rule?
A.
Do not use or internally advertise a route until the route is learned from a source other than BGP.
B.
Do not use or advertise a route until the route is learned from a BGP peer.
C.
Do not use or advertise routes marked PARTIAL.
D.
Wait until a CONFIRM message is received before using routes from BGP neighbors.
Answer: A
Explanation
The complete synchronization rule is “A BGP router should not use, or advertise to an external neighbor, a route learned by IBGP, unless that route is local or is learned from the IGP.”
With the default of synchronization disabled, BGP can use and advertise to external BGP neighbors routes learned from an IBGP neighbor that are not present in the local routing table
The “synchronization” here means “synchronization between iBGP with its IGP (such as OSPF, EIGRP…)
You can disable synchronization if one of the following conditions is true:
Your AS does not pass traffic from one AS to another AS.
All the transit routers in your AS run BGP.
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