Refer to the exhibit. All routers are configured for BGP. EBGP routes received on router R2
show up in the BGP table on routers R1 and R3 but not in their IP routing tables. What
would cause this (Choose two) ?
A.
Synchronization in autonomous system 100 is turned is on.
B.
Synchronization in autonomous system 100 is turned is off.
C.
EBGP multihop is not configured on routers R1 and R3.
D.
Routers R1 and R3 do not receive the same routes via an IGP.
E.
The BGP routers in autonomous system 100 are not logically fully-meshed.
Explanation:
If your AS passes traffic from another AS to a third AS, BGP should not advertise a route
before all routers in your AS learn about the routevia IGP. BGP waits until IGP propagates
the route within the AS and then advertise it so external peers. A BGP router with
synchronization enabled does not install iBGP learned routes into the routing table if it is not
able to validate those routes in its IGP. Issue theno synchronization command under router
bgp in order to disable synchronization. This prevents BGP from validating iBGP routes in
IGP. In this scenario, the routers must learn of the same route via an IGP, or
synchronization should be turned off. Since this ASdoes not appear to be a transit AS, the
best solution would be to disable synchronization.
Reference: BGP Case Studies,
http://www.cisco.com/en/US/tech/tk365/
technologies_tech_note09186a00800c95bb.shtml#synch