Exhibit

What can prevent the corresponding BGP session from being successfully established?

A.
CK2 and CK5 cannot establish the IBGP session if the BGP Hello Timer between the two IBGP neighbors is different.

B.
CK1 and CK2 cannot establish the EBGP session if the BGP Hello Timer between the two EBGP neighbors are different.

C.
CK1 and CK2 cannot establish the EBGP session using the loopback0 interface if the EBGP-mutlihop value is set to 2.

D.
CK2 and CK5 cannot establish the IBGP session because they are not using the loopback0 interface to establish the IBGP session.

E.
CK2 and CK5 cannot establish the IBGP session if CK3 and CK4 have an access list permitting only TCP port 80 and IP protocol number 89 traffic.

Explanation:
Wrong Answers
A Hello timers can be different. Use caution
B Hello Timers can be different. Use caution.
C By default EBGP has multi-hop of 1. Without a multi-hop of 2 a connection can not be established
D If between R2 and R5 will work as long as Links are up. The sessions will succeed no matter how it is configured. The catch is when the link breaks then the session may or may not fail. It would be best to use a loopback.
Correct Answer
E TCP for 179 is used by BGP. BGP session is routed through the IGP (OSPF). This means by default traffic between CK2 and CK5 will route through CK4, because CK4 has the lowest cost path. However if only ports 80 and 89 are allowed 179 will not work.