Refer to the exhibit.

It is desired to set up a BGP neighbor relationship between routers R1 and R4. BGP packets
between them could travel through R2 or R3. What is the simplest configuration that will allow for
failover?

A.
Configure BGP neighbor relationships between all interfaces on R1 and R4

B.
Install a direct connection between R1 and R4.

C.
Configure loopback interfaces on R1 and R4 to provide the update source address for BGP
packets.

D.
Configure only one neighbor relationship between R1’s 192.168.1.2 interface and R4’s
172.16.10.2 interface.

Explanation:
Assume R4 only uses this configuration:
R4(config)#router bgp 65000R4(config-router)#neighbor 192.168.1.2 remote-as 65000
Then if R1 sends BGP packets to R4 via R3, the source IP address of the packets is 192.168.2.2.
But R4 does not recognize this IP address because 192.168.2.2 is not configured in the “neighbor”
command of R4. Therefore the IBGP session between R1 & R4 is not established -> these packets will be dropped.

The simplest configuration to allow R1 and R4 communicate via both R2 & R3 is to use a loopback
interface address rather than a physical interface address as the source IP address for all BGP
packets. To do this, use the command:
R4(config-router)#neighbor 1.1.1.1 update-source loopback0
(In which 1.1.1.1 is the loopback interface of R1). In practical, we should establish neighborship
with the loopback interface rather than the physical interface because if the physical interface goes
down, the neighborship would be lost while a loopback interface never goes down.
Also, when configuring “1.1.1.1 as the neighbor, you must configure on R1 the “neighbor 4.4.4.4
update-source loopback0” command so that the source IP address of packets sent from R1
(loopback0 – 1.1.1.1) will be matched with the neighbor command configured on R4.