BGP Fundamentals
Here you will find answers to BGP Fundamentals Questions
Question 1
Based on the topology diagram shown in the exhibit, when should BGP
be used as the routing protocol between the customer and the ISP?
A. If physical link failures can not be detected by the link-level procedures.
B. If the customer wants to affect how the ISP will route the customer’s traffic out to the rest of the Internet.
C. If the ISP does not support static routing with the customer.
D. If the customer is using provider-assigned (PA) addresses inside the customer’s network.
E. If the customer is using private addresses inside the customer’s network.
Answer: A
Question 2
Based on the network diagram shown in the exhibit, what is the
correct configuration on the customer edge router used to conditionally
announce the customer networks to the ISP?
A. router bgp 65001
! neighbor commands not shown
network 192.168.8.0 mask 255.255.252.0
!
ip route 192.168.8.0 255.255.252.0 192.168.8.33
B. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0 summary-only
!
ip route 192.168.8.0 255.255.252.0 192.168.8.33
C. router bgp 65001
! neighbor commands not shown
network 192.168.8.0
network 192.168.9.0
network 192.168.10.0
network 192.168.11.0
!
ip route 192.168.8.0 255.255.255.0 null0
ip route 192.168.9.0 255.255.255.0 null0
ip route 192.168.10.0 255.255.255.0 null0
ip route 192.168.11.0 255.255.255.0 null0
D. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0 summary-only
!
router ospf 1
network 192.168.8.0 0.0.3.255 area 0
E. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0
!
ip route 192.168.8.0 255.255.252.0 null0
Answer: A
Question 3
Which two statements about a transit AS are correct? (Choose two)
A. A transit AS has eBGP connection(s) to only one external AS.
B. Routes between ASs are always exchanged via eBGP.
C. A transit AS uses an IGP like OSPF or ISIS to propagate the external networks within the transit AS.
D. Core routers within a transit AS normally use default routing to reach the external networks.
E. iBGP sessions can be established between non directly connected routers.
Answer: B E
Question 4
Which command is used to configure the external, confederation-wide AS number?
A. router(config)#router bgp {as-number}
B. router(config-router)#bgp confederation peers {as-number}
C. router(config-router)#bgp confederation identifier {as-number}
D. router(config-router)#bgp cluster-id {as-number}
E. router(config-router)#neighbor {ip address} remote-as {as-number}
Answer: C
Question 5
In a Transit AS, how do the internal routers within the Transit AS
forward packets destined for the external networks using a scalable
solution?
A. using the default route
B. using the IGP routes where the external networks are redistributed into the IGP by the edge routers
C. using the EBGP routes where the external networks are redistributed into the IBGP by the edge routers
D. using the IBGP routes, then using recursive lookup based on IGP information to resolve the BGP next-hop
Answer: D
Question 6
Given the following configurations, R2 and R3 are not able to
successfully establish the iBGP session using the loopback 0 interfaces.
What could be the cause of this problem?
hostname R2
!
interface loopback 0
ip address 2.2.2.2
!
interface e0
ip address 10.1.1.1 255.255.255.0
no shut
!
interface e1
ip address 10.2.2.1 255.255.255.0
no shut
!
router bgp 65101
neighbor 172.16.1.1 remote-as 65100
neighbor 3.3.3.3 remote-as 65101
!
router eigrp 101
network 10.0.0.0
network 2.0.0.0
!
!
output omitted
!
hostname R3
!
interface loopback 0
ip address 3.3.3.3
!
interface e0
ip address 10.1.1.2 255.255.255.0
no shut
!
interface e1
ip address 10.2.2.2 255.255.255.0
no shut
!
router bgp 65101
neighbor 192.168.1.1 remote-as 65102
neighbor 2.2.2.2 remote-as 65101
!
router eigrp 101
network 10.0.0.0
network 3.0.0.0
!
A. The “No Sync” BGP configuration command is missing.
B. R2 and R3 are not using the loopback0 IP address as the source address for the BGP messages to each other.
C. The “network 2.0.0.0″ BGP configuration command is missing on R2 and
the “network 3.0.0.0″ BGP configuration command is missing on R3.
D. The “neighbor 2.2.2.2 ibgp-multihop 2″ BGP configuration command is
missing on R3 and the “neighbor 3.3.3.3 ibgp-multihop 2″ BGP
configuration command is missing on R2.
Answer: B
Question 7
What are two purposes of the BGP scan-time command? (Choose two)
A. to tune the BGP process which walks the BGP table and confirms the reachability of next hops
B. to allow faster detection of downed BGP peers
C. to improve BGP convergence time
D. to tune the BGP update interval
E. to decrease the effects of unstable routes by increasing the route suppression time
Answer: A C
Question 8
If there is no exact match in the local routing table, what three
conditions would result in BGP introducing the classful network
172.0.0.0 with the mask 255.0.0.0 into the BGP table? (Choose three)
A. no auto-summary is configured under the router bgp {as no.} command
B. network 172.0.0.0 is configured under the router bgp {as no.} command
C. any classful network must exist in the BGP table
D. auto-summary is enabled under the router bgp {as no.} command
E. the routing table contains the subnet 172.172.172.0 with a subnet mask of 255.255.255.0
F. a classless network must exist in the BGP table
Answer: B D E