642-661 Configuring BGP on Cisco Routers Exam

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Question 1

External BGP peers must normally reside on a directly connected network. Sometimes it is
useful to relax this restriction to enable load balancing. Which neighbor command option is
used to permit this?

  • A. ebgp-multihop
  • B. soft-reconfiguration
  • C. remote-as
  • D. send-community
  • E. no sync
  • F. next-hop-self


Answer : A

Question 2

What is the correct command to set the BGP scanner interval to two minutes?

  • A. The maximum scanning interval cannot exceed one minute.
  • B. bgp scan-time 2
  • C. bgp scan-time 120
  • D. bgp scan-time 2 60


Answer : A

Question 3

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. the routing table contains the subnet 172.172.172.0 with a subnet mask of 255.255.255.0
  • B. network 172.0.0.0 is configured under the router bgp {as no.} command
  • C. no auto-summary is configured under the router bgp {as no.} command
  • D. any classful network must exist in the BGP table
  • E. auto-summary is enabled under the router bgp {as no.} command
  • F. a classless network must exist in the BGP table


Answer : A,B,E

Question 4

Which statement is correct when utilizing the BGP TTL security check feature?

  • A. It eliminates the need for BGP keepalive packets.
  • B. It is configured locally for each eBGP peering session.
  • C. It generates a syslog error if a "forged" packet is received.
  • D. It is not functional on multihop BGP peering sessions.
  • E. It compares the value of the received packet TTL against a BGP interface Access-List.


Answer : B

Question 5

What are two characteristics of BGP confederations? (Choose two.)

  • A. All routers within the BGP confederation must support BGP confederations.
  • B. An Intra-Confederation EBGP session behaves like an EBGP session when propagating routing updates.
  • C. The member AS numbers used within the confederation are visible from outside the confederation.
  • D. Intra-Confederation EBGP neighbors must be directly connected or ebgp-multihop must be configured.


Answer : A,D

Question 6

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 7

Which BGP configuration option is designed to reduce router processing load caused by
unstable routes?

  • A. bgp dampening
  • B. no sync
  • C. neighbor {ip-address} maximum-prefix {number}
  • D. sync
  • E. bgp scan-time
  • F. bgp deterministic-med


Answer : A

Question 8

Which two of the following are true regarding the BGP Prefix-Based outbound route filtering
feature? (Choose two.)

  • A. Outbound route filtering is more effective when a distance vector IGP is used.
  • B. Outbound route filtering can be configured for either iBGP or eBGP sessions.
  • C. The outbound route filter can be defined in a Prefix list, Distribute list or Access lists.
  • D. Outbound route filtering is configured only on a per-address family basis.
  • E. IP multicast routes are not supported.


Answer : D,E

Question 9

Look at the picture.




Answer :

Question 10

Why can using the ip tcp path-mtu-discovery command improve BGP convergence?

  • A. Smaller MSS sizes may reduce BGP convergence times.
  • B. BGP is enabled to fragment its large update packets.
  • C. The BGP memory requirements on routers are reduced.
  • D. Single packet sizes in TCP sessions are limited.
  • E. BGP is allowed to use a larger TCP window size.


Answer : E

Question 11

Examine the topology and the configuration output. If the show ip bgp summary command
was issued from R1, how many prefixes would it have in the State/PfxRcd field?


  • A. 1
  • B. 0
  • C. 3
  • D. 2


Answer : B

Question 12

What is the maximum number of parallel routes that can be injected into the routing table
when using the iBGP multipath load sharing feature?

  • A. The number of parallel paths injected into the routing table will depend on the IGP currently in use within the iBGP domain.
  • B. iBGP multipath can support up to 4 parallel paths.
  • C. None, multipath is supported on eBGP only when used in conjunction with the update- source command.
  • D. iBGP multipath can support up to 6 parallel paths.
  • E. The maximum number of parallel paths injected into the routing table is specified by BGP MED and ranges from 2 to 256 parallel paths.


Answer : D

Question 13

How does the extended community cost feature influence the BGP best path selection?

  • A. inserts the cost attribute after the MED attribute comparison, forcing best path route selection if all other preferred route selection criteria are equal
  • B. selects the BGP route with the highest attached extended community cost value
  • C. alters the BGP AS exit path selection by adding the link cost to the local preference
  • D. acts as a best path "tie breaker" when multiple IGP equal cost paths occur
  • E. reflects the bandwidth of links entering the local AS from eBGP neighbors (in the MED attribute)


Answer : D

Question 14

Which command allows IBGP to scale within an AS?

  • A. neighbor {ip-address} route-reflector-client
  • B. neighbor {ip-address} next-hop-self
  • C. neighbor {ip-address} update-source loopback0
  • D. neighbor {ip-address} remote-as {confederation-id}
  • E. no sync
  • F. neighbor {ip-address} ebgp-multihop 2


Answer : A

Question 15

Which one of these statements regarding intraconfederation EBGP sessions is correct?

  • A. Member-AS numbers are removed when a router sends a BGP update over an intraconfederation EBGP session.
  • B. An intraconfederation EBGP session behaves like an IBGP session when propagating routing updates.
  • C. Updates from an intraconfederation EBGP neighbor are subject to the BGP split horizon rule.
  • D. Intraconfederation EBGP sessions must be established over loopback interfaces.
  • E. Intraconfederation EBGP neighbors must be directly connected.


Answer : B

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