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 with the mask into the BGP
table? (Choose three.)

  • A. the routing table contains the subnet with a subnet mask of
  • B. network 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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