Cisco 642-885 Online Practice Questions and Exam Preparation

Cisco 642-885 Online Questions & Answers

• Question 11:

  With IPv6 multicast, which feature can be used as a replacement method for static RP configuration?

  A. PIM Snooping
  B. MLD
  C. MLD Snooping
  D. Embedded RP
  E. DHCPv6
  D. Embedded RP

• Question 12:

  Which two statements correctly describe the RPF check when a multicast packet arrives at a router? (Choose two.)

  A. The router looks up the source address in the unicast routing table to determine if the packet has arrived on the interface that is on the reverse path back to the source
  B. The router looks up the destination address in the unicast routing table to determine if the packet has arrived on the interface that is on the reverse path back to the destination
  C. If the packet has arrived on the interface leading back to the destination, the RPF check passes and the packet is forwarded. If the RPF check fails, the packet is dropped
  D. If the packet has arrived on the interface leading back to the source, the RPF check passes and the packet is forwarded. If the RPF check fails, the packet is dropped
  A. The router looks up the source address in the unicast routing table to determine if the packet has arrived on the interface that is on the reverse path back to the source
  D. If the packet has arrived on the interface leading back to the source, the RPF check passes and the packet is forwarded. If the RPF check fails, the packet is dropped

  ---

  Reverse Path Forwarding (RPF)

  RPF is a fundamental concept in multicast routing that enables routers to correctly forward multicast traffic down the distribution tree. RPF makes use of the

  existing unicast routing table to determine the upstream and downstream neighbors. A router will only forward a multicast packet if it is received on the upstream

  interface.

  This RPF check helps to guarantee that the distribution tree will be loop free.

  RPF Check

  When a multicast packet arrives at a router, the router will perform an RPF check on the packet. If the RPF check is successful, the packet will be forwarded.

  Otherwise it will be dropped. For traffic flowing down a source tree, the RPF check procedure works as follows:

  Step 1. Router looks up the source address in the unicast routing table to determine if it has arrived on the interface that is on the reverse path back to the source.

  Step 2. If packet has arrived on the interface leading back to the source, the RPF check is successful and the packet will be forwarded.

  Step 3. If the RPF check in 2 fails, the packet is dropped.

• Question 13:

  What is determined by running the same hash algorithm on all PIMv2 routers?

  A. The SPT from the RP to the multicast source
  B. The SPT from the last hop router to the multicast source
  C. Auto RP election
  D. Which BSR to use for a particular multicast group
  E. Which RP to use from a set of candidate RPs in the RP set
  E. Which RP to use from a set of candidate RPs in the RP set

  ---

  

• Question 14:

  In which three cases is a dual-stack IPv6/IPv4 router required? (Choose three.)

  A. tunnel endpoint routers in the case of IPv6 over GRE
  B. transit routers in case of an IPv6 over GRE implementation
  C. 6to4 implementation border routers
  D. 6to4 implementation border and neighboring routers
  E. PE routers in case of an IPv6 over IPv4 tunnel over MPLS implementation
  F. PE and P routers in case of an IPv6 over IPv4 tunnel over MPLS implementation
  A. tunnel endpoint routers in the case of IPv6 over GRE
  C. 6to4 implementation border routers
  E. PE routers in case of an IPv6 over IPv4 tunnel over MPLS implementation

• Question 15:

  Refer to the exhibit.

  

  Given the partial BGP configuration, which configuration correctly completes the Cisco IOS-XR route reflector configuration where both the 1.1.1.1 and 2.2.2.2 routers are the clients and the 3.3.3.3 router is a non-client IBGP peer?

  A. neighbor 1.1.1.1 remote-as 65123 route-reflector-client neighbor 2.2.2.2 remote-as 65123 route-reflector-client neighbor 3.3.3.3 remote-as 65123
  B. neighbor 1.1.1.1 address-family ipv4 unicast remote-as 65123 route-reflector-client neighbor 2.2.2.2 address-family ipv4 unicast remote-as 65123 route-reflector-client neighbor 3.3.3.3 address-family ipv4 unicast remote-as 65123
  C. neighbor 1.1.1.1 remote-as 65123 address-family ipv4 unicast route-reflector-client neighbor 2.2.2.2 remote-as 65123 address-family ipv4 unicast route-reflector-client neighbor 3.3.3.3 remote-as 65123
  D. neighbor 1.1.1.1 remote-as 65123 neighbor 1.1.1.1 route-reflector-client neighbor 2.2.2.2 remote-as 65123 neighbor 2.2.2.2 route-reflector-client neighbor 3.3.3.3 remote-as 65123
  C. neighbor 1.1.1.1 remote-as 65123 address-family ipv4 unicast route-reflector-client neighbor 2.2.2.2 remote-as 65123 address-family ipv4 unicast route-reflector-client neighbor 3.3.3.3 remote-as 65123

• Question 16:

  Which command set should be used for a 6to4 tunnel in a Cisco IOS XE router, considering the border interface with IPv4 address of 209.165.201.2?

  A. interface Tunnel2002 ipv6 enable ipv6 address 2002:D1A5:C902::1/128 tunnel source Ethernet0/0 tunnel mode ipv6ip 6to4
  B. interface Tunnel2002 ipv6 enable ipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0 tunnel mode ipv6ip 6to4
  C. interface Tunnel2002 ipv6 enable ipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0 tunnel mode ipv6ip
  D. interface Tunnel2002 ipv6 enable ipv6 address 2002:D1A5:C902::1/128 tunnel source Ethernet0/0 tunnel mode ipv6ip auto-tunnel
  E. interface Tunnel2002 ipv6 enableipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0 tunnel mode ipv6ip auto-tunnel
  B. interface Tunnel2002 ipv6 enable ipv6 address 2002:D1A5:D902::1/128 tunnel source Ethernet0/0 tunnel mode ipv6ip 6to4

• Question 17:

  Refer to the exhibit for the outputs from an ASR9K router.

  

  Why did the ping fail?

  A. The ping command is missing the ipv6 option: ping ipv6 2001:db8:10:1:10::1/128
  B. There is a problem with the IS-IS configurations
  C. The fe80::eab7:48ff:fe2c:a180 next-hop is not reachable
  D. The prefix length should be removed from the IPv6 address in the ping command: ping ipv6 2001:db8:10:1:10::1
  E. IPv6 is not enabled on the Gi0/0/0/0 interface
  F. The IPv6 neighbor discovery protocol is not enabled on the Gi0/0/0/0 interface
  D. The prefix length should be removed from the IPv6 address in the ping command: ping ipv6 2001:db8:10:1:10::1

• Question 18:

  Refer to the exhibit.

  

  Which statement correctly explains the bgp graceful-restart command?

  A. This command is used to enable NSR and is entered on the NSR-capable router, and also on any NSR-aware peer
  B. This command is used to enable NSF and is entered on the NSF-capable router, and also on any NSF-aware peer
  C. This command is only required on the NSF-capable routers to enable BGP graceful restart with the BGP peers
  D. This command is only required on the NSF-aware routers to enable BGP graceful restart with the BGP peers
  E. This command is only required on the NSR-capable routers to enable BGP graceful restart with the BGP peers
  B. This command is used to enable NSF and is entered on the NSF-capable router, and also on any NSF-aware peer

  ---

  Graceful restart is supported in recent versions of Cisco IOS software (12.0S) and is supported in Cisco IOS XR software. Graceful restart is the mechanism by which BGP routing peers avoid changes to their forwarding paths following a switchover. If the BGP peer has received this capability, it is aware that the device sending the message is nonstop forwarding (NSF)-capable. Both the NSF-capable router and its BGP peers (NSFaware peers) need to exchange the graceful restart capability in their OPEN messages, at the time of session establishment. If both peers do not exchange the graceful restart capability, the session will not be graceful restart-capable. If the BGP session is lost during a Route Processor (RP) switchover or BGP process restart, the NSF-aware BGP peer marks all the routes associated with the NSF-capable router as stale; however, it continues to use these routes to make forwarding decisions for a set period of time. This functionality means that no packets are lost while the newly active RP is waiting for convergence of the routing information with its BGP peers.

  After a failover event occurs, the NSF-capable router reestablishes the session with the BGP peer. In establishing the new session, it sends a new graceful restart message that identifies the NSF-capable router as having restarted. At this point, the routing information is exchanged between the two BGP peers. Once this exchange is complete, the NSF-capable device uses the newly received routing information to update the RIB and the Forwarding Information Base (FIB) with the new forwarding information. The NSF-aware device uses the network information to remove stale routes from its BGP table. The BGP protocol is then fully converged. If a BGP peer does not support the graceful restart capability, it will ignore the graceful restart capability in an OPEN message but will establish a BGP session with the NSF-capable device. This functionality will allow interoperability with non-NSF-aware BGP peers (and without NSF functionality), but the BGP session with non- NSF-aware BGP peers will not be graceful restart- capable.

• Question 19:

  

  

  Which three statements regarding the BGP operations are correct? (Choose three)

  A. PE5 will set the local preferences 200 on all the prefixes sent to CE5
  B. PE5 will set the local preference to 200 on all the prefixes learned from CE5
  C. CE5 has received 5 prefixes from the PE5 EBGP peer
  D. CE5 has the BGP scan interval set to 30 seconds
  E. CE5 is announcing the 192.168.55.0/24 prefix via EBGP to the PE5 EBGP peer
  F. The AS-Path to reach the 209.165.202.128/27 prefix from CE5 is: 64500 64497 64498
  C. CE5 has received 5 prefixes from the PE5 EBGP peer
  E. CE5 is announcing the 192.168.55.0/24 prefix via EBGP to the PE5 EBGP peer
  F. The AS-Path to reach the 209.165.202.128/27 prefix from CE5 is: 64500 64497 64498

  ---

  # sh ip bgp | be Network #sh ip bgp # show ip bgp neighbors

• Question 20:

  Which four statements are correct regarding MSDP configurations and operations? (Choose four.)

  A. The MSDP peers are also typically the RPs in respective routing domains.
  B. SA messages are flooded to all other MSDP peers without any restrictions
  C. On Cisco IOS, IOS-XE, and IOS-XR, the router can be configured to cache the SA messages to reduce the join latency
  D. SA messages are used to advertise active sources in a domain
  E. MSDP establishes neighbor relationships with other MSDP peers using TCP port 639
  F. MSDP peerings on Cisco IOS, IOS-XE, and IOS-XR support MD5 or SHA1 authentication
  A. The MSDP peers are also typically the RPs in respective routing domains.
  C. On Cisco IOS, IOS-XE, and IOS-XR, the router can be configured to cache the SA messages to reduce the join latency
  D. SA messages are used to advertise active sources in a domain
  E. MSDP establishes neighbor relationships with other MSDP peers using TCP port 639

  ---

  http://www.cisco.com/en/US/docs/ios/ipmulti/configuration/guide/imc_msdp_im_pim_sm.html When MSDP is enabled, an RP in a PIM-SM domain maintains MSDP peering relationships with MSDPenabled routers in other domains. This peering relationship occurs over a TCP connection, where primarily a list of sources sending to multicast groups is exchanged. MSDP uses TCP (port 639) for its peering connections. As with BGP, using point-to-point TCP peering means that each peer must be explicitly configured. The TCP connections between RPs, moreover, are achieved by the underlying routing system. The receiving RP uses the source lists to establish a source path. If the multicast sources are of interest to a domain that has receivers, multicast data is delivered over the normal, source-tree building mechanism provided by PIM- SM. MSDP is also used to announce sources sending to a group. These announcements must originate at the RP of the domain.