642-885 Latest Exam (Mar 2018)

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Deploying Cisco Service Provider Advanced Network Routing

Question No: 71

Which of the following can be used by dual-stack service providers supporting IPv4/IPv6 customers with dual-stack hosts using public IPv6 addresses and private IPv4 addresses?

  1. NAT64

  2. 6RD

  3. 6to4 tunnels

  4. Carrier-grade NAT

Answer: D Explanation:

Carrier Grade NAT is a large-scale NAT, capable of providing private-IPv4-to-public-IPv4 translation in the order of millions of translations. Carrier Grade NAT can support several hundred thousand subscribers with the bandwidth throughput of at least 10Gb/s full-duplex. With IPv4 addresses reaching depletion, Carrier Grade NAT is vital in providing private IPv4 connectivity to the public IPv4 internet. In addition, Carrier Grade NAT is not limited to IPv4 NAT; it can also translate between IPv4 and IPv6 addresses.

Question No: 72

Which multicast routing protocol supports dense mode, sparse mode and bidirectional mode?

  1. DVMRP

  2. MOSPF

  3. PIM

  4. MP-BGP

  5. MSDP

Answer: C

Question No: 73

An SP core is running PIM on the network. Multicast groups in this networkare in the range. Which commandenables multicast routing operations without using an RP?

  1. ip pim autorp

  2. ip pim ssm default

  3. ip pim bidir-enable

  4. ip pim register-source

Answer: B

Question No: 74

With PIM-SM operations, which four pieces of information are maintained in the multicast routing table for each (*,G) or (S,G) entry? (Choose four.)

  1. RPF Neighbor

  2. RP Set

  3. Incoming Interface

  4. OIL

  5. DF priority

  6. PIM SM state flags

Answer: A,C,D,F Explanation:

The following is sample output from the show ip mroute command for a router operating in sparse mode:

show ip mroute

IP Multicast Routing Table

Flags: D – Dense, S – Sparse, C – Connected, L – Local, P – Pruned R – RP-bit set, F – Register flag, T – SPT-bit set

Timers: Uptime/Expires

Interface state: Interface, Next-Hop, State/Mode

(*,, uptime 5:29:15, RP is, flags: SC

Incoming interface: Tunnel0, RPF neighbor, Dvmrp Outgoing interface list:

Ethernet0, Forward/Sparse, 5:29:15/0:02:57

(,, uptime 5:29:15, expires 0:02:59, flags: C

Incoming interface: Tunnel0, RPF neighbor Outgoing interface list:

Ethernet0, Forward/Sparse, 5:29:15/0:02:57

Question No: 75

When enabling interdomain multicast routing, which two statements are correct? (Choose two.)

  1. Multiprotocol BGP is used instead of PIM SM to build the intradomain and interdomain multicast distribution trees

  2. Use MSDP to enable the RPs from different domains to exchange information about active multicast sources

  3. MSDP SA packets are sent between the multiprotocol BGP peers

  4. Noncongruent unicast and multicast topologies can be supported using multiprotocol BGP

Answer: B,D Explanation:


MSDP In the PIM-SM model, multicast sources and receivers must register with their local RP. Actually, the router closest to the sources or receivers registers with the RP, but the key point to note is that the RP knows about all the sources and receivers for any particular group. RPs in other domains have no way of knowing about sources located in other domains. MSDP is an elegant way to solve this problem.

MSDP is a mechanism that allows RPs to share information about active sources. RPs know about the receivers in their local domain. When RPs in remote domains hear about the active sources, they can pass on that information to their local receivers and multicast

data can then be forwarded between the domains. A useful feature of MSDP is that it allows each domain to maintain an independent RP that does not rely on other domains, but it does enable RPs to forward traffic between domains. PIM-SM is used to forward the traffic between the multicast domains.

The RP in each domain establishes an MSDP peering session using a TCP connection with the RPs in other domains or with border routers leading to the other domains. When the RP learns about a new multicast source within its own domain (through the normal PIM register mechanism), the RP encapsulates the first data packet in a Source-Active (SA) message and sends the SA to all MSDP peers. The SA is forwarded by each receiving peer using a modified RPF check, until the SA reaches every MSDP router in the interconnected networks-theoretically the entire multicast internet. If the receiving MSDP peer is an RP, and the RP has a (*, G) entry for the group in the SA (there is an interested receiver), the RP creates (S, G) state for the source and joins to the shortest path tree for the source. The encapsulated data is decapsulated and forwarded down the shared tree of that RP. When the packet is received by the last hop router of the receiver, the last hop router also may join the shortest path tree to the source. The MSDP speaker periodically sends SAs that include all sources within the own domain of the RP



Multiprotocol BGP

Multiprotocol BGP is an enhanced BGP that carries routing information for multiple network layer protocols and IP multicast routes. BGP carries two sets of routes, one set for unicast routing and one set for multicast routing.

The routes associated with multicast routing are used by the Protocol Independent Multicast (PIM) feature to build data distribution trees.

Multiprotocol BGP is useful when you want a link dedicated to multicast traffic, perhaps to limit which resources are used for which traffic. Multiprotocol BGP allows you to have a unicast routing topology different from a multicast routing topology providing more control over your network and resources.

In BGP, the only way to perform interdomain multicast routing was to use the BGP infrastructure that was in place for unicast routing. Perhaps you want all multicast traffic exchanged at one network access point (NAP).

If those routers were not multicast capable, or there were differing policies for which you wanted multicast traffic to flow, multicast routing could not be supported without multiprotocol BGP.

Note It is possible to configure BGP peers that exchange both unicast and multicast

network layer reachability information (NLRI), but you cannot connect multiprotocol BGP clouds with a BGP cloud. That is, you cannot redistribute multiprotocol BGP routes into BGP.

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Question No: 76

A junior network engineer has just configured a new IBGP peering between two Cisco ASR9K PE routers in the network using the loopback interface of the router, but the IBGP neighborship is not able to be established. Which two verification steps will be helpful in troubleshooting this problem? (Choose two.)

  1. Verify that the network command under router BGP is configured correct on each router for announcing the router#39;s loopback interface in BGP

  2. Verify that the ibgp-multihop command under the BGP neighbor is configured correctly on each router

  3. Verify that the loopback interfaces are reachable over the IGP

  4. Verify that the update-source loopback command under the BGP neighbor is configured correctly on each router

  5. Verify that the ttl-security command under the BGP neighbor is configured correctly on each router to enable the router to send the BGP packets using a proper TTL value

  6. Verify that the UDP port 179 traffic is not being blocked by an ACL or firewall between the two IBGP peers

Answer: C,D

Question No: 77

Which three methods can be used to reduce the full-mesh IBGP requirement in a service provider core network? (Choose three.)

  1. Implement route reflectors

  2. Enable multi-protocol BGP sessions between all the PE routers

  3. Implement confederations

  4. Implement MPLS (LDP) in the core network on all the PE and P routers

  5. Enable BGP synchronization

  6. Disable the IBGP split-horizon rule

Answer: A,C,D

Question No: 78

Which of the following is a feature added in IGMPv3?

  1. Support for source filtering

  2. Support for Host Membership Report and a Leave Group message

  3. Uses a new variation of the Host Membership Query called the Group-Specific Host Membership Query

  4. Uses an election process to determine the querying router on the LAN

  5. Uses an election process to determine the designated router on the LAN

  6. IPv6 support

Answer: A

Question No: 79

Refer to the Cisco IOS-XR BGP configuration exhibit.

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Identify two configuration errors. (Choose two.)

  1. The neighbor-group efg is missing the ebgp-multihop 2 configuration

  2. The ttl-security configuration command is missing the option to set the number of hops

  3. The passall route policy is wrong

  4. The route-policy passall in and route-policy passall out commands should be configured under the neighbor-group efg instead of the af-group abc

  5. The maximum-prefix 10 configuration should be configured under the af-group abc instead of the neighbor-group efg

Answer: C,E Explanation:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801 0a28a.shtml

Question No: 80

Refer to the Cisco IOS-XR configuration exhibit.

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The Cisco IOS-XR router is unable to establish any PIM neighbor relationships. What is wrong with the configuration?

  1. The configuration is missing:

    interface gi0/0/0/0 ip pim sparse-mode interface gi0/0/0/1 ip pim sparse-mode interface loopback0 ip pim sparse-mode

  2. The configuration is missing: multicast-routing

    address-family ipv4 interface gi0/0/0/0 enable

    interface gi0/0/0/1 enable

  3. The auto-rp scoping configurations should be set to 1 not 16

  4. The RP address has not been configured using the rp-address router PIM configuration command

  5. PIM defaults to dense mode operations only, so PIM sparse mode must be enabled using the pim sparse-mode router PIM configuration command

Answer: B

equipment router to allow an ISP to automate the process of assigning a block of IPv6 addresses to a customer for use within the customer network?

  1. Router Advertisement

  2. DHCPv6 Prefix Delegation

  3. DHCPv6 Lite

  4. Stateful DHCPv6

Answer: B Explanation:

http://www.cisco.com/en/US/tech/tk872/technologies_configuration_example09186a0080b 8a116.shtml

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