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Deploying Cisco Service Provider Advanced Network Routing

Question No: 11

Which two options are thecommon methods for implementing Site of Origin on Cisco IOS XE routers for loop avoidance in multihome BGP customers? (Choose two.)

1. Configure the route-map in command on the CE BGP neighbor.

2. Configure Site of Origin directly on the CE BGP neighbor command.

3. Configure site-map on VRF interface and redistribution of iBGP.

4. Configure site-map on VRF interface and network command.

5. Configure the route-map out command on the P router.

Answer: A,B

Question No: 12

Which two statements are correct regarding the multicast operations on the router that is the RP? (Choose two.)

1. It is using IGMPv3

2. The IGMP query interval is set to 125 seconds

3. It is using the IPv4 unicast routing table to perform the RPF checks

4. Static multicast routes are configured on the RP

Answer: A,C

Explanation: #show ip mroute

#show ip pim interface

#show ip igmp group

#show ip pim neighbor

Question No: 13

Refer to the exhibit.

Which statement correctly explains the bgp graceful-restart command?

1. This command is used to enable NSR and is entered on the NSR-capable router, and also on any NSR-aware peer

2. This command is used to enable NSF and is entered on the NSF-capable router, and also on any NSF-aware peer

3. This command is only required on the NSF-capable routers to enable BGP graceful restart with the BGP peers

4. This command is only required on the NSF-aware routers to enable BGP graceful restart with the BGP peers

5. This command is only required on the NSR-capable routers to enable BGP graceful restart with the BGP peers

Answer: B Explanation:

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 No: 14

When implementing interdomain multicast routing, which mechanism can be used to advertise multicast sources in one domain to the other domains, allowing the RPs to build interdomain multicast distribution trees?

1. Multiprotocol BGP

2. PIM

3. MSDP

4. Auto RP

5. BSR

6. MLD

Answer: C Explanation:

Multicast Source Discovery Protocol

Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM sparse-mode domains.

MSDP allows multicast sources for a group to be known to all rendezvous point(s) (RPs) in different domains.

Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains. An RP in a PIM-SM domain has MSDP peering relationships with MSDP-enabled routers in other domains.

Each peering relationship occurs over a TCP connection, which is maintained by the underlying routing system.

MSDP speakers exchange messages called Source Active (SA) messages. When an RP learns about a local active source, typically through a PIM register message, the MSDP process encapsulates the register in an SA message and forwards the information to its peers. The message contains the source and group information for the multicast flow, as well as any encapsulated data. If a neighboring RP has local joiners for the multicast group, the RP installs the S, G route, forwards the encapsulated data contained in the SA message, and sends PIM joins back towards the source. This process describes how a multicast path can be built between domains.

Question No: 15

Refer to the exhibit.

XR4 must protect itself from a DOS attack against its BGP process from R1 by using the

TTL security feature. Which configuration achieves this goal?

1. router bgp 100

   neighbor 10.10.14.1 ttl-security

2. router bgp 100

   neighbor 10.10.14.1 ttl-security hops 1

3. router bgp 100

   neighbor 10.10.14.1 ttl-security hops 254

4. router bgp 100

neighbor 10.10.14.1 ttl-security hops 255

Answer: A

Question No: 16

Which three statements are correct regarding the various multicast groups? (Choose three.)

1. Currently there is no source sending traffic to the 224.1.1.1 multicast group

2. PE5 has a Null OILforthe (*,224.0.1.40) entry

3. PE5 has a Null OILforthe (*,224.1.1.1) entry

4. CE5 has joined the 224.0.1.40 multicast group

5. CE5 has a Null OILforthe (*,224.1.1.1) entry

Answer: C,D,E

Explanation: #show ip mroute

Question No: 17

Which two statements regarding Auto RP operations and implementations are correct? (Choose two.)

1. Candidate RPs send RP announcements to the 224.0.1.39 multicast group, and the mapping agents send RP discovery messages to the 224.0.1.40 multicast group

2. Every PIM-SM router must be configured with the RP mapping agent IP address

3. Candidate RPs learn the IP address of the mapping agents via periodic RP discovery messages

4. Administrative scoping can be configured to limit the scope of the RP announcements

5. A Reverse Path Forwarding check is done on the RP discovery messages

6. RP discovery messages are flooded hop by hop throughout the network as multicast to the all PIM routers multicast group with a TTL of 1

Answer: A,D Explanation: Auto-RP

Automatic route processing (Auto-RP) is a feature that automates the distribution of group- to-RP mappings in a PIM network. This feature has these benefits:

It is easy to use multiple RPs within a network to serve different group ranges. It allows load splitting among different RPs.

It facilitates the arrangement of RPs according to the location of group participants.

It avoids inconsistent, manual RP configurations that might cause connectivity problems. Multiple RPs can be used to serve different group ranges or to serve as hot backups for each other. To ensure that Auto-RP functions, configure routers as candidate RPs so that they can announce their interest in operating as an RP for certain group ranges.

Additionally, a router must be designated as an RP-mapping agent that receives the RP- announcement messages from the candidate RPs, and arbitrates conflicts. The RPmapping agent sends the consistent group-to-RP mappings to all remaining routers. Thus, all routers automatically determine which RP to use for the groups they support auto- rp candidate-rp

To configure a router as a Protocol Independent Multicast (PIM) rendezvous point (RP) candidate that sends messages to the well-known CISCO-RP-ANNOUNCE multicast group (224.0.1.39), use the auto-rp candidaterp command in PIM configuration mode. To return to the default behavior, use the no form of this command. auto-rp candidate-rp type interface-path-id scope ttl-value [ group-list access-listname ] [ interval seconds ] [bidir] no auto-rp candidate-rp type interface-path-id scope ttl-value [ group-list access-listname] [ interval seconds ] [bidir]

Question No: 18

Which two options are characteristics ofconfiguration templates used by Cisco IOS XRto optimize BGP peering implementations? (Choose two.)

1. Session groups are used to inherit address family-specific configurations.

2. Cisco IOS XR provides by default a session group operating with all the supported address families.

3. Session groups are used to inherit address family-independent configurations.

4. Session groups can be included within a neighbor group.

5. Session groups can include neighbor groups.

Answer: C,D

Question No: 19

Which two statements regarding the BGP peerlngs are correct? (Choose two)

1. On PE5,the incoming prefixes received from the 192.168.105.51 EBGP peer is limited to a maximum of 10 prefixes

2. On PE5, the quot;rplinquot; inbound route policy is applied to the 192.168.105.51 EBGP peer

3. On PE5, the quot;passquot; outbound route policy is applied to the 192.168.105.51 EBGP peer

4. PE5 has one EBGP peer (CE5) and two IBGP peers (P1 and PE6)

5. PE5 has received a total of 60 prefixes from its neighbors

Answer: A,E

Explanation: #show ip bgp

Question No: 20

Which two BGP mechanisms are used to prevent routing loops when using a design with redundant route reflectors? (Choose two.)

1. Cluster-list

2. AS-Path

3. Originator ID

4. Community

5. Origin

Answer: A,C Explanation:

http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.7/routing/configuration/guide/rc37bgp

.html

As the iBGP learned routes are reflected, routing information may loop. The route reflector model has the following mechanisms to avoid routing loops:

鈥riginator ID is an optional, nontransitive BGP attribute. It is a 4-byte attributed created by a route reflector.

The attribute carries the router ID of the originator of the route in the local autonomous system. Therefore, if a misconfiguration causes routing information to come back to the originator, the information is ignored.

鈥luster-list is an optional, nontransitive BGP attribute. It is a sequence of cluster IDs that the route has passed. When a route reflector reflects a route from its clients to nonclient peers, and vice versa, it appends the local cluster ID to the cluster-list. If the cluster-list is empty, a new cluster-list is created. Using this attribute, a route reflector can identify if routing information is looped back to the same cluster due to misconfiguration. If the local cluster ID is found in the cluster-list, the advertisement is ignored.

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