Cisco 642-885 Dumps PDF Study Guide

You need to pass this exam to get the CCNP Service Provider Certification. This 642-885 exam certification validates your skills to configure and optimize service provider IP next-generation network infrastructures.

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Question No. 1

Assume that the R1 router is enabled for PIM-SM and receives a multicast packet sourced from, and the R1 router has multicast receivers on the Gi0/1, Gi0/2, Gi0/3 and Gi0/4 interfaces.

The multicast packet from the source must arrive on which interface on the R1 router for it to be forwarded out the other interfaces?

Answer: A

Question No. 2

What is one of the configuration errors within an AS that can stop a Cisco IOS-XR router from announcing certain prefixes to its EBGP peers?

Answer: A

Question No. 3

Refer to the exhibit.

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

Answer: C

Question No. 4

Which multicast routing protocol is most optimal for supporting many-to-many multicast applications?

Answer: B

PIM-Bidirectional Operations

PIM Bidirectional (BIDIR) has one shared tree from sources to RP and from RP to receivers. This is unlike the PIM-SM, which is unidirectional by nature with multiple source trees – one per (S, G) or a shared tree from receiver to RP and multiple SG trees from RP to sources.

Benefits of PIM BIDIR are as follows:

* As many sources for the same group use one and only state (*, G), only minimal states are required in each router.

* No data triggered events.

* Rendezvous Point (RP) router not required. The RP address only needs to be a routable address and need not exist on a physical device.

Question No. 5

A network engineer for an ISP wants to reduce the number of iBGP adjacencies. A merge is taking place with another ISP network, so the network engineer needs to make both ASNs look like a single network for the Internet. Which BGP technology is most suitable?

Answer: B

Question No. 6

Refer to the exhibit.

Which statement correctly explains the bgp graceful-restart command?

Answer: B

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


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.

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