These skills prove fruitful to accomplish the real exam objectives. Skills to configure and optimize service provider IP next-generation network infrastructures are essential to pass the CCNP Service Provider Certification of 642-885 exam.

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Question No. 1

Refer to the Cisco IOS-XR show output exhibit.

Which two statements are correct? (Choose two.)

Answer: A, D

Question No. 2

Instructions

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

Answer: C, D, E

#show ip mroute

Question No. 3

What is enabled by default on Cisco IOS-XR routers and cannot be disabled?

Answer: C

Before using the BGP policy accounting feature, you must enable BGP on the router (CEF is enabled by default).

Question No. 4

Given the IPv6 address of 2001:0DB8::1:800:200E:88AA, what will be its corresponding the solicited-node multicast address?

Answer: D

IPv6 nodes (hosts and routers) are required to join (receive packets destined for) the following multicast groups:

*All-nodes multicast group FF02:0:0:0:0:0:0:1 (scope is link-local)

*Solicited-node multicast group FF02:0:0:0:0:1:FF00:0000/104 for each of its assigned unicast and anycast addresses

IPv6 routers must also join the all-routers multicast group FF02:0:0:0:0:0:0:2 (scope is link-local).

The solicited-node multicast address is a multicast group that corresponds to an IPv6 unicast or anycast address. IPv6 nodes must join the associated solicited-node multicast group for every unicast and anycast address to which it is assigned. The IPv6 solicited-node multicast address has the prefix FF02:0:0:0:0:1:

FF00:0000/104 concatenated with the 24 low-order bits of a corresponding IPv6 unicast or anycast address (see Figure 2). For example, the solicited-node multicast address corresponding to the IPv6 address 2037::01:800:200E:8C6C is FF02::1:FF0E:8C6C. Solicited-node addresses are used in neighbor solicitation messages

Question No. 5

Refer to the topology diagram shown in the exhibit and the partial configurations shown below.

Once the attack from 209.165.201.144/28 to 209.165.202.128/28 has been detected, which additional configurations are required on the P1 IOS-XR router to implement source-based remote-triggered black hole filtering?

!

router bgp 123

address-family ipv4 unicast

redistribute static route-policy test

!

Answer: C

Source-Based RTBH Filtering

With destination-based black holing, all traffic to a specific destination is dropped after the black hole has been activated, regardless of where it is coming from. Obviously, this could include legitimate traffic destined for the target. Source-based black holes provide the ability to drop traffic at the network edge based on a specific source address or range of source addresses.

If the source address (or range of addresses) of the attack can be identified (spoofed or not), it would be better to drop all traffic at the edge based on the source address, regardless of the destination address. This would permit legitimate traffic from other sources to reach the target. Implementation of source-based black hole filtering depends on Unicast Reverse Path Forwarding (uRPF), most often loose mode uRPF. Loose mode uRPF checks the packet and forwards it if there is a route entry for the source IP of the incoming packet in the router forwarding information base (FIB). If the router does not have an FIB entry for the source

IP address, or if the entry points to a null interface, the Reverse Path Forwarding (RPF) check fails and the packet is dropped, as shown in Figure 2. Because uRPF validates a source IP address against its FIB entry, dropping traffic from specific source addresses is accomplished by configuring loose mode uRPF on the external interface and ensuring the RPF check fails by inserting a route to the source with a next hop of Null0. This can be done by using a trigger device to send IBGP updates. These updates set the next hop for the source IP to an unused IP address that has a static entry at the edge, setting it to null as shown in Figure 2.

Question No. 6

The following Cisco IOS-XR configuration command will globally enable which multicast process(es) on the router?

RP/0/RP0/CPU0:router(config)# multicast-routing

Answer: E

http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.5/multicast/configuration/guide/mc35mcst.html

Multicast-routing Configuration Submode

When you issue the multicast-routing ipv4 or multicast-routing ipv6 command, all default multicast components (PIM, IGMP, MLD, MFWD, and MRIB) are automatically started, and the CLI prompt changes to “config-mcastipv4” or “config-mcast-ipv6”, indicating that you have entered multicast-routing configuration submode

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