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Cisco 642-885 Dumps

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Cisco
Deploying Cisco Service Provider Advanced Routing (SPADVROUTE)
Cisco
Deploying Cisco Service Provider Advanced Routing (SPADVROUTE)

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Questions & Answers for Cisco 642-885

Showing 1-15 of 131 Questions

Question #1

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?

A. Some prefixes were mistagged with the no-export BGP community

B. Some prefixes were set with an MED of 0

C. The outbound BGP route policy only has set actions defined without any pass actions defined

D. The inbound BGP route policy only has set actions defined without any pass actions defined

Question #2





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

A. It is using IGMPv3

B. The IGMP query interval is set to 125 seconds

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

D. Static multicast routes are configured on the RP

Explanation: #show ip mroute
#show ip pim interface
#show ip igmp group
#show ip pim neighbor

Question #3

Which four operations are components of MSDP in interdomain multicast setup? (Choose
four.)

A. Multiple domains can have a single statically defined RP.

B. RPs interconnect between domains with UDP connections to pass source active messages.

C. RPs interconnect between domains with TCP connections to pass source active messages.

D. RPs send source active messages for internal sources to MSDP peers.

E. Source active messages are Peer-RPF checked before accepting or forwarding.

F. RPs learn about external sources via source active messages and may trigger (S,G) joins on behalf of local receivers.

G. MSDP connections typically parallel PIM-SM connections.

Question #4

Which of the following is a feature added in IGMPv3?

A. Support for source filtering

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

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

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

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

F. IPv6 support

Question #5

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?

A. router bgp 100 neighbor 10.10.14.1 ttl-security

B. router bgp 100 neighbor 10.10.14.1 ttl-security hops 1

C. router bgp 100 neighbor 10.10.14.1 ttl-security hops 254

D. router bgp 100 neighbor 10.10.14.1 ttl-security hops 255

Question #6

Which two functions are supported for BGP extension MP-BGP for IP multicasting?
(Choose two.)

A. A network can support incongruent unicast and multicast topologies.

B. A network can support congruent unicast and multicast topologies.

C. MP-BGP is an enhanced BGP that carries routing information for multiple network layer protocols and IP multicast routes.

D. MP-BGP carries single sets of routes for unicast routing and multicast routing.

E. MP-BGP is useful when a link dedicated to multicast and unicast traffic is desired.

Question #7

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

Explanation:
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 #8

When implementing source-based remote-triggered black hole filtering, which two
configurations are required on the edge routers that are not the signaling router? (Choose
two.)

A. A static route to a prefix that is not used in the network with a next hop set to the Null0 interface

B. A static route pointing to the IP address of the attacker

C. uRPF on all external facing interfaces at the edge routers

D. Redistribution into BGP of the static route that points to the IP address of the attacker

E. A route policy to set the redistributed static routes with the no-export BGP community

Explanation:
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 #9

Refer to the exhibit.

Which option is the function of designing a hub and spoke confederation?

A. allows transit backbone area 66000 to be a blackhole for non-transit ASs

B. reduces the iBGP mesh, iBGP mesh will be in sub non-transit ASs

C. increases eBGP sessions between the confederation sub ASs

D. allows transit backbone area and non-transit ASs to run the same IGP

Question #10

After configuring the tunnel interface as shown in the exhibit, no IPv6 traffic is passed over
the IPv4 network.

Which additional configuration is required to pass the IPv6 traffic over the IPv4 network?

A. Configure an IPv4 address on the tunnel0 interface

B. Configure an IPv6 static route to send the required IPv6 traffic over the tunnel0 interface

C. The tunnel destination should be pointing to an IPv6 address instead of an IPv4 address

D. The tunnel0 interface IPv6 address must use the 2002:://16 prefix

Question #12

Refer to the exhibit. R2cannot to learn RP information from XR3. Which issue is the source
of the problem?

A. XR3 is not the DR.

B. Multicast routing is not enabled on the XR3 Giga0/0/0/0 interface.

C. R2 is learning the RP address via non-IGP routing protocol.

D. Multicast routing is not enabled on the XR3 Loopback0 interface.

E. BGP IPv4 MDT address family is not enabled on XR3.

Question #13

Which difference occurs between intradomain and interdomain routing technology?

A. PIM is used in intradomain routing technology and uses reverse path forwarding mechanism to implement optimize multicast data forwarding.

B. MSDP is used in intradomain routing technology to discover the multicast source.

C. Interdomain routing technology uses MSDP and M-BGP for exchanging multicast routing information.

D. RP is not needed in intradomain routing technology, but RP is needed in interdomain routing technology to receive multicast traffic.

Question #14

Which multicast group range is reserved for SSM?

A. 224.0.0.0/8

B. 225.0.0.0/8

C. 232.0.0.0/8

D. 239.0.0.0/8

Explanation:
PIM-SSM Operations
PIM in Source Specific Multicast operation uses information found on source addresses for
a multicast group provided by receivers and performs source filtering on traffic.
By default, PIM-SSM operates in the 232.0.0.0/8 multicast group range for IPv4 and
ff3x::/32 (where x is any valid scope) in IPv6. To configure these values, use the ssm range
command.
If SSM is deployed in a network already configured for PIM-SM, only the last-hop routers
must be upgraded with Cisco IOS XR software that supports the SSM feature.
No MSDP SA messages within the SSM range are accepted, generated, or forwarded

Question #15

Refer to the exhibit.

Which configuration is missing to complete the configuration task of enabling BFD with the
192.168.1.1 EBGP peer?

A. bfd fast-detect also needs to be enabled globally under router bgp 64500 RP/0/RSP0/CPU0:P1(config-bgp)#bfd fast-detect

B. bfd fast-detect also needs to be enabled for the address-family under address-family ipv4 unicast RP/0/RSP0/CPU0:P1(config-bgp-af)#bfd fast-detect

C. bfd fast-detect also needs to be enabled for the 192.168.1.1 neighbor under neighbor 192.168.1.1 RP/0/RSP0/CPU0:P1(config-bgp-nbr)#bfd fast-detect

D. bfd fast-detect also needs to be enabled for the 192.168.1.1 neighbor address-family under neighbor 192.168.1.1 address-family ipv4 unicast RP/0/RSP0/CPU0:P1(config-bgp-nbr-af)#bfd fast-detect

E. bfd fast-detect also needs to be enabled globally on the router RP/0/RSP0/CPU0:P1(config)#bfd fast-detect

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