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CCIE Routing and Switching Written Exam v5.1

QUESTION 511

Which two options are ways in which an OSPFv3 router handles hello packets with a clear address-family bit? (Choose two.)

 

A.

IPv4 unicast packets are discarded.

B.

IPv6 unicast packets are discarded.

C.

IPv4 unicast packets are forwarded.

D.

IPv6 unicast packets are forwarded.

 

Correct Answer: AD

Explanation:

A typical distance vector protocol saves the following information when computing the best path to a destination: the distance (total metric or distance, such as hop count) and the vector (the next hop). For instance, all the routers in the network in Figure 1 are running Routing Information Protocol (RIP). Router Two chooses the pa
th to Network A by examining the hop count through each available path.

 

clip_image002

 

Since the path through Router Three is three hops, and the path through Router One is two hops, Router Two chooses the path through One and discards the information it learned through Three.

If the path between Router One and Network A goes down, Router Two loses all connectivity with this destination until it times out the route of its routing table (three update periods, or 90 seconds), and Router Three re-advertises the route (which occurs every 30 seconds in RIP). Not including any hold-down time, it will take between 90 and 120 seconds for Router Two to switch the path from Router One to Router Three.

EIGRP, instead of counting on full periodic updates to re-converge, builds a topology table from each of its neighbor’s advertisements (rather than discarding the data), and converges by either looking for a likely loop-free route in the topology table, or, if it knows of no other route, by querying its neighbors. Router Two saves the information it received from both Routers One and Three. It chooses the path through One as its best path (the successor) and the path through Three as a loop-free path (a feasible successor). When the path through Router One becomes unavailable, Router Two examines its topology table and, finding a feasible successor, begins using the path through Three immediately.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routingprotocol-eigrp/16406-eigrp-toc.html

 

 

QUESTION 512

Which three statements about VTP version 3 are true? (Choose three.)

 

A.

It supports other databases in addition to VLAN.

B.

It supports VLANs up to 4095.

C.

It supports the synchronization of switch configuration templates between switches in the domain.

D.

It supports the transfer of information about private VLAN structures.

E.

It supports the transfer of PVST+ configuration information.

F.

It supports RSTP.

 

Correct Answer: ABD

Explanation:

Much work has gone into improving the usability of VTP version 3 in three major areas:

clip_image004The new version of VTP offers better administrative control over which device is allowed to update other devices’ view of the VLAN topology. The chance of unintended and disruptive changes is significantly reduced, and availability is increased. The reduced risk of unintended changes will ease the change process and help speed deployment.

clip_image005Functionality for the VLAN environment has been significantly expanded. Two enhancements are most beneficial for today’s networks:

In addition to supporting the earlier ISL VLAN range from 1 to 1001, the new version supports the whole IEEE 802.1Q VLAN range up to 4095.

In addition to supporting the concept of normal VLANs, VTP version 3 can transfer information regarding Private VLAN (PVLAN) structures.

clip_image004[1]The third area of major improvement is support for databases other than VLAN (for example, MST).

Reference: http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-6500-seriesswitches/solution_guide_c78_508010.html

 

 

QUESTION 513

Refer to the exhibit. If the downstream router has a summary route configured, which two actions must you take on the local router to create the summary route that summarizes all routes from the downstream router? (Choose two.)

 

clip_image006

 

A.

Configure the summary address on the interface.

B.

Use 10.0.0.0 255.248.0.0 as the summary route.

C.

Configure the summary address in the EIGRP process.

D.

Use 10.0.0.0 255.252.0.0 as the summary route.

E.

Configure a route map to permit the route.

F.

Configure a distribute list in.

 

Correct Answer: AB

Explanation:

Route summarization works in conjunction with the ip summary-address eigrp interface configuration command, in which additional summarization can be performed To correctly summarize all the networks shown, the correct route to use is 10.0.0.0 255.248.0.0.

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfeigrp.html

 

 

 

 

 

QUESTION 514

Refer to the exhibit. R2 is configured as the R1 neighbor in area 51, but R2 fails to receive the configured summary route. Which action can you take to correct the problem?

 

clip_image007

 

A.

Replace the summary-address command with the area-range command.

B.

Configure a summary address under R1interface GigabitEthernet0/0.

C.

Configure a summary address under R1 interface GigabitEthernet1/0.

D.

Configure the no discard-route command in the OSPF process of R1.

E.

Configure ip ospf network broadcast under the Loopback0 interface of R1.

 

Correct Answer: A

 

 

QUESTION 515

Which BGP feature allows a router to maintain its current BGP configuration while it advertises a different AS number to new connections?

 

A.

local-AS

B.

next-hop-self

C.

allow-AS in

D.

soft reset

 

Correct Answer: A

Explanation:

The local-AS feature allows a router to appear to be a member of a second autonomous system (AS), in addition to its real AS. This feature can only be used for true eBGP peers.

The local-AS feature is useful if ISP-A purchases ISP-B, but ISP-B’s customers do not want to modify any peering arrangements or configurations. The local-AS feature allows routers in ISP-B to become members of ISP-A’s AS. At the same time, these routers appear to their customers to retain their ISP-B AS number.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13761-39.html

 

 

 

 

 

QUESTION 516

For which two conditions is Cisco Express Forwarding recursion disabled by default when the BGP Prefix Independent Convergence functionality is enabled? (Choose two.)

 

A.

next hops learned with a /24 mask

B.

next hops learned with any mask shorter than /32

C.

next hops learned with a /32 mask

D.

next hops that are directly connected

 

Correct Answer: CD

Explanation:

Recursion is the ability to find the next longest matching path when the primary path goes down. When the BGP PIC feature is not installed, and if the next hop to a prefix fails, Cisco Express Forwarding finds the next path to reach the prefix by recursing through the FIB to find the next longest matching path to the prefix. This is useful if the next hop is multiple hops away and there is more than one way of reaching the next hop.

However, with the BGP PIC feature, you may want to disable Cisco Express Forwarding recursion for the following reasons:

Recursion slows down convergence when Cisco Express Forwarding searches all the FIB entries.

BGP PIC Edge already precomputes an alternate path, thus eliminating the need for Cisco Express Forwarding recursion.

When the BGP PIC functionality is enabled, Cisco Express Forwarding recursion is disabled by default for two conditions:

For next hops learned with a /32 network mask (host routes)

For next hops that are directly connected

For all other cases, Cisco Express Forwarding recursion is enabled.

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3s-book/irg-bgp-mp-pic.html

 

 

QUESTION 517

Refer to the exhibit. This network is configured with PIM, and the RPF check has failed toward the multicast source. Which two configuration changes must you make to router R3 to enable the RPF check to pass? (Choose two.)

 

clip_image009

 

A.

Configure a static multicast route to the multicast source through the tunnel interface.

B.

Configure a static multicast route to the multicast source LAN through the tunnel interface.

C.

Configure a static multicast route to the multicast source LAN through the Ethernet interface.

D.

Remove the command ip prim bidir-enable from the R3 configuration.

 

Correct Answer: AB

 

 

QUESTION 518

You are configuring a DMVPN hub to perform CBWFQ on a per-spoke basis. Which information is used to identify the spoke?

 

A.

the NHRP network ID

B.

the spoke tunnel source IP

C.

the spoke tunnel interface IP address

D.

the NHRP group

 

Correct Answer: D

 

 

QUESTION 519

Which two features improve BGP convergence? (Choose two.)

 

A.

Next-hop address tracking

B.

Additional paths

C.

Advertise map

D.

Communities

E.

Soft reconfiguration

 

Correct Answer: AB

Explanation:

The BGP Support for Next-Hop Address Tracking feature is enabled by default when a supporting Cisco software image is installed. BGP next-hop address tracking is event driven. BGP prefixes are automatically tracked as peering sessions are established. Next-hop changes are rapidly reported to the BGP routing process as they are updated in the RIB. This optimization improves overall BGP convergence by reducing the response time to next-hop changes for routes installed in the RIB. When a best path calculation is run in between BGP scanner cycles, only next-hop

changes are tracked and processed.

BGP routers and route reflectors (RRs) propagate only their best path over their sessions. The advertisement of a prefix replaces the previous announcement of that prefix (this behavior is known as an implicit withdraw). The implicit withdraw can achieve better scaling, but at the cost of path diversity.

Path hiding can prevent efficient use of BGP multipath, prevent hitless planned maintenance, and can lead to MED oscillations and suboptimal hot-potato routing. Upon nexthop failures, path hiding also inhibits fast and local recovery because the network has to wait for BGP control plane convergence to restore traffic. The BGP Additional Paths feature provides a generic way of offering path diversity; the Best External or Best Internal features offer path diversity only in limited scenarios.

The BGP Additional Paths feature provides a way for multiple paths for the same prefix to be advertised without the new paths implicitly replacing the previous paths. Thus, path diversity is achieved instead of path hiding.

References:

http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_bgp/configuration/15-1sg/irgnexthop-track.html

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3sbook/bgp_additional_paths.html

QUESTION 520

Refer to the exhibit. Which statement is true about why the first-hop PIM IPv6 router is stuck in registering?

 

clip_image010

 

A.

The scope of the IPv6 multicast address is link-local.

B.

The outgoing interface for the IPv6 multicast group should not be a tunnel interface.

C.

The R-bit is set in the IPv6 address, but this is not an embedded RP multicast IPv6 address.

D.

The S flag should not be set on a first-hop PIM router.

E.

A multicast IPv6 address does not start with FF.

 

Correct Answer: C

Explanation:

R bit: RP bit: R = 1 indicates the address embeds the address of the Rendezvous Point (RP). The embedded RP address needs to begin with the prefix FF70::/12, But here we see that the address is FF7E::1234.

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