Download New Updated (July) Cisco 400-101 Actual Test 131-140

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QUESTION 131

In which type of EIGRP configuration is EIGRP IPv6 VRF-Lite available?

 

A.

stub

B.

named mode

C.

classic mode

D.

passive

 

Correct Answer: B

Explanation:

The EIGRP IPv6 VRF Lite feature provides EIGRP IPv6 support for multiple VRFs. EIGRP for IPv6 can operate in the context of a VRF. The EIGRP IPv6 VRF Lite feature provides separation between routing and forwarding, providing an additional level of security because no communication between devices belonging to different VRFs is allowed unless it is explicitly configured. The EIGRP IPv6 VRF Lite feature simplifies the management and troubleshooting of traffic belonging to a specific VRF.

The EIGRP IPv6 VRF Lite feature is available only in EIGRP named configurations.

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6/configuration/15-2mt/ipv6-15-2mt-book/ip6-eigrp.html#GUID-92B4FF4F-2B68-41B0-93C8-AAA4F0EC1B1B

 

 

QUESTION 132

Two routers are trying to establish an OSPFv3 adjacency over an Ethernet link, but the adjacency is not forming. Which two options are possible reasons that prevent OSPFv3 to form between these two routers? (Choose two.)

 

A.

mismatch of subnet masks

B.

mismatch of network types

C.

mismatch of authentication types

D.

mismatch of instance IDs

E.

mismatch of area types

 

Correct Answer: DE

Explanation:

An OSPFv3 interface must have a compatible configuration with a remote interface before the two can be considered neighbors. The two OSPFv3 interfaces must match the following criteria:

 

clip_image002Hello interval

clip_image002[1]Dead interval

clip_image002[2]Area ID

clip_image002[3]Optional capabilities

 

The OSPFv3 header includes an instance ID field to identify that OSPFv3 packet for a particular OSPFv3 instance. You can assign the OSPFv3 instance. The interface drops all OSPFv3 packets that do not have a matching OSPFv3 instance ID in the packet header.

 

Reference: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_cli_nxos/l3_ospfv3.html

 

 

QUESTION 133

Like OSPFv2, OSPFv3 supports virtual links. Which two statements are true about the IPv6 address of a virtual neighbor? (Choose two.)

 

A.

It is the link-local address, and it is discovered by examining the hello packets received from the virtual neighbor.

B.

It is the link-local address, and it is discovered by examining link LSA received by the virtual neighbor.

C.

It is the global scope address, and it is discovered by examining the router LSAs received by the virtual neighbor.

D.

Only prefixes with the LA-bit not set can be used as a virtual neighbor address.

E.

It is the global scope address, and it is discovered by examining the intra-area-prefix-LSAs received by the virtual neighbor.

F.

Only prefixes with the LA-bit set can be used as a virtual neighbor address.

 

Correct Answer: EF

Explanation:

OSPF for IPv6 assumes that each router has been assigned link-local unicast addresses on each of the router’s attached physical links. On all OSPF interfaces except virtual links, OSPF packets are sent using the interface’s associated link-local unicast address as the source address. A router learns the link-local addresses of all other routers attached to its links and uses these addresses as next-hop information during packet forwarding.

On virtual links, a global scope IPv6 address MUST be used as the source address for OSPF protocol packets.

The collection of intra-area-prefix-LSAs originated by the virtual neighbor is examined, with the virtual neighbor’s IP address being set to the first prefix encountered with the LA-bit set.

Reference: https://tools.ietf.org/html/rfc5340

 

 

QUESTION 134

Which field is specific to the OPSFv3 packet header, as opposed to the OSPFv2 packet header?

 

A.

checksum

B.

router ID

C.

AuType

D.

instance ID

 

Correct Answer: D

Explanation:

In OSPFv3, Instance ID is a new field that is used to have multiple OSPF process’ instance per link. By default it is 0 and for any additional instance it is increased, instance ID has local link significance only. OSPFv3 routers will only become neighbors if the instanceIDs match. It is thus possible to have multiple routers on a broadcast domain and all run Ospfv3 but not all of them becoming neighbors.

Reference: https://supportforums.cisco.com/document/97766/comparing-ospfv3-ospfv2-routing-protocol

 

 

QUESTION 135

Which two functions are performed by the DR in OSPF? (Choose two.)

 

A.

The DR originates the network LSA on behalf of the network.

B.

The DR is responsible for the flooding throughout one OSPF area.

C.

The DR forms adjacencies with all other OSPF routers on the network, in order to synchronize the LSDB across the adjacencies.

D.

The DR is responsible for originating the type 4 LSAs into one area.

 

Correct Answer: AC

Explanation:

The DR originates the network LSA (LSA Type 2) which lists all the routers on the segment it is adjacent to -> A is correct.

Types 2 are ooded within its area only; does not cross ABR -> B is incorrect.

The broadcast and non-broadcast network types elect a DR/BDR. They f
orm adjacencies to all other OSPF routers on the network and help synchronize the Link State Database (LSDB) across the adjacencies -> C is correct.

LSAs Type 4 are originated by the ABR to describe an ASBR to routers in other areas so that routers in other areas know how to get to external routes through that ASBR -> D is incorrect.

 

 

QUESTION 136

Refer to the exhibit. AS #1 and AS #2 have multiple EBGP connections with each other. AS #1 wants all return traffic that is destined to the prefix 10.10.10.1/32 to enter through the router R1 from AS #2. In order to achieve this routing policy, the AS 1 advertises a lower MED from R1, compared to a higher MED from R3, to their respective BGP neighbor for the prefix 10.10.10.0/24. Will this measure guarantee that the routing policy is always in effect?

 

clip_image004

 

A.

Yes, because MED plays a deterministic role in return traffic engineering in BGP.

B.

Yes, because a lower MED forces BGP best-path route selection in AS #2 to choose R1 as the best path for 10.10.10.0/24.

C.

Yes, because a lower MED in AS #2 is the highest BGP attribute in BGP best-path route selection.

D.

No, AS #2 can choose to alter the weight attribute in R2 for BGP neighbor R1, and this weight value is cascaded across AS #2 for BGP best-path route selection.

E.

No, AS #2 can choose to alter the local preference attribute to overwrite the best-path route selection over the lower MED advertisement from AS #1. This local preference attribute is cascaded across AS #2 for the BGP best-path route selection.

 

Correct Answer: E

Explanation:

MED and AS path prepending can both be used to influence the way incoming traffic from other Autonomous Systems get sent to the local AS, but they provide no guarantee as the other AS ultimately has the final word in how they send traffic. Since local preference is preferred over MED in the BGP decision process, the other AS can configure local preference to override the MED settings you have configured.

 

 

 

QUESTION 137

Refer to the exhibit. What does “(received-only)” mean?

 

clip_image006

 

A.

The prefix 10.1.1.1 can not be advertised to any eBGP neighbor.

B.

The prefix 10.1.1.1 can not be advertised to any iBGP neighbor.

C.

BGP soft reconfiguration outbound is applied.

D.

BGP soft reconfiguration inbound is applied.

 

Correct Answer: D

Explanation:

When you configure bgp soft-configuration-inbound, all the updates received from the neighbor will be stored unmodified, regardless of the inbound policy, and these routes appear as “(received-only).”

 

 

QUESTION 138

Which regular expression will only allow prefixes that originated from AS 65000 and that are learned through AS 65001?

 

A.

^65000_65001$

B.

65000_65001$

C.

^65000_65001

D.

^65001_65000$

 

Correct Answer: D

Explanation:

The following table lists the regular expressions and their meanings:

 

+——————————————————+

| CHAR | USAGE |

+——————————————————|

| ^ | Start of string |

|——|———————————————–|

| $ | End of string |

|——|———————————————–|

| [] | Range of characters |

|——|———————————————–|

| – | Used to specify range ( i.e. [0-9] ) |

|——|———————————————–|

| ( ) | Logical grouping |

|——|———————————————–|

| . | Any single character |

|——|———————————————–|

| * | Zero or more instances |

|——|———————————————–|

| + | One or more instance |

|——|———————————————–|

| ? | Zero or one instance |

|——|———————————————–|

| _ | Comma, open or close brace, open or close |

| | parentheses, start or end of string, or space |

+——————————————————+

Some commonly used regular expressions include:

+————-+—————————+

| Expression | Meaning |

|————-+—————————|

| .* | Anything |

|————-+—————————|

| ^$ | Locally originated routes |

|————-+—————————|

| ^100_ | Learned from AS 100 |

|————-+—————————|

| _100$ | Originated in AS 100 |

|————-+—————————|

| _100_ | Any instance of AS 100 |

|————-+—————————|

| ^[0-9]+$ | Directly connected ASes |

+———
—-+—————————+

 

Reference: http://blog.ine.com/2008/01/06/understanding-bgp-regular-expressions/

 

 

QUESTION 139

Which statement describes the BGP add-path feature?

 

A.

It allows for installing multiple IBGP and EBGP routes in the routing table.

B.

It allows a network engineer to override the selected BGP path with an additional path created in the config.

C.

It allows BGP to provide backup paths to the routing table for quicker convergence.

D.

It allows multiple paths for the same prefix to be advertised.

 

Correct Answer: D

Explanation:

BGP routers and route reflectors (RRs) propagate only their best path over their sessions. The advertisement of a prefix replaces the previous announ
cement 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.

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

 

 

QUESTION 140

Refer to the exhibit. What is a reason for the RIB-failure?

 

clip_image008

 

A.

CEF is not enabled on this router.

B.

The route 10.100.1.1/32 is in the routing table, but not as a BGP route.

C.

The routing table has yet to be updated with the BGP route.

D.

The BGP route is filtered inbound and hence is not installed in the routing table.

 

Correct Answer: B

Explanation:

A rib-failure occurs when BGP tries to install the bestpath prefix into the RIB, but the RIB rejects the BGP route because a route with better administrative distance already exists in the routing table. An inactive Border Gateway Protocol (BGP) route is a route that is not installed in the RIB, but is installed in the BGP table as rib-failure.

Example Topology

Router 1 (R1) and router 2 (R2) have two parallel links; one links runs BGP AS 65535 and the other link runs Enhanced Interior Gateway Routing Protocol (EIGRP) AS 1. Both BGP and EIGRP are advertising the network 10.1.1.1/32 on R1.

 

clip_image010

 

R2 learns about the 1.1.1.1/32 route through both EIGRP and BGP, but installs only the EIGRP route in the routing table because of the lower administrative distance. Since the BGP route is not installed in the R2 routing table, the route appears as a rib-failure in the R2 BGP table.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/116146-config-bgp-next-hop-00.html

 

 

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