Download New Updated (July) Cisco 400-101 Actual Test 201-210

Ensurepass

 

QUESTION 201

Which two statements are true about IS-IS? (Choose two.)

 

A.

IS-IS DIS election is nondeterministic.

B.

IS-IS SPF calculation is performed in three phases.

C.

IS-IS works over the data link layer, which does not provide for fragmentation and reassembly.

D.

IS-IS can never be routed beyond the immediate next hop.

 

Correct Answer: CD

Explanation:

IS-IS runs directly over the data link alongside IP. On Ethernet, IS-IS packets are always 802.3 frames, with LSAPs 0xFEFE while IP packets are either Ethernet II frames or SNAP frames identified with the protocol number 0x800. OSPF runs over IP as protocol number 89.

IS-IS runs directly over layer 2 and hence:

– cannot support virtual links unless some explicit tunneling is implemented

– packets are kept small so that they don’t require hop-by-hop fragmentation

– uses ATM/SNAP encapsulation on ATM but there are hacks to make it use VcMux encapsulation

– some operating systems that support IP networking have been implemented to differentiate Layer 3 packets in kernel. Such Oss require a lot of kernel modifications to support IS-IS for IP routing.

– can never be routed beyond the immediate next hop and hence shielded from IP spoofing and similar Denial of Service attacks

Reference: https://tools.ietf.org/html/draft-bhatia-manral-diff-isis-ospf-00

 

 

QUESTION 202

Which command do you use to connect a dense-mode domain to a sparse-mode multicast domain?

 

A.

none, because there is no such command

B.

ip pim spt-threshold infinity

C.

ip pim register dense-mode

D.

ip pim dense-mode proxy-register

 

Correct Answer: D

Explanation:

For IP PIM multicast, Cisco recommends Sparse-Mode over Dense-Mode. In the midst of our network migration, we have a new network operating in Sparse-Mode with Anycast rendezvous point (RP) but our existing network is still operating in Dense-Mode. To bridge two different modes across both PIM domains, we should use the ip pim dense-mode proxy-register command on the interface leading toward the bordering dense mode region. This configuration will enable the border router to register traffic from the dense mode region (which has no concept of registration) with the RP in the sparse mode domain.

Reference: http://networkerslog.blogspot.com/2010/12/bridging-dense-mode-pim-to-sparse-mode.html

 

 

QUESTION 203

Which two statements about the function of a PIM designated router are true? (Choose two.)

 

A.

It forwards multicast traffic from the source into the PIM network.

B.

It registers directly connected sources to the PIM rendezvous point.

C.

It sends PIM Join/Prune messages for directly connected receivers.

D.

It sends IGMP queries.

E.

It sends PIM asserts on the interfaces of the outgoing interface list.

 

Correct Answer: BC

Explanation:

In PIM ASM and SSM modes, the software chooses a designated router (DR) from the routers on each network segment. The DR is responsible for forwarding multicast data for specified groups and sources on that segment.

In ASM mode, the DR is responsible for unicasting PIM register packets to the RP. When a DR receives an IGMP membership report from a directly connected receiver, the shortest path is formed to the RP, which may or may not go through the DR. The result is a shared tree that connects all sources transmitting on the same multicast group to all receivers of that group. In SSM mode, the DR triggers (*, G) or (S, G) PIM join messages toward the RP or the source. The path from the receiver to the source is determined hop by hop. The source must be known to the receiver or the DR.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/multicast/configuration/guide/n7k_multic_cli_5x/pim.html#wp1054047

 

QUESTION 204

Refer to the exhibit. Which IP packets will be accepted from EBGP neighbor 10.1.1.1?

 

clip_image002

 

A.

IP packets with a TTL count in the header that is equal to or greater than 253

B.

IP packets with a TTL count in the header that is equal to 253

C.

IP packets with a TTL count in the header that is equal to or greater than 2

D.

IP packets with a TTL count in the header that is equal to 2

 

Correct Answer: A

Explanation:

neighbor ip-address ttl-security hops hop-count

Example:

Router(config-router)# neighbor 10.1.1.1 ttl-security hops 2

Configures the maximum number of hops that separate two peers.

 

The hop-count argument is set to number of hops that separate the local and remote peer. If the expected TTL value in the IP packet header is 254, then the number 1 should be configured for the hop-count argument. The range of values is a number from 1 to 254.

 

When this feature is enabled, BGP will accept incoming IP packets with a TTL value that is equal to or greater than the expected TTL value. Packets that are not accepted are silently discarded.

 

The example configuration sets the expected incoming TTL value to at least 253, which is 255 minus the TTL value of 2, and this is the minimum TTL value expected from the BGP peer. The local router will accept the peering session from the 10.1.1.1 neighbor only if it is 1 or 2 hops away.

 

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2s/feature/guide/fs_btsh.html

 

 

QUESTION 205

Which option is the default number of routes over which EIGRP can load balance?

 

A.

1

B.

4

C.

8

D.

16

 

Correct Answer: B

Explanation:

By default, EIGRP load-shares over four equal-cost paths. For load sharing to happen, the routes to load-share over must show up in the IP forwarding table or with the show ip route command. Only when a route shows up in the forwarding table with multiple paths to it will load sharing occur.

Reference: http://www.informit.com/library/content.aspx?b=CCIE_Practical_Studies_I&seqNum=126

 

 

 

QUESTION 206

Refer to the exhibit. A tunnel is configured between R3 to R4 sourced with their loopback interfaces. The ip pim sparse-dense mode command is configured on the tunnel interfaces and multicast-routing is enabled on R3 and R4. The IP backbone is not configured for multicast routing. The RPF check has failed toward the multicast source. Which two conditions could have caused the failure? (Choose two.)

 

clip_image004

 

A.

The route back to the RP is through a different interface than tunnel 0.

B.

The backbone devices can only route unicast traffic.

C.

The route back to the RP is through the same tunnel interface.

D.

A static route that points the RP to GigabitEthernet1/0 is configured.

 

Correct Answer: AD

Explanation:

For a successful RPF verification of multicast traffic flowing over the shared tree (*,G) from RP, an ip mroute rp-address nexthop command needs to be configured for the RP address, that points to the tunnel interface.

A very similar scenario can be found at the reference link below:

Reference: http://www.cisco.com/c/en/us/support/docs/ip/ip-multicast/43584-mcast-over-gre.html

 

 

QUESTION 207

When EIGRP is used as the IPv4 PE-CE protocol, which two requirements must be configured before the BGP IPv4 address family can be configured? (Choose two.)

 

A.

the route distinguisher

B.

the virtual routing and forwarding instance

C.

the loopback interface

D.

the router ID

 

Correct Answer: AB

Explanation:

A VRF must be created, and a route distinguisher and route target must be configured in order for the PE routers in the BGP network to carry EIGRP routes to the EIGRP CE site. The VRF must also be associated with an interface in order for the PE router to send routing updates to the CE router.

Prerequisites

Before this feature can be configured, MPLS and CEF must be configured in the BGP network, and multiprotocol BGP and EIGRP must be configured on all PE routers that provide VPN services to CE routers.

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/seipecec.html#wp1083316

 

 

QUESTION 208

Which three EIGRP packet types are valid? (Choose three.)

 

A.

open

B.

notification

C.

keep-alive

D.

hello

E.

query

F.

reply

 

Correct Answer: DEF

Explanation:

EIGRP uses the following packet types: hello and acknowledgment, update, and query and reply. Hello packets are multicast for neighbor discovery/recovery and do not require acknowledgment. An acknowledgment packet is a hello packet that has no data. Acknowledgment packets contain a nonzero acknowledgment number and always are sent by using a unicast address. Update packets are used to convey reachability of destinations. When a new neighbor is discovered, unicast update packets are sent so that the neighbor can build up its topology table. In other cases, such as a link-cost change, updates are multicast. Updates always are transmitted reliably.

Query and reply packets are sent when a destination has no feasible successors. Query packets are always multicast. Reply packets are sent in response to query packets to instruct the originator not to recompute the route because feasible successors exist. Reply packets are unicast to the originator of the query. Both query and reply packets are transmitted reliably.

Reference: http://docwiki.cisco.com/wiki/Enhanced_Interior_Gateway_Routing_Protocol

 

 

QUESTION 209

Which term describes an EIGRP route that has feasible successors?

 

A.

active

B.

passive

C.

redistributed

D.

invalid

 

Correct Answer: B

Explanation: Explanation”

A topology table entry for a destination can have one of two states. A route is considered in the Passive state when a router is not performing a route recomputation. The route is in Active state when a router is undergoing a route recomputation. If there are always feasible successors, a route never has to go into Active state and avoids a route recomputation.

 

When there are no feasible successors, a route goes into Active state and a route recomputation occurs. A route recomputation commences with a router sending a query packet to all neighbors. Neighboring routers can either reply if they have feasible successors for the destination or optionally return a query indicating that they are performing a route recomputation. While in Active state, a router cannot change the next-hop neighbor it is using to forward packets. Once all replies are received for a given query, the destination can transition to Passive state and a new successor can be selected.

Reference: http://docwiki.cisco.com/wiki/Enhanced_Interior_Gateway_Routing_Protocol

 

 

QUESTION 210

Refer to the exhibit. If EIGRP is configured between two routers as shown in this output, which statement about their EIGRP relationship is true?

 

clip_image006

 

A.

The routers will establish an EIGRP relationship successfully.

B.

The routers are using different authentication key-strings.

C.

The reliability metric is enabled.

D.

The delay metric is disabled.

 

Correct Answer: C

Explanation:

The 5 K values used in EIGRP are:

K1 = Bandwidth modifier

K2 = Load modifier

K3 = Delay modifier

K4 = Reliability modifier

K5 = Additional Reliability modifier

 

However, by default, only K1 and K3 are used (bandwidth and delay). In this output we see that K1, K3, and K4 (Reliability) are all set.

 

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