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CCIE Routing and Switching Written Exam v5.1

 

QUESTION 251

Which two statements about the default router settings for SSH connections are true? (Choose two.)

 

A.

The default timeout value for the SSH negotiation phase is 120 seconds.

B.

Data is exchanged in clear text by default unless AAA authentication is enabled on the console.

C.

The default number of authentication retries is 3.

D.

SSH is enabled by default when you configure the username command.

 

Correct Answer: AC

Explanation:

ip ssh {timeout seconds | authentication-retries number}

Configures the SSH control parameters:

Specify the time-out value in seconds; the default is 120 seconds. The range is 0 to 120 seconds. This parameter applies to the SSH negotiation phase. After the connection is established, the Switch uses the default time-out values of the CLIbased sessions. By default, up to five simultaneous, encrypted SSH connections for multiple CLI-based sessions over the network are available (session 0 to session 4). After the execution shell starts, the CLI-based session time-out value returns to the default of 10 minutes.

Specify the number of times that a client can re-authenticate to the server. The default is 3; the range is 0 to 5.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/security/conf iguration_guide/b_sec_3se_3850_cg/b_sec_3se_3850_cg_chapter_01000.html

 

 

QUESTION 252

Which service is disabled by the no service tcp-small-servers command?

 

A.

the finger service

B.

the Telnet service

C.

the Maintenance Operation Protocol service

D.

the chargen service

 

Correct Answer: D

Explanation:

The TCP small servers are:

Echo: Echoes back whatever you type through the telnet x.x.x.x echo command.

Chargen: Generates a stream of ASCII data. Use the telnet x.x.x.x chargen command.

Discard: Throws away whatever you type. Use the telnet x.x.x.x discard command.

Daytime: Returns system date and time, if it is correct. It is correct if you run Network Time Protocol (NTP), or have set the date and time manually from the exec level. Use the telnet x.x.x.x daytime command.

 

Reference: http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-110/12815-23.html

 

 

 

 

 

QUESTION 253

Which two statements about proxy ARP are true? (Choose two.)

 

A.

It is supported on networks without ARP.

B.

It allows machines to spoof packets.

C.

It requires larger ARP tables

D.

It reduces the amount of ARP traffic.

E.

It must be used on a network with the host on a different subnet.

 

Correct Answer: BC

Explanation:

Disadvantages of Proxy ARP

Hosts have no idea of the physical details of their network and assume it to be a flat network in which they can reach any destination simply by sending an ARP request. But using ARP for everything has disadvantages. These are some of the disadvantages:

It increases the amount of ARP traffic on your segment.

Hosts need larger ARP tables in order to handle IP-to-MAC address mappings.

Security can be undermined. A machine can claim to be another in order to intercept packets, an act called “spoofing.”

It does not work for networks that do not use ARP for address resolution.

It does not generalize to all network topologies. For example, more than one router that connects two physical networks.

 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/13718-5.html

 

 

QUESTION 254

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 255

Which two actions can you take to allow the greatest number of pertinent packets to be stored in the temporary buffer of Cisco IOS Embedded Packet Capture? (Choose two.)

 

A.

Specify the sampling interval.

B.

Specify the capture buffer type.

C.

Specify a reflexive ACL.

D.

Specify the minimum packet capture rate.

E.

Specify the packet size.

F.

Store the capture simultaneously onto an external memory card as the capture occurs.

Correct Answer: AB

Explanation:

Embedded Packet Capture (EPC) provides an embedded systems management facility that helps in tracing and troubleshooting packets. This feature allows network administrators to capture data packets flowing through, to, and from a Cisco device. The network administrator may define the capture buffer size and type (circular, or linear) and the maximum number of bytes of each packet to capture. The packet capture rate can be throttled using further administrative controls. For example, options allow for filtering the packets to be captured using an Access Control List and, optionally, further defined by specifying a maximum packet capture rate or by specifying a sampling interval.

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/epc/configuration/xe-3s/asr1000/epc-xe-3s-asr1000-book/nm-packet-capture-xe.html

 

 

QUESTION 256

DRAG DROP

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Correct Answer:

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QUESTION 257

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 258

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

 

clip_image006

 

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 259

If two OSPF type 3 prefixes have the same metric, and are within the same process, which prefix(es) are installed into the routing table?

 

A.

The route whose originator has the lower router ID.

B.

Both routes are installed.

C.

The route whose originator has the higher router ID.

D.

The first route that is learned.

 

Correct Answer: B

Explanation:

OSPF allows multiple equal-cost paths to the same destination. Since all link-state information is flooded and used in the SPF calculation, multiple equal cost paths can be computed and used for routing, and each route will be installed in the routing table.

 

 

QUESTION 260

Which BGP aggregate address configuration advertises only the aggregate address, with attributes inherited from the more specific routes?

 

A.

summary-only as-set

B.

as-set

C.

summary

D.

summary-only

 

Correct Answer: A

Explanation:

Example:

router bgp 300

neighbor 2.2.2.2 remote-as 100

neighbor 3.3.3.3 remote-as 200

neighbor 4.4.4.4 remote-as 400

aggregate-address 160.0.0.0 255.0.0.0 summary-only as-set

 

!— With the as-set configuration command, the aggregate

!— inherits the attributes of the more-specific routes.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5441-aggregation.html

 

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