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Q471. Which two statements describe characteristics of HDLC on Cisco routers? (Choose two.) 

A. It supports multiple Layer 3 protocols. 

B. It supports multiplexing. 

C. It supports only synchronous interfaces. 

D. It supports authentication. 

Answer: A,C 

Explanation: 

Cisco High-Level Data Link Controller (HDLC) is the Cisco proprietary protocol for sending data over synchronous serial links using HDLC. Cisco HDLC also provides a simple control protocol called Serial Line Address Resolution Protocol (SLARP) to maintain serial link keepalives. Cisco HDLC is the default for data encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack for efficient packet delineation and error control. The absence of a protocol type field in the HDLC header posed a problem for links that carried traffic from more than one Layer 3 protocol. Cisco, therefore, added an extra Type field to the HDLC header, creating a Cisco-specific version of HDLC. Cisco routers can support multiple network layer protocols on the same HDLC link. For example an HDLC link between two Cisco routers can forward both IPv4 and IPv6 packets because the Type field can identify which type of packet is carried inside each HDLC frame. 

Reference: http://www.cisco.com/c/en/us/td/docs/routers/access/800/819/software/configuration/Guide/ 

819_SCG/6ser_conf.html#pgfId-1073734 


Q472. Which three options must be configured when deploying OSPFv3 for authentication? (Choose three.) 

A. security parameter index 

B. crypto map 

C. authentication method 

D. IPsec peer 

E. encryption algorithm 

F. encryption key 

G. IPsec transform-set 

H. authentication key 

Answer: A,C,H 


Q473. Refer to the exhibit. 

Which two issues can cause the interface VLAN10 to be down/down? (Choose two.) 

A. The VLAN is inactive or has been removed from the VLAN database. 

B. STP is in a forwarding state on the port. 

C. A Layer 2 access port is configured with VLAN10, but is in a down/down state. 

D. The autostate exclude feature was used on interface VLAN10. 

Answer: A,C 


Q474. Refer to the exhibit. 

Which statement about configuring the switch to manage traffic is true? 

A. The switchport priority extend cos command on interface FastEthernet0/0 prevents traffic to and from the PC from taking advantage of the high-priority data queue that is assigned to the IP phone. 

B. The switchport priority extend cos command on interface FastEthernet0/0 enables traffic to and from the PC to use the high priority data queue that is assigned to the IP phone. 

C. When the switch is configured to trust the CoS label of incoming traffic, the trusted boundary feature is disabled automatically. 

D. The mls qos cos override command on interface FastEthernet0/0 configures the port to trust the CoS label of traffic to and from the PC. 

Answer:

Explanation: 

In some situations, you can prevent a PC connected to the Cisco IP Phone from taking advantage of a high-priority data queue. You can use the switchport priority extend cos interface configuration command to configure the telephone through the switch CLI to override the priority of the traffic received from the PC. 

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2950/software/release/12-1_22_ea2/configuration/guide/2950scg/swqos.html 


Q475. EIGRP allows configuration of multiple MD5 keys for packet authentication to support easy rollover from an old key to a new key. Which two statements are true regarding the usage of multiple authentication keys? (Choose two.) 

A. Received packets are authenticated by the key with the smallest key ID. 

B. Sent packets are authenticated by all valid keys, which means that each packet is replicated as many times as the number of existing valid keys. 

C. Received packets are authenticated by any valid key that is chosen. 

D. Sent packets are authenticated by the key with the smallest key ID. 

Answer: C,D 

Explanation: 

Suppose two routers are connected with each other via Fa0/0 interfaces and they are configured to authenticate via MD5. Below is a simple configuration on both routers so that they will work: 

Router1(config)#key chain KeyChainR1 

Router1(config-keychain)#key 1 

Router1(config-keychain-key)#key-string FirstKey 

Router1(config-keychain-key)#key 2 

Router1(config-keychain-key)#key-string SecondKey 

Router2(config)#key chain KeyChainR2 

Router2(config-keychain)#key 1 

Router2(config-keychain-key)#key-string FirstKey 

Router2(config-keychain-key)#key 2 

Router2(config-keychain-key)#key-string SecondKey 

Apply these key chains to R1 & R2: 

Router1(config)#interface fastEthernet 0/0 

Router1(config-if)#ip authentication mode eigrp 1 md5 

Router1(config-if)#ip authentication key-chain eigrp 1 KeyChainR1 

Router2(config)#interface fastEthernet 0/0 

Router2(config-if)#ip authentication mode eigrp 1 md5 

Router2(config-if)#ip authentication key-chain eigrp 1 KeyChainR2 

There are some rules to configure MD5 authentication with EIGRP: 

+ The key chain names on two routers do not have to match (in this case the name “KeyChainR1 & “KeyChainR2 do not match) 

+ The key number and key-string on the two potential neighbors must match (for example “key 1 & “key-string FirstKey” must match on “key 1” & “key-string FirstKey” of neighboring router) Also some facts about MD5 authentication with EIGRP 

+ When sending EIGRP messages the lowest valid key number is used -> D is correct. 

+ When receving EIGRP messages all currently configured valid keys are verified but the lowest valid one will be used -> Although answer C does not totally mention like that but it is the most suitable answer because A and B are totally wrong. Answer A is not correct because we need valid key to authenticate. As mentioned above, although answer C is not totally correct but it puts some light on why 

answer B is not correct: each packet is NOT “replicated as many times as the number of existing valid keys”. All currently configured valid keys are verified but the lowest valid one will be used. 


Update 400-101 practice question:

Q476. As a best practice, when a router is configured as an EIGRP Stub, which routes should be received from its distribution neighbor? 

A. the default route 

B. static routes 

C. internal routes only 

D. internal and external routes 

Answer:

Explanation: 

Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the distribution router need not send anything more than a default route to the remote router. 

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


Q477. Which two hashing algorithms can be used when configuring SNMPv3? (Choose two.) 

A. MD5 

B. SHA-1 

C. Blowfish 

D. DES 

E. AES 

F. SSL 

Answer: A,B 

Explanation: 

Note that SNMPv3 does not send passwords in clear-text and uses hash-based authentication with either MD5 or SHA1 functions (HMAC authentication – the packet conted is hashed along with authentication key to produce the authentication string). 

Reference: http://blog.ine.com/2008/07/19/snmpv3-tutorial/ 


Q478. 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 

Answer: D,E 

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: 

. Hello interval 

. Dead interval 

. Area ID 

. 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 


Q479. Which three values can you use to configure an ERSPAN destination session? (Choose three.) 

A. VLAN ID 

B. source IP address 

C. destination IP address 

D. ID number 

E. VRF 

F. session name 

Answer: B,D,E 


Q480. DRAG DROP 

Drag and drop the StackWise stack master election rule on the left into the correct priority order on the right. 

Answer: