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Q271. When the BGP additional-paths feature is used, what allows a BGP speaker to differentiate between the different available paths?
A. The remote BGP peer prepends its own next-hop address to the prefix.
B. A unique path identifier is encoded into a dedicated field to the NLRI.
C. A route distinguisher is appended to the prefix by the receiving BGP speaker.
D. The additional path information is encoded in an extended community.
Answer: B
Q272. Which IPv6 prefix is used for 6to4 tunnel addresses?
A. 2001::/23
B. 2002::/16
C. 3ffe::/16
D. 5f00::/8
E. 2001::/32
Answer: B
Explanation:
6to4 works by taking advantage of a reserved IPv6 prefix, 2002::/16. A 6to4 tunnel interface automatically converts the 32 bits in its IPv6 address following this prefix to a global unicast IPv4 address for transport across an IPv4 network such as the public Internet.
Reference: http://packetlife.net/blog/2010/mar/15/6to4-ipv6-tunneling/
Q273. Which two statements about Cisco Express Forwarding are true? (Choose two.)
A. Cisco Express Forwarding tables contain reachability information and adjacency tables contain forwarding information.
B. Cisco Express Forwarding tables contain forwarding information and adjacency tables contain reachability information.
C. Changing MAC header rewrite strings requires cache validation.
D. Adjacency tables and Cisco Express Forwarding tables can be built separately.
E. Adjacency tables and Cisco Express Forwarding tables require packet process-switching.
Answer: A,D
Explanation:
Main Components of CEF
Information conventionally stored in a route cache is stored in several data structures for Cisco Express Forwarding switching. The data structures provide optimized lookup for efficient packet forwarding. The two main components of Cisco Express Forwarding operation are the forwarding information base (FIB) and the adjacency tables. The FIB is conceptually similar to a routing table or information base. A router uses this lookup table to make destination-based switching decisions during Cisco Express Forwarding operation. The FIB is updated when changes occur in the network and contains all routes known at the time. Adjacency tables maintain Layer 2 next-hop addresses for all FIB entries. This separation of the reachability information (in the Cisco Express Forwarding table) and the forwarding information (in the adjacency table), provides a number of benefits:
. The adjacency table can be built separately from the Cisco Express Forwarding table, allowing both to be built without any packets being process-switched.
. The MAC header rewrite used to forward a packet is not stored in cache entries, so changes in a MAC header rewrite string do not require validation of cache entries.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipswitch_cef/configuration/15-mt/isw-cef-15-mt-book/isw-cef-overview.html
Q274. 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.
Answer: A,C
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 form 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.
Q275. DRAG DROP
Drag and drop the multicast protocol definition on the left to the correct default time interval on the right.
Answer:
Q276. Which statement about OSPF loop prevention is true?
A. The discard route is generated automatically on the ABR to prevent routing loops.
B. The ASBR uses type 3 LSAs from non-backbone areas to prevent control-plane routing loops.
C. The ABR can filter type 3 LSPs to prevent routing loops.
D. The DN bit ignores LSA types 2, 3, and 5 to prevent routing loops.
Answer: A
Q277. Refer to the exhibit.
Which two options are possible states for the interface configured with the given OSPFv3
authentication? (Choose two.)
A. GOING UP
B. DOWN
C. UNCONFIGURED
D. GOING DOWN
Answer: A,B
Explanation:
To configure IPsec, you configure a security policy, which is a combination of the security policy index (SPI) and the key (the key is used to create and validate the hash value). IPsec for OSPFv3 can be configured on an interface or on an OSPFv3 area. For higher security, you should configure a different policy on each interface configured with IPsec. If you configure IPsec for an OSPFv3 area, the policy is applied to all of the interfaces in that area, except for the interfaces that have IPsec configured directly. Once IPsec is configured for OSPFv3, IPsec is invisible to you. The secure socket API is used by applications to secure traffic. The API needs to allow the application to open, listen, and close secure sockets. The binding between the application and the secure socket layer also allows the secure socket layer to inform the application of changes to the socket, such as connection open and close events. The secure socket API is able to identify the socket; that is, it can identify the local and remote addresses, masks, ports, and protocol that carry the traffic requiring security. Each interface has a secure socket state, which can be one of the following:
. NULL: Do not create a secure socket for the interface if authentication is configured for the area.
. DOWN: IPsec has been configured for the interface (or the area that contains the interface), but OSPFv3 either has not requested IPsec to create a secure socket for this interface, or there is an error condition.
. GOING UP: OSPFv3 has requested a secure socket from IPsec and is waiting for a CRYPTO_SS_SOCKET_UP message from IPsec.
. UP: OSPFv3 has received a CRYPTO_SS_SOCKET_UP message from IPsec.
. CLOSING: The secure socket for the interface has been closed. A new socket may be opened for the interface, in which case the current secure socket makes the transition to the DOWN state. Otherwise, the interface will become UNCONFIGURED.
. UNCONFIGURED. Authentication is not configured on the interface.
OSPFv3 will not send or accept packets while in the DOWN state.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-sy/iro-15-sy-book/ip6-route-ospfv3-auth-ipsec.html
Q278. Refer to the exhibit.
What is the meaning of the asterisk (*) in the output?
A. PIM neighbor 10.1.5.6 is the RPF neighbor for the group 232.1.1.1 for the shared tree.
B. PIM neighbor 10.1.5.6 is the one that is seen as the RPF neighbor when performing the command show ip rpf 10.1.4.7.
C. PIM neighbor 10.1.5.6 is the winner of an assert mechanism.
D. The RPF neighbor 10.1.5.6 is invalid.
Answer: C
Explanation:
show ip mroute
Field
Descriptions
Field Description
RPF neighbor or RPF nbr
IP address of the upstream router to the source. Tunneling indicates that this router is sending data to the RP encapsulated in register packets.
The hexadecimal number in parentheses indicates to which RP it is registering. Each bit indicates a different RP if multiple RPs per group are used. If an asterisk (*) appears after the IP address in this field, the RPF neighbor has been learned through an assert.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/ipmulti/command/reference/fiprmc_r/1rfmult 3.html
Q279. Refer to the exhibit.
R3 prefers the path through R1 to reach host 10.1.1.1.
Which option describes the reason for this behavior?
A. The OSPF reference bandwidth is too small to account for the higher speed links through R2.
B. The default OSPF cost through R1 is less than the cost through R2.
C. The default OSPF cost through R1 is more than the cost through R2.
D. The link between R2 and R1 is congested.
Answer: A
Explanation:
The default formula to calculate OSPF bandwidth is BW = Bandwidth Reference / interface
bandwidth [bps] = 10^8 / / interface bandwidth [bps]
BW of the R1-R3 link = 10^8 / 100Mbps = 10^8 / 10^8 = 1
BW of the R2-R3 link = 10^8 / 1Gbps = 10^8 / 10^9 = 1 (round up)
Therefore OSPF considers the two above links have the same Bandwidth -> R3 will go to 10.1.1.1 via the R1-R3 link. The solution here is to increase the Bandwidth Reference to a higher value using the “auto-cost reference-bandwidth” command under OSPF router mode. For example: Router(config)#router ospf 1 Router(config-router)#auto-cost reference-bandwidth 10000 This will increase the reference bandwidth to 10000 Mbps which increases the BW of the R2-R3 link to 10^10 / 10^8 = 100.
Q280. Which two statements about BGP prefix-based outbound filtering are true? (Choose two.)
A. It must be configured per address family.
B. It can use prefix lists and route maps for filtering.
C. It can be configured under the global BGP routing process.
D. It can be configured for external peering sessions only.
E. It can increase the processing load on the router.
F. It supports IP multicast routes.
Answer: A,D
