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Q481. Which technology can be used to prevent flooding of IPv6 multicast traffic on a switch?
A. IGMP snooping
B. IGMP filtering
C. MLD snooping
D. MLD filtering
Answer: C
Explanation:
MLD snooping allows the switch to examine MLD packets and make forwarding decisions based on their content. You can configure the switch to use MLD snooping in subnets that receive MLD queries from either MLD or the MLD snooping querier. MLD snooping constrains IPv6 multicast traffic at Layer 2 by configuring Layer 2 LAN ports dynamically to forward IPv6 multicast traffic only to those ports that want to receive it.
Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/snoopmld.html
Q482. Which statement about the overload bit in IS-IS is true?
A. The IS-IS adjacencies on the links for which the overload bit is set are brought down.
B. Routers running SPF ignore LSPs with the overload bit set and hence avoid blackholing traffic.
C. A router setting the overload bit becomes unreachable to all other routers in the IS-IS area.
D. The overload bit in IS-IS is used only for external prefixes.
Answer: B
Explanation:
The OL bit is used to prevent unintentional blackholing of packets in BGP transit networks. Due to the nature of these protocols, IS-IS and OSPF converge must faster than BGP. Thus there is a possibility that while the IGP has converged, IBGP is still learning the routes. In that case if other IBGP routers start sending traffic towards this IBGP router that has not yet completely converged it will start dropping traffic. This is because it isnt yet aware of the complete BGP routes. OL bit comes handy in such situations. When a new IBGP neighbor is added or a router restarts, the IS-IS OL bit is set. Since directly connected (including loopbacks) addresses on an “overloaded” router are considered by other routers, IBGP can be bought up and can begin exchanging routes. Other routers will not use this router for transit traffic and will route the packets out through an alternate path. Once BGP has converged, the OL bit is cleared and this router can begin forwarding transit traffic.
Reference: https://routingfreak.wordpress.com/category/ospf-vs-is-is/
Q483. Which switching technology can be used to solve reliability problems in a switched network?
A. fragment-free mode
B. cut-through mode
C. check mode
D. store-and-forward mode
Answer: D
Explanation:
Characteristics of Store-and-Forward Ethernet Switching
This section provides an overview of the functions and features of store-and-forward Ethernet switches.
Error Checking
Figure 1 shows a store-and-forward switch receiving an Ethernet frame in its entirety. At the end of that frame, the switch will compare the last field of the datagram against its own frame-check-sequence (FCS) calculations, to help ensure that the packet is free of physical and data-link errors. The switch then performs the forwarding process. Whereas a store-and-forward switch solves reliability issues by dropping invalid packets, cut-through devices forward them because they do not get a chance to evaluate the FCS before transmitting the packet.
Figure 1. Ethernet Frame Entering a Store-and-Forward Bridge or Switch (from Left to Right)
Reference: http://www.cisco.com/c/en/us/products/collateral/switches/nexus-5020-switch/white_paper_c11-465436.html
Q484. Refer to the exhibit.
While troubleshooting high CPU utilization of a Cisco Catalyst 4500 Series Switch, you notice the error message that is shown in the exhibit in the log file.
What can be the cause of this issue, and how can it be prevented?
A. The hardware routing table is full. Redistribute from BGP into IGP.
B. The software routing table is full. Redistribute from BGP into IGP.
C. The hardware routing table is full. Reduce the number of routes in the routing table.
D. The software routing table is full. Reduce the number of routes in the routing table.
Answer: C
Explanation:
L3HWFORWADING-2
Error MessageC4K_L3HWFORWARDING-2-FWDCAMFULL:L3 routing table is full.
Switching to software forwarding.
The hardware routing table is full; forwarding takes place in the software instead. The switch performance might be degraded.
Recommended Action: Reduce the size of the routing table. Enter the ip cef command to return to hardware forwarding.
Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/31sg/system/message/message/emsg.html
Q485. Which two statements about the ipv6 ospf authentication command are true? (Choose two.)
A. The command is required if you implement the IPsec AH header.
B. The command configures an SPI.
C. The command is required if you implement the IPsec TLV.
D. The command can be used in conjunction with the SPI authentication algorithm.
E. The command must be configured under the OSPFv3 process.
Answer: A,B
Explanation:
OSPFv3 requires the use of IPsec to enable authentication. Crypto images are required to use authentication, because only crypto images include the IPsec API needed for use with OSPFv3. In OSPFv3, authentication fields have been removed from OSPFv3 packet headers. When OSPFv3 runs on IPv6, OSPFv3 requires the IPv6 authentication header (AH) or IPv6 ESP header to ensure integrity, authentication, and confidentiality of routing exchanges. IPv6 AH and ESP extension headers can be used to provide authentication and confidentiality to OSPFv3. To use the IPsec AH, you must enable the ipv6 ospf authentication command. To use the IPsec ESP header, you must enable the ipv6 ospf encryption command. The ESP header may be applied alone or in combination with the AH, and when ESP is used, both encryption and authentication are provided. Security services can be provided between a pair of communicating hosts, between a pair of communicating security gateways, or between a security gateway and a host. 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.
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
Q486. What is the new designation for the MPLS EXP (experimental) bits?
A. QoS bits
B. traffic class bits
C. flow bits
D. precedence bits
Answer: B
Explanation:
To avoid misunderstanding about how this field may be used, it has become increasingly necessary to rename this field. This document changes the name of the EXP field to the "Traffic Class field" ("TC field"). In doing so, it also updates documents that define the current use of the EXP field.
Reference: https://tools.ietf.org/html/rfc5462
Q487. Independent, multiple OSPF processes are entered on the same router, and the processes have the same destination route. Which OSPF process is used?
A. The route with the fewest hops is used.
B. Both processes are used to load balance the traffic.
C. The first route process that places a route into the routing table is used.
D. The route with the shortest prefix is used.
Answer: C
Q488. Refer to the exhibit.
The interface FastEthernet0/1 of both routers R4 and R5 is connected to the same Ethernet segment with a multicast receiver. Which two statements are true? (Choose two)
A. Multicast traffic that is destined to a receiver with IP address 192.168.2.6 will flow through router R4.
B. Both routers R4 and R5 will send PIM join messages to the RP.
C. Only router R5 will send a multicast join message to the RP.
D. Multicast traffic that is destined to a receiver with IP address 192.168.2.6 will flow through router R5.
Answer: C,D
Explanation:
Even though R4 is the active HSRP router, traffic will flow through R5 and only R5 will send the join messages. The Multicast DR is elected by the higher IP address or priority. R5 has 192.168.2.2 and R4 has 192.168.2.1. R5 is the DR which sends all packets to the RP.
Q489. A packet capture log indicates that several router solicitation messages were sent from a local host on the IPv6 segment. What is the expected acknowledgment and its usage?
A. Router acknowledgment messages will be forwarded upstream, where the DHCP server will allocate addresses to the local host.
B. Routers on the IPv6 segment will respond with an advertisement that provides an external path from the local subnet, as well as certain data, such as prefix discovery.
C. Duplicate Address Detection will determine if any other local host is using the same IPv6 address for communication with the IPv6 routers on the segment.
D. All local host traffic will be redirected to the router with the lowest ICMPv6 signature, which is statically defined by the network administrator.
Answer: B
Q490. Refer to the exhibit.
Why is the neighbor relationship between R2 and R4 shown as ES-IS?
A. because there is an MTU mismatch between R2 and R4
B. because interface S3/0 of R4 is configured as L1/L2
C. because interface S3/0 of R2 is configured as L1
D. because there is a hello interval mismatch between R2 and R4
Answer: C
Explanation:
With IS-IS we will see ES-IS when one of the following is true:
. uk.co.certification.simulator.questionpool.PList@138b7160
So in this question because we do not know about the other side’s “show CLNS neighbor” A must be the better choose.
