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Q281. How does having an EIGRP feasible successor speed up convergence?
A. EIGRP sends queries only if there is a feasible successor, which decreases the number of routers that are involved in convergence.
B. EIGRP sends queries only if there is not a feasible successor, which causes less control traffic to compete with data.
C. EIGRP immediately installs the loop-free alternative path in the RIB.
D. EIGRP preinstalls the feasible successor in the RIB in all cases, which causes traffic to switch more quickly.
Answer: C
Explanation:
Feasible Successor
. A next-hop router that serves as backup to the current successor.
. The condition is that the said router’s AD (or RD) is less than the FD of the current successor route.
. Once the feasible successor is selected, they are placed in the topology table. If a change in topology occurs which requires a new route, DUAL looks for the feasible successor and uses it as new route immediately, resulting in fast convergence.
Reference: http://routemyworld.com/2008/07/page/2/
Q282. Refer to the exhibit.
You are configuring the S1 switch for the switchport connecting to the client computer. Which option describes the effect of the command mls qos map cos-dscp 0 8 16 24 32 40 46 56?
A. Voice traffic is excluded from the default priority queue.
B. Voice packets are given a class selector of 5.
C. Video conferencing is marked CS3.
D. Voice packets are processed in the priority queue.
Answer: A
Explanation:
The default CoS to DSCP mappings are shown below:
Default CoS-to-DSCP Map
CoS Value
DSCP Value
0
0
1
8
2
16
3
24
4
32
5
40
6
48
7
56
In our example, we see that COS 6 is mapped to DSCP, not the default of DSCP 48 as shown above. DSCP 46 is Expedited Forwarding (EF), which is typically used for voice traffic, and this value has not been included in this class map.
Q283. Which CoS value is mapped to DSCP 48 by default?
A. 6
B. 7
C. AF21
D. AF44
E. AF41
F. 46
Answer: A
Q284. Which two options are reasons to manipulate the delay metric instead of the bandwidth metric for EIGRP routing? (Choose two.)
A. Because the delay metric provides better handling for bursty traffic
B. Because manipulating the bandwidth metric can also affect QoS
C. Because manipulating the bandwidth affects only a particular path
D. Because changes to the delay metric are propagated to all neighbors on a segment
Answer: B,D
Explanation:
Using the bandwidth to influence EIGRP paths is discouraged for two reasons:
. Changing the bandwidth can have impact beyond affecting the EIGRP metrics. For example, quality of service (QoS) also looks at the bandwidth on an interface.
. EIGRP throttles to use 50 percent of the configured bandwidth. Lowering the bandwidth can cause problems like staving EIGRP neighbors from getting hello packets because of the throttling back.
Because changes to the delay metric are propagated to all downstream routers, changing the interface delay parameter is the preferred method of influencing path selection
Reference: http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13673-14.html
Q285. Which value is the maximum segment size if you start with an MTU of 1500 bytes and then remove the overhead of the Ethernet header, IP header, TCP header, and the MAC frame check sequence?
A. 1434 bytes
B. 1460 bytes
C. 1458 bytes
D. 1464 bytes
Answer: B
Q286. Which statement about the OSPF Loop-Free Alternate feature is true?
A. It is supported on routers that are configured with virtual links.
B. It is supported in VRF OSPF instances.
C. It is supported when a traffic engineering tunnel interface is protected.
D. It is supported when traffic can be redirected to a primary neighbor.
Answer: B
Explanation:
Restrictions for OSPF IPv4 Remote Loop-Free Alternate IP Fast Reroute
. The OSPF IPv4 Remote Loop-Free Alternate IP Fast Reroute feature is not supported on devices that are virtual links headends.
. The feature is supported only in global VPN routing and forwarding (VRF) OSPF
Instances.
. The only supported tunneling method is MPLS.
. You cannot configure a traffic engineering (TE) tunnel interface as a protected interface. Use the MPLS Traffic Engineering—Fast Reroute Link and Node Protection feature to protect these tunnels. For more information, see the “MPLS Traffic Engineering—Fast Reroute Link and Node Protection” section in the Multiprotocol Label Switching Configuration Guide.
. You can configure a TE tunnel interface in a repair path, but OSPF will not verify the tunnel’s placement; you must ensure that it is not crossing the physical interface that it is intended to protect.
. Not all routes can have repair paths. Multipath primary routes might have repair paths for all, some, or no primary paths, depending on the network topology, the connectivity of the computing router, and the attributes required of repair paths.
. Devices that can be selected as tunnel termination points must have a /32 address advertised in the area in which remote LFA is enabled. This address will be used as a tunnel termination IP. If the device does not advertise a /32 address, it may not be used for remote LFA tunnel termination.
. All devices in the network that can be selected as tunnel termination points must be configured to accept targeted LDP sessions using the mpls ldp discovery targeted-hello accept command.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-3s/iro-xe-3s-book/iro-ipfrr-lfa.html
Q287. Refer to the exhibit.
Which two statements about the output are true? (Choose two.)
A. 802.1D spanning tree is being used.
B. Setting the priority of this switch to 0 for VLAN 1 would cause it to become the new root.
C. The hello, max-age, and forward delay timers are not set to their default values.
D. Spanning-tree PortFast is enabled on GigabitEthernet1/1.
Answer: A,B
Explanation:
802.1D is the standard for Spanning tree, which is being used here. For priority, The priority order starts from 0 (yes, 0 is valid) and then increases in 4096. 0, 4096, 8192, 12288, …. Etc.
The lower the number is, the higher is the priority. Here we see that the current root has a priority of 8192, so configuring this with a priority of 0 will make it the new root.
Q288. Which two options are reasons for TCP starvation? (Choose two.)
A. The use of tail drop
B. The use of WRED
C. Mixing TCP and UDP traffic in the same traffic class
D. The use of TCP congestion control
Answer: C,D
Explanation:
It is a general best practice to not mix TCP-based traffic with UDP-based traffic (especially Streaming-Video) within a single service-provider class because of the behaviors of these protocols during periods of congestion. Specifically, TCP transmitters throttle back flows when drops are detected. Although some UDP applications have application-level windowing, flow control, and retransmission capabilities, most UDP transmitters are completely oblivious to drops and, thus, never lower transmission rates because of dropping. When TCP flows are combined with UDP flows within a single service-provider class and the class experiences congestion, TCP flows continually lower their transmission rates, potentially giving up their bandwidth to UDP flows that are oblivious to drops. This effect is called TCP starvation/UDP dominance. TCP starvation/UDP dominance likely occurs if (TCP-based) Mission-Critical Data is assigned to the same service-provider class as (UDP-based) Streaming-Video and the class experiences sustained congestion. Even if WRED or other TCP congestion control mechanisms are enabled on the service-provider class, the same behavior would be observed because WRED (for the most part) manages congestion only on TCP-based flows.
Reference: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/Qo S-SRND-Book/VPNQoS.html
Q289. Which statement describes the BGP add-path feature?
A. It allows for installing multiple IBGP and EBGP routes in the routing table.
B. It allows a network engineer to override the selected BGP path with an additional path created in the config.
C. It allows BGP to provide backup paths to the routing table for quicker convergence.
D. It allows multiple paths for the same prefix to be advertised.
Answer: D
Explanation:
BGP routers and route reflectors (RRs) propagate only their best path over their sessions. The advertisement of a prefix replaces the previous announcement of that prefix (this behavior is known as an implicit withdraw). The implicit withdraw can achieve better scaling, but at the cost of path diversity. Path hiding can prevent efficient use of BGP multipath, prevent hitless planned maintenance, and can lead to MED oscillations and suboptimal hot-potato routing. Upon nexthop failures, path hiding also inhibits fast and local recovery because the network has to wait for BGP control plane convergence to restore traffic. The BGP Additional Paths feature provides a generic way of offering path diversity; the Best External or Best Internal features offer path diversity only in limited scenarios. The BGP Additional Paths feature provides a way for multiple paths for the same prefix to be advertised without the new paths implicitly replacing the previous paths. Thus, path diversity is achieved instead of path hiding.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3s-book/irg-additional-paths.html
Q290. Refer to the exhibit.
Router 1 and Router 2 use HSRP to provide first hop redundancy for hosts on the 10.1.2.0/24 network.
Which feature can provide additional failover coverage for the PC?
A. Cisco Express Forwarding
B. NetFlow
C. Accounting
D. Enhanced Object Tracking
Answer: D
Explanation:
HSRP has a mechanism for tracking the interface line-protocol state. The enhanced object tracking feature separates the tracking mechanism from HSRP. It creates a separate, standalone tracking process that can be used by processes other than HSRP. This feature allows tracking of other objects in addition to the interface line-protocol state. A client process, such as HSRP, can register an interest in tracking objects and request notification when the tracked object changes state. Several clients can track the same object, and can take different actions when the object changes state. This feature increases the availability and speed of recovery of a router system and decreases outages and outage duration.
Reference: http://www.cisco.com/c/en/us/td/docs/switches/blades/3040/software/release/12-2_44_se/configuration/guide/swhsrp.html#wp1083927
