Question 1.
Which two commands are required to enable multicast on a router, knowing that the receivers only support IGMPv2? (Choose two.)

A. ip pim rp-address
B. ip pim ssm
C. ip pim sparse-mode
D. ip pim passive

Answer: A, C

Explanation: 
Sparse mode logic (pull mode) is the opposite of Dense mode logic (push mode), in Dense mode it is supposed that in every network there is someone who is requesting the multicast traffic so PIM-DM routers begin by flooding the multicast traffic out of all their interfaces except those from where a prune message is received to eliminate the “leaf” from the multicasting tree (SPT), the Source-Based Tree (S, G); as opposed to Sparse mode that send the traffic only if someone explicitly requested it. Not like Dense mode, which build a separated source-based tree (S, G) between the source and the requester of the traffic, Sparse mode mechanism is based on a fixed point in the network named Rendez-Vous point. All sources will have to register with the RP to which they send their traffic and thereby build a source-based tree (S, G) between them and the RP (not with the final multicast receiver like in PIM-DM) and all PIM-SM routers, “whatever” multicast traffic they are requesting, have to register with the RP and build a shared-tree (*. G)

Reference
http://tools.ietf.org/html/rfc2236
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00800b0871.shtml
http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094821.shtml#sparsemode

Question 2.
A branch router is configured with an egress QoS policy that was designed for a total number of 10 concurrent VOIP calls. Due to expansion, 15 VOIP calls are now running over the link, but after the 14th call was established, all calls were affected and the voice quality was dramatically degraded. 

Assuming that there is enough bandwidth on the link for all of this traffic, which part of the QoS configuration should be updated due to the new traffic profile?

A. Increase the shaping rate for the priority queue.
B. Remove the policer applied on the priority queue.
C. Remove the shaper applied on the priority queue.
D. Increase the policing rate for the priority queue.

Answer: D

Explanation: 

Question 3.
A new backup connection is being deployed on a remote site router. The stability of the connection has been a concern. In order to provide more information to EIGRP regarding this interface, you wish to incorporate the "reliability" cost metric in the EIGRP calculation with the command metric weights 1 0 1 0 1.

What impact will this modification on the remote site router have for other existing EIGRP neighborships from the same EIGRP domain?

A. Existing neighbors will immediately begin using the new metric.
B. Existing neighbors will use the new metric after clearing the EIGRP neighbors.
C. Existing neighbors will resync, maintaining the neighbor relationship.
D. All existing neighbor relationships will go down.

Answer: D

Explanation: 

Question 4.
Refer to the exhibit.
R1 has an EBGP session to ISP 1 and an EBGP session to ISP 2. R1 receives the same prefixes through both links. 

Which configuration should be applied so that the link between R1 and ISP 2 will be preferred for outgoing traffic (R1 to ISP 2)? 

A. Increase local preference on R1 for received routes
B. Decrease local preference on R1 for received routes
C. Increase MED on ISP 2 for received routes
D. Decrease MED on ISP 2 for received routes

Answer: A

Explanation:  
Explanation
Local preference is an indication to the AS about which path has preference to exit the AS in order to reach a certain network. A path with higher local preference is preferred more. The default value of preference is 100.

Reference
http://www.cisco.com/en/US/tech/tk872/technologies_configuration_example09186a0080b82d1f.shtml? referring_site=smartnavRD

Question 5.
Refer to the exhibit.
A small enterprise connects its office to two ISPs, using separate T1 links. A static route is used for the default route, pointing to both interfaces with a different administrative distance, so that one of the default routes is preferred. Recently the primary link has been upgraded to a new 10 Mb/s Ethernet link. After a few weeks, they experienced a failure. The link did not pass traffic, but the primary static route remained active. They lost their Internet connectivity, even though the backup link was operating.

Which two possible solutions can be implemented to avoid this situation in the future? (Choose two.)

A. Implement HSRP link tracking on the branch router R1.
B. Use a track object with an IP SLA probe for the static route on R1.
C. Track the link state of the Ethernet link using a track object on R1.
D. Use a routing protocol between R1 and the upstream ISP.

Answer: B, D

Explanation: 
Interface Tracking
Interface tracking allows you to specify another interface on the router for the HSRP process to
monitor in order to alter the HSRP priority for a given group. If the specified interface's line protocol goes down, the HSRP priority of this router is reduced, allowing another HSRP router with higher priority can become active (if it has preemption enabled). To configure HSRP interface tracking, use the standby [group] track interface [priority] command. When multiple tracked interfaces are down, the priority is reduced by a cumulative amount. If you explicitly set the decrement value, then the value is decreased by that amount if that interface is down, and decrements are cumulative. If you do not set an explicit decrement value, then the value is decreased by 10 for each interface that goes down, and decrements are cumulative. The following example uses the following configuration, with the default decrement value of 10. 
Note: When an HSRP group number is not specified, the default group number is group 0. 
interface ethernet0
ip address 10.1.1.1 255.255.255.0
standby ip 10.1.1.3
standby priority 110
standby track serial0
standby track serial1
The HSRP behavior with this configuration is:
0 interfaces down = no decrease (priority is 110)
1 interface down = decrease by 10 (priority becomes100)
2 interfaces down = decrease by 10 (priority becomes 90)

Reference
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a91.shtml#intracking

Question 6.
Why would a rogue host that is running a DHCP server on a campus LAN network present a security risk?

A. It may allocate IP addresses from an unknown subnet to the users.
B. All multicast traffic can be sniffed by using the DHCP multicast capabilities.
C. The CPU utilization of the first hop router can be overloaded by exploiting DHCP relay open 
    ports.
D. A potential man-in-the-middle attack can be used against the clients.

Answer: D

Explanation: 

Question 7.
Which statement is true about TCN propagation?

A. The originator of the TCN immediately floods this information through the network.
B. The TCN propagation is a two step process.
C. A TCN is generated and sent to the root bridge.
D. The root bridge must flood this information throughout the network.

Answer: C

Explanation: 
Explanation
New Topology Change Mechanisms
When an 802.1D bridge detects a topology change, it uses a reliable mechanism to first notify the root bridge.
This is shown in this diagram:
C:\Documents and Settings\user-nwz\Desktop\1.JPG
Once the root bridge is aware of a change in the topology of the network, it sets the TC flag on the BPDUs it sends out, which are then relayed to all the bridges in the network. When a bridge receives a BPDU with the TC flag bit set, it reduces its bridging-table aging time to forward delay seconds. This ensures a relatively quick flush of stale information. Refer to Understanding Spanning-Tree Protocol Topology Changes for more information on this process. This topology change mechanism is deeply remodeled in RSTP. Both the detection of a topology change and its propagation through the network evolve.
Topology Change Detection
In RSTP, only non-edge ports that move to the forwarding state cause a topology change. This means that a loss of connectivity is not considered as a topology change any more, contrary to 802.1D (that is, a port that moves to blocking no longer generates a TC). When a RSTP bridge detects a topology change, these occur: 
It starts the TC While timer with a value equal to twice the hello-time for all its non-edge designated ports and its root port, if necessary.
It flushes the MAC addresses associated with all these ports.
Note: As long as the TC While timer runs on a port, the BPDUs sent out of that port have the TC
bit set. BPDUs are also sent on the root port while the timer is active.
Topology Change Propagation
When a bridge receives a BPDU with the TC bit set from a neighbor, these occur:
It clears the MAC addresses learned on all its ports, except the one that receives the topology change. It starts the TC While timer and sends BPDUs with TC set on all its designated ports and root port (RSTP no longer uses the specific TCN BPDU, unless a legacy bridge needs to be notified). This way, the TCN floods very quickly across the whole network. The TC propagation is now a one step process. In fact, the initiator of the topology change floods this information throughout the network, as opposed to 802.1D where only the root did. This mechanism is much faster than the 802.1D equivalent. There is no need to wait for the root bridge to be notified and then maintain the topology change state for the whole network for  seconds. C:\Documents and Settings\user-nwz\Desktop\1.JPG
In just a few seconds, or a small multiple of hello-times, most of the entries in the CAM tables of the entire network (VLAN) flush. This approach results in potentially more temporary flooding, but on the other hand it clears potential stale information that prevents rapid connectivity restitution.

Reference
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml

Question 8.
Which statement is true about loop guard?

A. Loop guard only operates on interfaces that are considered point-to-point by the spanning tree.
B. Loop guard only operates on root ports.
C. Loop guard only operates on designated ports.
D. Loop guard only operates on edge ports.

Answer: A

Explanation: 
Explanation
Understanding How Loop Guard Works
Unidirectional link failures may cause a root port or alternate port to become designated as root if BPDUs are absent. Some software failures may introduce temporary loops in the network. Loop guard checks if a root port or an alternate root port receives BPDUs. If the port is receiving BPDUs, loop guard puts the port into an inconsistent state until it starts receiving BPDUs again. Loop guard isolates the failure and lets spanning tree converge to a stable topology without the failed link or bridge. You can enable loop guard per port with the set spantree guard loop command. Note When you are in MST mode, you can set all the ports on a switch with the set spantree global-defaults loop-guard command. When you enable loop guard, it is automatically applied to all of the active instances or VLANs to which that port belongs. When you disable loop guard, it is disabled for the specified ports. Disabling loop guard moves all loop-inconsistent ports to the listening state. If you enable loop guard on a channel and the first link becomes unidirectional, loop guard blocks the entire channel until the affected port is removed from the channel. Figure 8-6 shows loop guard in a triangle switch configuration.
Figure 8-6 Triangle Switch Configuration with Loop Guard
C:\Documents and Settings\user-nwz\Desktop\1.JPG
Figure 8-6 illustrates the following configuration:
Switches A and B are distribution switches.
Switch C is an access switch.
Loop guard is enabled on ports 3/1 and 3/2 on Switches A, B, and C.
Use loop guard only in topologies where there are blocked ports. Topologies that have no blocked ports, which are loop free, do not need to enable this feature. Enabling loop guard on a root switch has no effect but provides protection when a root switch becomes a nonroot switch.
Follow these guidelines when using loop guard:
Do not enable loop guard on PortFast-enabled or dynamic VLAN ports.
Do not enable PortFast on loop guard-enabled ports.
Do not enable loop guard if root guard is enabled.
Do not enable loop guard on ports that are connected to a shared link.
Note We recommend that you enable loop guard on root ports and alternate root ports on access
switches. Loop guard interacts with other features as follows:
Loop guard does not affect the functionality of UplinkFast or BackboneFast.
Root guard forces a port to always be designated as the root port. Loop guard is effective only if the port is a root port or an alternate port. Do not enable loop guard and root guard on a port at the same time. PortFast transitions a port into a forwarding state immediately when a link is established. Because a PortFast-enabled port will not be a root port or alternate port, loop guard and PortFast cannot be configured on the same port. Assigning dynamic VLAN membership for the port requires that the port is PortFast enabled. Do not configure a loop guard-enabled port with dynamic VLAN membership.

If your network has a type-inconsistent port or a PVID-inconsistent port, all BPDUs are dropped until the misconfiguration is corrected. The port transitions out of the inconsistent state after the message age expires. Loop guard ignores the message age expiration on type-inconsistent ports and PVID-inconsistent ports. If the port is already blocked by loop guard, misconfigured BPDUs that are received on the port make loop guard recover, but the port is moved into the typeinconsistent state or PVID-inconsistent state. In high-availability switch configurations, if a port is put into the blocked state by loop guard, it remains blocked even after a switchover to the redundant supervisor engine. The newly activated supervisor engine recovers the port only after receiving a BPDU on that port. Loop guard uses the ports known to spanning tree. Loop guard can take advantage of logical ports provided by the Port Aggregation Protocol (PAgP). However, to form a channel, all the physical ports grouped in the channel must have compatible configurations. PAgP enforces uniform configurations of root guard or loop guard on all the physical ports to form a channel. 
These caveats apply to loop guard:
–Spanning tree always chooses the first operational port in the channel to send the BPDUs. If that link becomes unidirectional, loop guard blocks the channel, even if other links in the channel are functioning properly.
–If a set of ports that are already blocked by loop guard are grouped together to form a channel, spanning tree loses all the state information for those ports and the new channel port may obtain the forwarding state with a designated role.
–If a channel is blocked by loop guard and the channel breaks, spanning tree loses all the state information.
The individual physical ports may obtain the forwarding state with the designated role, even if one or more of the links that formed the channel are unidirectional.
You can enable UniDirectional Link Detection (UDLD) to help isolate the link failure. A loop may occur until
UDLD detects the failure, but loop guard will not be able to detect it.
Loop guard has no effect on a disabled spanning tree instance or a VLAN.

Reference
http://www.cisco.com/en/US/docs/switches/lan/catalyst4000/8.2glx/configuration/guide/stp_enha.
html#wp1048163

Question 9.
Which two are effects of connecting a network segment that is running 802.1D to a network segment that is running 802.1w? (Choose two.)

A. The entire network switches to 802.1D and generates BPDUs to determine root bridge status.
B. A migration delay of three seconds occurs when the port that is connected to the 802.1D 
    Bridge comes up.
C. The entire network reconverges and a unique root bridge for the 802.1D segment, and a root 
    bridge for the 802.1w segment, is chosen.
D. The first hop 802.1w switch that is connected to the 802.1D runs entirely in 802.1D  
    Compatibility mode and converts the BPDUs to either 802.1D or 802.1w BPDUs to the 802.1D 
    or 802.1w segments of the network.
E. Classic 802.1D timers, such as forward delay and max-age, will only be used as a backup, and  
    will not be necessary if point-to-point links and edge ports are properly identified and set by the  
    administrator.

Answer: B, E

Explanation: 
Explanation
Each port maintains a variable that defines the protocol to run on the corresponding segment. A migration delay timer of three seconds also starts when the port comes up. When this timer runs, the current STP or RSTP mode associated to the port is locked. As soon as the migration delay expires, the port adapts to the mode that corresponds to the next BPDU it receives. If the port changes its mode of operation as a result of a BPDU received, the migration delay restarts. 802.1D works by the concept that the protocol had to wait for the network to converge before it transitioned a port into the forwarding state. With Rapid Spanning Tree it does not have to rely on any timers, the only variables that that it relies on is edge ports and link types.
Any uplink port that has an alternate port to the root can be directly placed into the forwarding state (This is the Rapid convergence that you speak of "restored quickly when RSTP is already in use?"). This is what happened when you disconnected the primary look; the port that was ALT, moved to FWD immediately, but the switch also still needs to create a BDU with the TC bit set to notify the rest of the network that a topology has occurred and all non-edge designated ports will transition to BLK, LRN, and then FWD to ensure there are no loops in the rest of the network. This is why if you have a host on a switchport, and you know for a fact that it is only one host, enable portfast to configure the port as an edgeport so that it does not have to transition to all the STP states.

Reference
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml

Question 10.
Which command is used to enable EtherChannel hashing for Layer 3 IP and Layer 4 port-based CEF?

A. mpls ip cef
B. port-channel ip cef
C. mpls ip port-channel cef
D. port-channel load balance
E. mpls ip load-balance
F. ip cef EtherChannel channel-id XOR L4
G. ip cef connection exchange

Answer: D
	
Explanation: 

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