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QUESTION NO: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
QUESTION NO: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
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 type-
inconsistent 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:
QUESTION NO: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:
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 NO: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:
QUESTION NO:13
Which two statements are true about traffic shaping? (Choose two.)
A. Out-of-profile packets are queued.
B. It causes TCP retransmits.
C. Marking/remarking is not supported.
D. It does not respond to BECN and ForeSight Messages.
E. It uses a single/two-bucket mechanism for metering.
Answer: A,C
Explanation:
400-101 VCE Dumps400-101 Practice Test400-101 Study Guide
QUESTION NO:17
Which three combinations are valid LACP configurations that will set up a channel? (Choose
three.)
A. On/On
B. On/Auto
C. Passive/Active
D. Desirable/Auto
E. Active/Active
F. Desirable/Desirable
Answer: A,C,E
Explanation:
QUESTION NO:22
Refer to the exhibit.
Which path is selected as best path?
A. path 1, because it is learned from IGP B.
path 1, because the metric is the lowest C.
path 2, because it is external
D. path 2, because it has the higher router ID
Answer: B
Explanation:
QUESTION NO:24
Refer to the exhibit.
R1 is not learning about the 172.16.10.0 subnet from the BGP neighbor R2 (209.165.202.130).
What can be done so that R1 will learn about this network?
A. Disable auto-summary on R2.
B. Configure an explicit network command for the 172.16.10.0 subnet on R2.
C. Subnet information cannot be passed between IBGP peers.
D. Disable auto-summary on R1.
Answer: B
Explanation:
By default, BGP does not accept subnets redistributed from IGP. To advertise and carry subnet
routes in BGP, use an explicit network command or the no auto-summary command. If you disable
auto-summarization and have not entered a network command, you will not advertise network
routes for networks with subnet routes unless they contain a summary route.
Reference
http://www.cisco.com/en/US/docs/ios/11_3/np1/command/reference/1rbgp.html
QUESTION NO:29
What is the first thing that happens when IPv6 is enabled on an interface on a host?
A. A router solicitation is sent on that interface.
B. There is a duplicate address detection on the host interface.
C. The link local address is assigned on the host interface.
D. A neighbor redirect message is sent on the host interface.
Answer: B
Explanation:
Duplicate address detection (DAD) is used to verify that an IPv6 home address is unique on the
LAN before assigning the address to a physical interface (for example, QDIO). z/OS
Communications Server responds to other nodes doing DAD for IP addresses assigned to the
interface.
Reference
http://publib.boulder.ibm.com/infocenter/zos/v1r12/index.jsp?topic=/com.ibm.zos.r12.hale001
/ipv6d0021002145.htm
QUESTION NO:35
Which command will define a VRF with name ‘CCIE’ in IPv6?
A. ip vrf CCIE
B. ipv6 vrf CCIE
C. vrf definition CCIE
D. ipv6 vrf definition CCIE
Answer: C
Explanation:
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