Cisco
Exam Name: CCIE Routing and Switching Written Qualification Exam v4.0
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Question:
1
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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
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Answer: A,C
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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
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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.
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Answer: D
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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.
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Answer: D
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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
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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
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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
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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.
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Answer: D
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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:
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:
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 <max age plus forward delay> seconds.
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
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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
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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 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
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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
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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
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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
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|
Question:
11
|
When you are
troubleshooting duplex mismatches, which two errors are typically seen on the
fullduplex end? (Choose two.)
A. runts
B. FCS errors
C. interface resets
D. late collisions
|
Answer: A,B
|
|
Question:
12
|
Which two options are
contained in a VTP subset advertisement? (Choose two.)
A. followers field
B. MD5 digest
C. VLAN information
D. sequence number
|
Answer: C,D
|
Explanation:
Subset Advertisements
When you add, delete, or
change a VLAN in a Catalyst, the server Catalyst where the changes are made
increments the configuration revision and issues a summary advertisement. One
or several subset advertisements follow the summary advertisement. A subset
advertisement contains a list of VLAN information. If there are several VLANs,
more than one subset advertisement can be required in order to advertise all
the VLANs. Subset Advertisement Packet Format
This formatted example
shows that each VLAN information field contains information for a different
VLAN. It is ordered so that lowered-valued ISL VLAN IDs occur first:
Most of the fields in this
packet are easy to understand. These are two clarifications:
Code — The format for this
is 0x02 for subset advertisement. Sequence number — This is the sequence of the
packet in the stream of packets that follow a summary advertisement. The sequence
starts with 1.
Advertisement Requests
A switch needs a VTP
advertisement request in these situations:
The switch has been reset.
The VTP domain name has
been changed.
The switch has received a
VTP summary advertisement with a higher configuration revision than its own.
Upon receipt of an advertisement request, a VTP device sends a summary
advertisement. One or more subset advertisements follow the summary
advertisement. This is an example:
Code—The format for this
is 0x03 for an advertisement request.
Start-Value—This is used
in cases in which there are several subset advertisements. If the first (n)
subset advertisement has been received and the subsequent one (n+1) has not
been received, the Catalyst only requests advertisements from the (n+1)th one.
Reference
http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094c52.shtml
|
Question:
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
|
|
Question:
14
|
Which three options are
features of VTP version 3? (Choose three.)
A. VTPv3 supports 8K
VLANs.
B. VTPv3 supports private
VLAN mapping.
C. VTPv3 allows for domain
discovery.
D. VTPv3 uses a primary
server concept to avoid configuration revision issues.
E. VTPv3 is not compatible
with VTPv1 or VTPv2.
F. VTPv3 has a hidden
password option.
|
Answer: B,D,F
|
Explanation:
Key Benefits of VTP
Version 3 Much work has gone into improving the usability of VTP version 3 in
three major areas:
The new version of VTP
offers better administrative control over which device is allowed to update
other devices' view of the VLAN topology. The chance of unintended and
disruptive changes is significantly reduced, and availability is increased. The
reduced risk of unintended changes will ease the change process and help speed
deployment. Functionality for the VLAN environment has been significantly
expanded. Two enhancements are most beneficial for today's networks:
– In addition to
supporting the earlier ISL VLAN range from 1 to 1001, the new version supports
the whole IEEE 802.1Q VLAN range up to 4095.
– In addition to
supporting the concept of normal VLANs, VTP version 3 can transfer information
regarding Private VLAN (PVLAN) structures.
The third area of major
improvement is support for databases other than VLAN (for example, MST).
Brief Background on VTP
Version 1 and VTP Version 2
VTP version 1 was
developed when only 1k VLANs where available for configuration. A tight
internal coupling of the VLAN implementation, the VLAN pruning feature, and the
VTP function itself offered an efficient means of implementation. It has proved
in the field to reliably support Ethernet, Token Ring, and FDDI networks via
VTP. The use of consistent VLAN naming was a requirement for successful use of
VMPS (Vlan Membership Policy Server). VTP ensures the consistency of VLAN names
across the VTP domain. Most VMPS implementations are likely to be migrated to a
newer, more flexible and feature-rich method. To add support for Token Ring,
VTP version 1 was enhanced and called VTP version 2. Certain other minor
changes and enhancements were also added at this time. The functional base in
VTP version 3 is left unchanged from VTP version 2, so backward compatibility
is built in. It is possible, on a per link basis, to automatically discover and
support VTP version 2 devices. VTP version 3 adds a number of enhancements to
VTP version 1 and VTP version 2:
Support for a structured
and secure VLAN environment (Private VLAN, or PVLAN)
Support for up to 4k VLANs
Feature enhancement beyond support for a single database or VTP instance
Protection from unintended database overrides during insertion of new switches
Option of clear text or hidden password protection Configuration option on a
per port base instead of only a global scheme Optimized resource handling and
more efficient transfer of information These new requirements made a new code
foundation necessary. The design goal was to make VTP version 3 a versatile
vehicle. This was not only for the task of transferring a VLAN DB but also for
transferring other databases-for example, the MST database.
Reference
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/solution_guide_c78_508010.html
|
Question:
15
|
Which three options are
considered in the spanning-tree decision process? (Choose three.)
A. lowest root bridge ID
B. lowest path cost to
root bridge
C. lowest sender bridge ID
D. highest port ID
E. highest root bridge ID
F. highest path cost to
root bridge
|
Answer: A,B,C
|
Explanation:
Configuration bridge
protocol data units (BPDUs) are sent between switches for each port. Switches
use s four step process to save a copy of the best BPDU seen on every port.
When a port receives a better BPDU, it stops sending them. If the BPDUs stop
arriving for 20 seconds (default), it begins sending them again.
Step 1 Lowest Root Bridge
ID (BID)
Step 2 Lowest Path Cost to
Root Bridge
Step 3 Lowest Sender BID
Step 4 Lowest Port ID
Reference
Cisco General Networking
Theory Quick Reference Sheets
|
Question:
16
|
In 802.1s, how is the VLAN
to instance mapping represented in the BPDU?
A. The VLAN to instance
mapping is a normal 16-byte field in the MST BPDU.
B. The VLAN to instance
mapping is a normal 12-byte field in the MST BPDU.
C. The VLAN to instance
mapping is a 16-byte MD5 signature field in the MST BPDU.
D. The VLAN to instance
mapping is a 12-byte MD5 signature field in the MST BPDU.
|
Answer: C
|
Explanation:
MST Configuration and MST
Region Each switch running MST in the network has a single MST configuration
that consists of these three attributes:
1. An alphanumeric
configuration name (32 bytes)
2. A configuration
revision number (two bytes)
3. A 4096-element table
that associates each of the potential 4096 VLANs supported on the chassis to a
given instance.
In order to be part of a
common MST region, a group of switches must share the same configuration
attributes. It is up to the network administrator to properly propagate the
configuration throughout the region. Currently, this step is only possible by
the means of the command line interface (CLI) or through Simple Network
Management Protocol (SNMP). Other methods can be envisioned, as the IEEE
specification does not explicitly mention how to accomplish that step. Note: If
for any reason two switches differ on one or more configuration attribute, the
switches are part of different regions. For more information refer to the
Region Boundary section of this document.
Region Boundary
In order to ensure
consistent VLAN-to-instance mapping, it is necessary for the protocol to be
able to exactly identify the boundaries of the regions. For that purpose, the
characteristics of the region are included in the BPDUs. The exact
VLANs-to-instance mapping is not propagated in the BPDU, because the switches
only need to know whether they are in the same region as a neighbor. Therefore,
only a digest of the VLANs-toinstance mapping table is sent, along with the
revision number and the name. Once a switch receives a BPDU, the switch
extracts the digest (a numerical value derived from the VLAN-to-instance
mapping table through a mathematical function) and compares this digest with
its own computed digest. If the digests differ, the port on which the BPDU was
received is at the boundary of a region. In generic terms, a port is at the
boundary of a region if the designated bridge on its segment is in a different
region or if it receives legacy 802.1d BPDUs. In this diagram, the port on B1
is at the boundary of region A, whereas the ports on B2 and B3 are internal to
region B:
MST Instances
According to the IEEE
802.1s specification, an MST bridge must be able to handle at least these two
instances:
One Internal Spanning Tree
(IST)
One or more Multiple
Spanning Tree Instance(s) (MSTIs)
The terminology continues
to evolve, as 802.1s is actually in a pre-standard phase. It is likely these
names will change in the final release of 802.1s. The Cisco implementation
supports 16 instances: one IST (instance 0) and 15 MSTIs. show vtp status Cisco
switches "show vtp status" Field Descriptions has a MD5 digest field
that is a 16-byte checksum of the
VTP configuration as shown
below
Router# show vtp status
VTP Version: 3 (capable)
Configuration Revision: 1
Maximum VLANs supported
locally: 1005
Number of existing VLANs:
37
VTP Operating Mode: Server
VTP Domain Name:
[smartports]
VTP Pruning Mode: Disabled
VTP V2 Mode: Enabled
VTP Traps Generation:
Disabled
MD5 digest : 0x26 0xEE
0x0D 0x84 0x73 0x0E 0x1B 0x69
Configuration last
modified by 172.20.52.19 at 7-25-08 14:33:43
Local updater ID is
172.20.52.19 on interface Gi5/2 (first layer3 interface fou)
VTP version running: 2
Reference
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml
http://www.cisco.com/en/US/docs/ios-xml/ios/lanswitch/command/lsw-cr-book.pdf
|
Question:
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
|
|
Question:
18
|
Refer to the exhibit.
Which statement is correct
about the prefix 160.0.0.0/8?
A. The prefix has
encountered a routing loop.
B. The prefix is an
aggregate with an as-set.
C. The prefix has been
aggregated twice, once in AS 100 and once in AS 200.
D. None of these
statements is true.
|
Answer: B
|
|
Question:
19
|
Which two options does
Cisco PfR use to control the entrance link selection with inbound optimization?
(Choose two.)
A. Prepend extra AS hops
to the BGP prefix.
B. Advertise more specific
BGP prefixes (longer mask).
C. Add (prepend) one or
more communities to the prefix that is advertised by BGP.
D. Have BGP dampen the
prefix.
|
Answer: A,C
|
Explanation: PfR Entrance
Link Selection Control Techniques The PfR BGP inbound optimization feature
introduced the ability to influence inbound traffic. A network advertises
reachabi ity of its inside prefixes to the Internet using eBGP advertisements
to its ISPs. If the same prefix is advertised to more than one ISP, then the
network is multihoming. PfR BGP inbound optimization works best with multihomed
networks, but it can also be used with a network that has multiple connections
to the same ISP. To implement BGP inbound optimization, PfR manipulates eBGP
advertisements to influence the best entrance selection for traffic bound for
inside prefixes. The benefit of implementing the best entrance selection is
limited to a network that has more than one ISP connection. To enforce an
entrance link selection, PfR offers the following methods:
BGP Autonomous System
Number Prepend When an entrance link goes out-of-policy (OOP) due to delay, or
in images prior to Cisco IOS Releases 15.2(1) T1 and 15.1(2)S, and PfR selects
a best entrance for an inside prefix, extra autonomous system hops are
prepended one at a time (up to a maximum of six) to the inside prefix BGP
advertisement over the other entrances. In Cisco IOS Releases 15.2(1)T1,
15.1(2)S, and later releases, when an entrance link goes out-of policy (OOP)
due to unreachable or loss reasons, and PfR selects a best entrance for an inside
prefix, six extra autonomous system hops are prepended immediately to the
inside prefix BGP advertisement over the other entrances. The extra autonomous
system hops on the other entrances increase the probability that the best
entrance will be used for the inside prefix. When the entrance link is OOP due
to unreachable or loss reasons, six extra autonomous system hops are added
immediately to allow the software to quickly move the traffic away from the old
entrance link. This is the default method PfR uses to control an inside prefix,
and no user configuration is required.
BGP Autonomous System
Number Community Prepend When an entrance link goes out-of-policy (OOP) due to
delay, or in images prior to Cisco IOS Releases 15.2 (1)T1 and 15.1(2)S, and
PfR selects a best entrance for an inside prefix, a BGP prepend community is
attached one at a time (up to a maximum of six) to the inside prefix BGP
advertisement from the network to another autonomous system such as an ISP. In
Cisco IOS Releases 15.2(1)T1, 15.1(2)S, and later releases, when an entrance
link goes out-of-policy (OOP) due to unreachable or loss reasons, and PfR
selects a best entrance for an inside prefix, six BGP prepend communities are
attached to the inside prefix BGP advertisement. The BGP prepend community will
increase the number of autonomous system hops in the advertisement of the
inside prefix from the ISP to its peers. Autonomous system prepend BGP
community is the preferred method to be used for PfR BGP inbound optimization
because there is no risk of the local ISP filtering the extra autonomous system
hops. There are some issues, for example, not all ISPs support the BGP prepend
community, ISP policies may ignore or modify the autonomous system hops, and a
transit ISP may filter the autonomous system path. If you use this method of
inbound optimization and a change is made to an autonomous system, you must
issue an outbound reconfiguration using the "clear ip bgp" command.
Reference
http://www.cisco.com/en/US/docs/ios-xml/ios/pfr/configuration/15-2s/pfr-bgp-inbound.html#GUIDF8A59E24-1D59-4924-827D-B23B43D9A8E0
http://www.cisco.com/en/US/products/ps8787/products_ios_protocol_option_home.html
|
Question:
20
|
Refer to the exhibit.
What is the potential
issue with this configuration?
A. There is no potential
issue; OSPF will work fine in any condition.
B. Sub-optimal routing may
occur since there is no area 1 adjacency between the ABRs.
C. This is a wrong OSPF
configuration because all routers must be in area 0 only.
D. This is a wrong OSPF
configuration because /30 requires 0.0.0.3 wild card.
|
Answer: B
|
|
Question:
21
|
Refer to the exhibit.
A packet from RTD with
destination RTG, is reaching RTB. What is the path this packet will take from
RTB to reach RTG?
A. RTB - RTA - RTG
B. RTB - RTD - RTC - RTA -
RTG
C. RTB - RTF - RTE - RTA -
RTG
D. RTB will not be able to
reach RTG since the OSPF configuration is wrong.
|
Answer: C
|
|
Question:
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
|
|
Question:
23
|
What action will a BGP
route reflector take when it receives a prefix marked with the community
attribute NO ADVERTISE from a client peer?
A. It will advertise the
prefix to all other client peers and non-client peers.
B. It will not advertise
the prefix to EBGP peers.
C. It will only advertise
the prefix to all other IBGP peers.
D. It will not advertise
the prefix to any peers.
|
Answer: D
|
|
Question:
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:
25
|
Refer to the exhibit.
After a link flap in the
network, which two EIGRP neighbors will not be queried for alternative paths?
(Choose two.)
A. 192.168.1.1
B. 192.168.3.7
C. 192.168.3.8
D. 192.168.3.6
E. 192.168.2.1
F. 192.168.3.9
|
Answer: B,C
|
Explanation:
Both 192.168.3.7 &
192.168.3.8 are in an EIGRP Stub area
The Enhanced Interior
Gateway Routing Protocol (EIGRP) Stub Routing feature improves network
stability, reduces resource utilization, and simplifies stub router
configuration. Stub routing is commonly used in a hub and spoke network
topology. In a hub and spoke network, one or more end (stub) networks are
connected to a remote router (the spoke) that is connected to one or more
distribution routers (the hub). The remote router is adjacent only to one or
more distribution routers. The only route for IP traffic to follow into the
remote router is through a distribution router. This type of configuration is
commonly used in WAN topologies where the distribution router is directly
connected to a WAN. The distribution router can be connected to many more
remote routers. Often, the distribution router will be connected to 100 or more
remote routers. In a hub and spoke topology, the remote router must forward all
nonlocal traffic to a distribution router, so it becomes unnecessary for the
remote router to hold a complete routing table. Generally, the distribution
router need not send anything more than a default route to the remote router.
When using the EIGRP Stub Routing feature, you need to configure the
distribution and remote routers to use EIGRP, and to configure only the remote
router as a stub. Only specified routes are propagated from the remote (stub)
router. The router responds to queries for summaries, connected routes,
redistributed static routes, external routes, and internal routes with the
message "inaccessible." A router that is configured as a stub will
send a special peer information packet to all neighboring routers to report its
status as a stub router. Any neighbor that receives a packet informing it of
the stub status will not query the stub router for any routes, a d a router
that has a stub peer will not query that peer. The stub router will depend on
the distribution router to send the proper updates to all peers.
Reference
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/eigrpstb.html#wp1021949
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