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QUESTION NO: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#i
ntracking
QUESTION NO: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:
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.
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 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: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
Explanation:
QUESTION NO:27
Refer to the exhibit.
What triggered the first SPF recalculation?
A. changes in a router LSA, subnet LSA, and external LSA
B. changes in a router LSA, summary network LSA, and external LSA
C. changes in a router LSA, summary network LSA, and summary ASBR LSA
D. changes in a router LSA, summary ASBR LSA, and external LSA
Answer: B
Explanation:
OSPFv2
Is built around links, and any IP prefix change in an area will trigger a full SPF. It advertises IP
information in Router and Network LSAs. The routers thus, advertise both the IP prefix information
(or the connected subnet information) and topology information in the same LSAs. This implies
that if an IP address attached to an interface changes, OSPF routers would have to originate a
Router LSA or a Network LSA, which btw also carries the topology information. This would trigger
a full SPF on all routers in that area, since the same LSAs are flooded to convey topological
change information. This can be an issue with an access router or the one sitting at the edge,
since many stub links can change regularly.
Only changes in interarea, external and NSSA routes result in partial SPF calculation (since type
3, 4, 5 and 7 LSAs only advertise IP prefix information) and thus IS-IS
400-101 PDF Dumps400-101 Practice Test400-101 Study Guide
QUESTION NO:30
What is the flooding scope of an OSPFv3 LSA, if the value of the S2 bit is set to 1 and the S1 bit is
set to 0?
A. link local
B. area wide
C. AS wide
D. reserved
Answer: C
Explanation:
The Type 1 router LSA is now link local and the Type 2 Network LSA is AS Wide
S2 and S1 indicate the LSA\’s flooding scope. Table 9-1 shows the possible values of these two
bits and the associated flooding scopes.
Table 9-1 S bits in the OSPFv3 LSA Link State Type field and their associated flooding scopes
LSA Function Code, the last 13 bits of the LS Type field, corresponds to the OSPFv2 Type field.
Table 9-2 shows the common LSA types used by OSPFv3 and the values of their corresponding
LS Types. If you decode the hex values, you will see that the default U bit of all of them is 0. The S
bits of all LSAs except two indicate area scope. Of the remaining two, AS External LSAs have an
AS flooding scope and Link LSAs have a linklocal flooding scope. Most of the OSPFv3 LSAs have
functional counterparts in OSPFv2; these OSPFv2 LSAs and their types are also shown in Table
9-2.
Table 9-2 OSPFv3 LSA types and their OSPFv2 counterparts
Reference
http://www.networkworld.com/subnets/cisco/050107-ch9-ospfv3.html?page=1
QUESTION NO:32
Which two tunneling techniques support IPv6 multicasting? (Choose two.)
A. 6to4
B. 6over4
C. ISATAP
D. 6PE
E. GRE
Answer: B,E
Explanation:
When IPv6 multicast is supported (over a 6to4 tunnel), an IPv6 multicast routing protocol must be
used
Restrictions for Implementing IPv6 Multicast
IPv6 multicast for Cisco IOS software uses MLD version 2. This version of MLD is fully backward-
compatible with MLD version 1 (described in RFC 2710). Hosts that support only MLD version 1
will interoperate with a router running MLD version 2. Mixed LANs with both MLD version 1 and
MLD version 2 hosts are likewise supported.
IPv6 multicast is supported only over IPv4 tunnels in Cisco IOS Release 12.3(2)T, Cisco IOS
Release 12.2
(18)S, and Cisco IOS Release 12.0(26)S.
When the bidirectional (bidir) range is used in a network, all routers in that network must be able to
understand the bidirectional range in the bootstrap message (BSM).
IPv6 multicast routing is disabled by default when the ipv6 unicast-routing command is configured.
On Cisco Catalyst 6500 and Cisco 7600 series routers, the ipv6 multicast-routing also must be
enabled in order to use IPv6 unicast routing
Reference http://www.cisco.com/web/about/ac123/ac147/ac174/ac197/
about_cisco_ipj_archive_article09186a00800c830a.html
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-multicast.html
https://supportforums.cisco.com/thread/183386
QUESTION NO:36
For which routes does LDP advertise a label binding?
A. all routes in the routing table
B. only the IGP and BGP routes in the routing table
C. only the BGP routes in the routing table
D. only the IGP routes in the routing table
Answer: D
Explanation:
QUESTION NO:42
Which type of domains is interconnected using Multicast Source Discovery Protocol?
A. PIM-SM
B. PIM-DM
C. PIM-SSM
D. DVMRP
Answer: A
Explanation: Multicast Source Discovery Protocol (MSDP) is a Protocol Independent Multicast
(PIM) family multicast routing protocol defined by Experimental RFC 3618. MSDP interconnects
multiple IPv4 PIM Sparse-Mode (PIM-SM) domains which enables PIM-SM to have Rendezvous
Point (RP) redundancy and inter-domain multicasting.
Reference
http://en.wikipedia.org/wiki/Multicast_Source_Discovery_Protocol
QUESTION NO:44
How is RPF used in multicast routing?
A. to prevent multicast packets from looping
B. to prevent PIM packets from looping
C. to instruct PIM where to send a (*, G) or (S, G) join message
D. to prevent multicast packets from looping and to instruct PIM where to send a (*, G) or (S, G)
join message
Answer: D
Explanation:
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