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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:11
When you are troubleshooting duplex mismatches, which two errors are typically seen on the full-
duplex end? (Choose two.)
A. runts
B. FCS errors
C. interface resets
D. late collisions
Answer: A,B
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:
QUESTION NO: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 NO: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
Explanation:
Latest 400-101 Dumps400-101 PDF Dumps400-101 Exam Questions
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:43
Which two multicast address ranges are assigned as source-specific multicast destination
addresses and are reserved for use by source-specific applications and protocols? (Choose two.)
A. 232.0.0.0/8
B. 239.0.0.0/8
C. 232.0.0.0/4
D. FF3x::/32
E. FF2x::/32
F. FF3x::/16
Answer: A,D
Explanation: Source-specific multicast (SSM) is a method of delivering multicast packets in which
the only packets that are delivered to a receiver are those originating from a specific source
address requested by the receiver. By so limiting the source, SSM reduces demands on the
network and improves security.
SSM requires that the receiver specify the source address and explicitly excludes the use of the (*,
G) join for all multicast groups in RFC 3376, which is possible only in IPv4’s IGMPv3 and IPv6’s
MLDv2.
Source-specific multicast is best understood in contrast to any-source multicast (ASM). In the
ASM service model a receiver expresses interest in traffic to a multicast address. The multicast
network must
1. discover all multicast sources sending to that address, and
2. route data from all sources to all interested receivers.
This behavior is particularly well suited to groupware applications where
1. all participants in the group want to be aware of all other participants, and
2. the list of participants is not known in advance.
The source discovery burden on the network can become significant when the number of sources
is large.
In the SSM service model, in addition to the receiver expressing interest in traffic to a multicast
address, the receiver expresses interest in receiving traffic from only one specific source sending
to that multicast address.
This relieves the network of discovering many multicast sources and reduces the amount of
multicast routing information that the network must maintain.
SSM requires support in last-hop routers and in the receiver’s operating system. SSM support is
not required in other network components, including routers and even the sending host. Interest in
multicast traffic from a specific source is conveyed from hosts to routers using IGMPv3 as
specified in RFC 4607.
SSM destination addresses must be in the ranges 232.0.0.0/8 for IPv4 or FF3x::/96 for IPv6.
Reference
http://en.wikipedia.org/wiki/Source-specific_multicast
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:
QUESTION NO:47
Apart from interdomain multicast routing, what else is MSDP used for?
A. Source Specific Multicast and IGMPv2
B. Announcing multicast sources to BGP speakers
C. Anycast RP
D. Intradomain multicast routing
Answer: C
Explanation:
Reference
http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/
guide/1cfmsdp_ps1835_TSD_Products_Configuration_Guide_Chapter.html
QUESTION NO:49
Refer to the exhibit.
Which IGMPv2 message is displayed in the output of the packet capture?
A. General Query
B. Membership Report
C. Membership Query
D. Membership Delay
Answer: B
Explanation:
Reference
http://wiki.wireshark.org/IGMP
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