Free Download Cisco 350-001 VCE Test Engine Full Version Now (141-150)
QUESTION 141
In order to configure two routers as anycast RPs, which of these requirements, at a minimum,
must be satisfied?
A. Multicast Source Discovery Protocol mesh-groups must be configured between the two anycast
RPs.
B. The RPs must be within the same IGP domain.
C. Multicast Source Discovery Protocol must be configured between the two anycast RPs.
D. The two anycast RPs must be IBGP peers.
Answer: C
Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM sparse-mode (SM) domains. MSDP allows multicast sources for a group to be known to all rendezvous point(s) (RPs) in different domains. Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains. An RP runs MSDP over TCP to discover multicast sources in other domains. An RP in a PIM-SM domain has an MSDP peering relationship with MSDP-enabled routers in another domain. The peering relationship occurs over a TCP connection, where primarily a list of sources sending to multicast groups is exchanged. The TCP connections between RPs are achieved by the underlying routing system. The receiving RP uses the source lists to establish a source path. The purpose of this topology is to have domains discover multicast sources in other domains. If the multicast sources are of interest to a domain that has
receivers, multicast data is delivered over the normal, source-tree building mechanism in PIM-SM. MSDP is also used to announce sources sending to a group. These announcements must originate at the domain’s RP.
MSDP depends heavily on (M)BGP for interdomain operation. It is recommended that you run MSDP in RPs in your domain that are RPs for sources sending to global groups to be announced to the internet.
Each MSDP peer receives and forwards the SA message away from the originating RP to achieve “peer- RPF flooding.” The concept of peer-RPF flooding is with respect to forwarding SA messages. The router examines the BGP or MBGP routing table to determine which peer is the next hop toward the originating RP of the SA message. Such a peer is called an “RPF peer” (Reverse-Path Forwarding peer). The router forwards the message to all MSDP peers other than the RPF peer. If the MSDP peer receives the same SA message from a non-RPF peer toward the originating RP, it drops the message. Otherwise, it forwards the message on to all its MSDP peers. When an RP for a domain receives an SA message from an MSDP peer, it determines if it has any group members interested in the group the SA message describes. If the (*,G) entry exists with a nonempty outgoing interface list, the domain is interested in the group, and the RP triggers an (S,G) join toward the source.
QUESTION 142
Which two of these statements correctly describe classic PIM-SM? (Choose two.)
A. The IOS default is for a last-hop router to trigger a switch to the shortest path tree as soon as a new
source is detected on the shared tree.
B. The IOS default is for every one of the routers on the shared tree to trigger a switch to the shortest
path tree as soon as a new source is detected on the shared tree.
C. The default behavior of switching to the shortest path tree as soon as a new source is detected on
the shared tree can be disabled by setting the value in the ip pim spt-threshold command to
“infinity.”
D. The default behavior of switching to the shortest path tree as soon as a new source is detected on
the shared tree can be disabled by setting the value in the ip pim spt-threshold command to
“zero.”
Answer: AC
Explanation:
They are checking you for syntax ip pim spt-threshold command to “infinity” is the right answer.
same source as above:
IP pim spt-threshold [vrf vrf-name] spt-threshold {kbps | infinity} [group-list access-list] To configure when a Protocol Independent Multicast (PIM) leaf router should join the shortest path source tree for the specified group infinity Causes all sources for the specified group to use the shared tree.
http://www.cisco.com/en/US/docs/ios/12_2/ipmulti/command/reference/1rfmult2.html#wp10201
QUESTION 143
In Layer 2 topologies, spanning-tree failures can cause loops in the network. These unblocked
loops can cause network failures because of excessive traffic. Which two Catalyst 6500 features
can be used to limit excessive traffic during spanning-tree loop conditions? (Choose two.)
A. loop guard
B. storm control
C. storm suppression
D. broadcast suppression
E. BPDU guard
Answer: BD
Explanation:
Traffic Storm Control
A traffic storm occurs when packets flood the LAN, creating excessive traffic and degrading network performance. The traffic storm control feature prevents LAN ports from being disrupted by a broadcast, multicast, or unicast traffic storm on physical interfaces. Traffic storm control (also called traffic suppression) monitors incoming traffic levels over a 1-second traffic storm control interval and, during the interval, compares the traffic level with the traffic storm control level that you configure. The traffic storm control level is a percentage of the total available bandwidth of the port. Each port has a single traffic storm control level that is used for all types of traffic (broadcast, multicast, and unicast).
Traffic storm control monitors the level of each traffic type for which you enable traffic storm control in 1-second traffic storm control intervals. Within an interval, when the ingress traffic for which traffic storm control is enabled reaches the traffic storm control level that is configured on the port, traffic storm control drops the traffic until the traffic storm control interval ends.
Broadcast suppression Broadcast suppression prevents the switched ports on a LAN from being disrupted by a broadcast storm on one of the ports. A LAN broadcast storm occurs when the broadcast or multicast packets flood the LAN, creating excessive traffic and degrading the network performance. Errors in the protocol-stack implementation or in the network configuration can cause a broadcast storm.
Broadcast suppression uses filtering that measures the broadcast activity on a LAN over a time period (15264 nsec to ~1 sec) that varies based on the type of line card and speed setting on the port, and compares the measurement with a predefined threshold. If the threshold is reached, further broadcast activity is suppressed for the duration of a specified time period. Broadcast suppression is disabled by default.
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/gui de/storm.html\
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/catos/8.x/configuration/guide/bcasts up.html
QUESTION 144
Why does RSTP have a better convergence time than 802.1D?
A. it is newer
B. it has smaller timers
C. it has less overhead
D. it is not timer-based
Answer: D
Explanation:
RSTP identifies certain links as point to point. When a point-to-point link fails, the alternate link can transition to the forwarding state.
Although STP provides basic loop prevention functionality, it does not provide fast network convergence when there are topology changes. STP’s process to determine network state transitions is slower than RSTP’s because it is timer-based. A device must reinitialize every time a topology change occurs. The device must start in the listening state and transition to the learning state and eventually to a forwarding or blocking state.
When default values are used for the maximum age (20 seconds) and forward delay (15 seconds), it takes 50 seconds for the device to converge. RSTP converges faster because it uses a handshake mechanism based on point-to-point links instead of the timer-based process used by STP. An RSTP domain running switch has the following components:
A root port, which is the “best path” to the root device. A designated port, indicating that the switch is the designated bridge for the other switch connecting to this port.
An alternate port, which provides an alternate root port. A backup port, which provides an alternate designated port. Port assignments change through messages exchanged throughout the domain. An RSTP device generates configuration messages once every hello time interval. If an RSTP device does not receive a configuration message from its neighbor after an interval of three hello times, it determines it has lost connection with that neighbor. When a root port or a designated port fails on a device, the device generates a configuration message with the proposal bit set. Once its neighbor device receives this message, it verifies that this configuration message is better than the one saved for that port and then it starts a synchronizing operation to ensure that all of its ports are in sync with the new information.
Similar waves of proposal agreement handshake messages propagate toward the leaves of the network, restoring the connectivity very quickly after a topology change (in a well-designed network that uses RSTP, network convergence can take as little as 0.5 seconds). If a device does not receive an agreement to a proposal message it has sent, it returns to the original IEEE 802.D convention. RSTP was originally defined in the IEEE 802.1w draft specification and later incorporated into the IEEE 802.1D-2004 specification.
QUESTION 145
Under which two circumstances would an RSTP bridge flush its CAM table? (Choose two.)
A. upon a port state change
B. upon receiving a topology change notification
C. when transitioning from discarding to forwarding
D. when transitioning from forwarding to discarding
E. only when changing from listening to discarding
F. when CAM resources have been completely used up
Answer: BC
Explanation:
First, the goal of RSTP is fast re-convergence. Since ports are assumed to transition to forwarding relatively fast, simply increasing MAC address aging speed is not enough. Thus, when a topology change is detected, RSTP instructs the bridge to flush all MAC address table entries. With Ethernet, this process results in unconstrained flooding until the moment MAC addresses are re-learned. The bridge detecting a topology change sets the TC (Topology Change) bit in all outgoing BPDUs and starts sending BPDUs with the TC bit set upstream through the root port as well. This marking lasts for TCWhile=2xHelloTime seconds and allows the detecting bridge the start the flooding process.
QUESTION 146
Which of these correctly identifies a difference between the way BPDUs are handled by 802.1w
and 802.1D?
A. 802.1D bridges do not relay BPDUs.
B. 802.1w bridges do not relay BPDUs.
C. 802.1D bridges only relay BPDUs received from the root.
D. 802.1w bridges only relay BPDUs received from the root.
Answer: C
Explanation:
A bridge sends a BPDU frame using the unique MAC address of the port itself as a source address, and a destination address of the STP multicast address 01:80:C2:00:00:00.
There are three types of BPDUs:
Configuration BPDU (CBPDU), used for Spanning Tree computation Topology Change Notification (TCN) BPDU, used to announce changes in the network topology Topology Change Notification Acknowledgment (TCA)
BPDU are Sent Every Hello-Time
BPDU are sent every hello-time, and not simply relayed anymore. With 802.1D, a non-root bridge only generates BPDUs when it receives one on the root port. In fact, a bridge relays BPDUs more
than it actually generates them. This is not the case with 802.1w. A bridge now sends a BPDU with its current information every <hello-time> seconds (2 by default), even if it does not receive any from the root bridge.
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtm l#topic4
QUESTION 147
NBAR supports all of these with the exception of which one?
A. HTTP
B. IP multicast
C. TCP flows with dynamically assigned port numbers
D. non-UDP protocols
Answer: B
Explanation:
Restrictions for Using NBAR
NBAR does not support the following:
More than 24 concurrent URLs, hosts, or Multipurpose Internet Mail Extension (MIME) type matches.
Matching beyond the first 400 bytes in a packet payload in Cisco IOS releases before Cisco IOS Release 12.3 (7)T. In Cisco IOS Release 12.3(7)T, this restriction was removed, and NBAR now supports full payload inspection. The only exception is that NBAR can inspect custom protocol traffic for only 255 bytes into the payload.
Non-IP traffic
Multiprotocol Label Switching (MPLS)-labeled packets – NBAR classifies IP packets only. You can, however, use NBAR to classify IP traffic before the traffic is handed over to MPLS. Use the Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC) to set the IP differentiated services code point (DSCP) field on the NBAR-classified packets and make MPLS map the DSCP setting to the MPLS experimental (EXP) setting inside the MPLS header. Multicast and other non-CEF switching modes Fragmented packets Pipelined persistent HTTP requests
URL/host/MIME classification with secure HTTP
Asymmetric flows with stateful protocols
Packets that originate from or that are destined to the router running NBAR NBAR is not supported on the following logical interfaces:
Fast EtherChannel
Dialer interfaces until Cisco IOS Release 12.2(4) T
Interfaces where tunneling or encryption is used
QUESTION 148
Modified deficit round robin supports which of these functionalities?
A. priority queue
B. weighted fair queues
C. round-robin service of output queues
D. LLQ
Answer: AC
Explanation:
Modified deficit round robin (MDRR)–MDRR, a traffic class prioritization mechanism used only on GSR platforms, incorporates emission priority as a facet of quality of service. MDRR is similar in function to WFQ on non-GSR platforms.
In MDRR, IP traffic is mapped to different classes of service queues. A group of queues is assigned to each traffic destination. On the transmit side of the platform, a group of queues is defined on a per- interface basis; on the receive side of the platform, a group of queues is defined on a per-destination basis. IP packets are then mapped to these queues, based on their IP precedence value. These queues are serviced on a round-robin basis, except for a queue that has been defined to run in either of two ways: a) strict priority mode, or b) alternate priority mode. In strict priority mode, the high priority queue is serviced whenever it is not empty; this ensures the lowest possible delay for high priority traffic. In this mode, however, the possibility exists that other traffic might not be serviced for long periods of time if the high priority queue is consuming most of the available bandwidth.
In alternate priority mode, the traffic queues are serviced in turn, alternating between the high priority queue and the remaining queues.
http://www.cisco.com/en/US/docs/ios/12_0st/12_0st10/feature/guide/10st_cos.pdf
QUESTION 149
A router is connected to an HDLC circuit via a T1 physical interface. The SLA for this link only allows for a sustained rate of 768 kb/s. Bursts are allowed for up to 30 seconds at up to line rate, with a window Tc of 125 ms. What should the Bc and Be setting be when using generic traffic
shaping?
A. Be = 46320000 , Bc = 96000
B. Be = ,768000 Bc = 32000
C. Be = ,128000 Bc = 7680
D. Be = ,0 Bc = 96000
Answer: A
Explanation:
Tc= 125
CIR = 768
What is the Be
T1 = 1.544 Mbps
Bursts are allowed for 30 seconds
Seconds * Bandwidth in bps = Be
30 * 1544000 = Be
30 * 1544000 = 46320000
Be = 46320000
What is Bc?
Bc = Tc * CIR
Bc = 125 * 768
Bc = 96000
Traffic Shaping Parameters
We can use the following traffic shaping parameters:
CIR = committed information rate (= mean time)
EIR = excess information rate
TB = token bucket (= Bc + Be)
Bc = committed burst size (= sustained burst size)
Be = excess burst size
DE = discard eligibility
Tc = measurement interval
AR = access rate corresponding to the rate of the physical interface (so if you use a T1, the AR is approximately 1.5 Mbps).
Committed Burst Size (Bc)
The maximum committed amount of data you can offer to the network is defined as Bc. Bc is a measure for the volume of data for which the network guarantees message delivery under normal conditions. It is measured during the committed rate Tc.
Excess Burst Size (Be)
The number of non-committed bits (outside of CIR) that are still accepted by the Frame Relay switch but are marked as eligible to be discarded (DE). The token bucket is a ‘virtual’ buffer. It contains a number of tokens, enabling you to send a limited amount of data per time interval. The token bucket is filled with Bc bits per Tc.
The maximum size of the bucket is Bc + Be. If the Be is very big and, if at T0 the bucket is filled with Bc + Be tokens, you can send Bc + Be bits at the access rate. This is not limited by Tc but by the time it takes to send the Be. This is a function of the access rate.
Committed Information Rate (CIR)
The CIR is the allowed amount of data which the network is committed to transfer under normal conditions. The rate is averaged over a increment of time Tc. The CIR is also referred to as the minimum acceptable throughput. Bc and Be are expressed in bits, Tc in seconds, and the access rate and CIR in bits per second.
Bc, Be, Tc and CIR are defined per data-link connection identifier (DLCI). Due to this, the token bucket filter controls the rate per DLCI. The access rate is valid per user-network interface. For Bc, Be and CIR incoming and outgoing values can be distinguished. If the connection is symmetrical, the values in both directions are the same. For permanent virtual circuits, we define incoming and outgoing Bc, Be and CIR at subscription time.
Peak = DLCI’s maximum speed. The bandwidth for that particular DLCI.
Tc = Bc / CIR
Peak = CIR + Be/Tc = CIR (1 + Be/Bc)
If the Tc is one second then:
Peak = CIR + Be = Bc + Be
http://www.cisco.com/warp/public/125/21.pdf
QUESTION 150
Which of these tables is used by an LSR to perform a forwarding lookup for a packet destined to
an address within an RFC 4364 VPN?
A. CEF
B. FIB
C. LFIB
D. IGP
Answer: C
Explanation:
Notice: The term Label Switch Router (LSR) refers to any router that has awareness of MPLS labels Label Forwarding Information Base (LFIB) is responsible for forwarding incoming packets based on label as it holds necessary label information, as well as the outgoing interface and next-hop information
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