Ensurepass
2013 Latest Cisco 350-001 Exam Section 3: Distribution Trees (9 Questions)

QUESTION NO: 1 In an IP multicast network, the more sources an application has, the less frequently traffic is sent from each end. Each time a source starts to send packets, protocol operations take place and a forwarding state is established. For applications with a large number of sources, this state can time-out before the source would to only create a large number of sources, this state can time-out before sources would not only create a large amount of forwarding state (requiring memory), but they could also require high CPU usage o the routing processor due to the accounting of frequently changing state. In addition, the signaling within the router between the routing processor and forwarding hardware can become another potential bottleneck of continuously large amount of traffic signaling must go to the routing processor and equally large amounts of forwarding state changes must go to the forwarding engine(s).
The Testking network is implementing IP multicast, and they wish to avoid the problems described above. Based on this information, what IP multicast technology would you recommend?
Caution: This protocol should avoid maintaining source-specific forwarding state, thereby reducing the amount of memory needed by the number of sources per multicast group, requiring much less traffic signaling in the protocol, preventing the “bursty source” problem, saving on CPU requirements for protocol operations and avoiding potential internal performance limits.
A. PIM Dense Mode (PIM DM)
B. PIM Sparse Mode (PIM SM)
C. Distance Vector Multicast Routing Protocol (DVMRP)
D. Multicast Open Shortest Path First (MOSPF)
E. Bi-Directional PIM
Answer: E
Explanation:
Bidirectional-PIM is a variant of the Protocol Independent Multicast (PIM) suite of routing protocols for IP multicast. In PIM, packet traffic for a multicast group is routed according to the rules of the mode configured for that multicast group. The Cisco IOS implementation of PIM supports three modes for a multicast group:
1.
Bidirectional mode
2.
Dense mode
3.
Sparse mode A router can simultaneously support all three modes or any combination of them for different multicast groups. In bidirectional mode, traffic is routed only along a bidirectional shared tree that is rooted at the rendezvous point (RP) for the group. In bidir-PIM, the IP address of the RP acts as the key to having all routers establish a loop-free spanning tree topology rooted in that IP address. This IP address need not be a router, but can be any unassigned IP address on a network that is reachable throughout the PIM domain. Using this technique is the preferred configuration for establishing a redundant RP configuration for bidir-PIM.
In PIM dense mode (PIM-DM), PIM-SM, and most other multicast routing protocols such as Distance Vector Multicast Routing Protocol (DVMRP) and Multicast Open Shortest Path First (MOSPF), protocol operations and maintenance of packet forwarding state depend on signaling the presence or expiration of traffic (where “signaling” refers to both the packet forwarding engine to routing protocol process within the routers and the packet exchange part of the routing protocol). Triggering PIM assert messages, PIM register messages, and source tree forwarding state are all examples of traffic signaling. There are several advantages to traffic signaling, but they can lead to problems for applications with a large number of sources. For example, the more sources an application has, the less frequently traffic is sent from each sender. Each time a source starts to send packets, protocol operations take place and forwarding state is established. For applications with a large number of sources, this state can time out before the source sends again, resulting in “bursty sources.” Therefore, applications with a large number of sources would not only create a large amount of forwarding state (requiring memory), but they also could require high CPU usage on the Route Processor due to the accounting of frequently changing state. In addition, the signaling within the router between the Route Processor and forwarding hardware can become a bottleneck if continuously large amounts of traffic signaling must go to the Route Processor and equally large amounts of forwarding state changes must go to the forwarding engines. Bidir-PIM solves all these problems. Not only does bidir-PIM avoid maintaining source-specific forwarding state, therefore reducing the amount of memory needed by the number of sources per multicast group, but it also does not require any traffic signaling in the protocol. Thus, bidir-PIM prevents the “bursty source” problem, saving on CPU requirements for protocol operations and avoiding potential router internal performance limits.
Reference:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1612/products_feature_guide09186a0080080a41.htm

QUESTION NO: 2
You are a technician at TestKing. Your newly appointed TestKing trainee wants to know
which IP protocol is used to send PIMv2 control messages.
What would your reply be?

A. UDP
B. TCP
C. BGP
D. Protocol number 107
E. Protocol number 103
Answer: E
Explanation:
All PIM control messages have protocol number 103.
Reference:
http://www.ietf.org/proceedings/99mar/I-D/draft-ietf-pim-v2-dm-01.txt

QUESTION NO: 3
IP multicast addresses in the range of 224.0.0.0 through 224.0.0.255 are reserved for what purpose?
A. It is reserved for Administratively Scoped multicast traffic intended to remain inside a private network.
B. It is reserved for Administratively Scoped multicast traffic that is not supposed to be transmitted onto the Internet.
C. It is reserved for link-local multicast traffic consisting of network control messages that is not supposed to leave the local subnet.
D. Any valid multicast data stream used by multicast applications.
E. Global Internet multicast traffic intended to travel throughout the Internet.
Answer: C
Explanation:
As found in RFC1112. These addresses are used by many routing protocols such as OSPF and RIPv2, in order to sent updates to all neighbors on the same segment.
Incorrect Answers:
Administratively Scoped IP multicast addresses are contained in the
239.0.0.0-239.255.255.255 range. (Not A, Not B)
The 224.0.0.0/8 network range is not intended to be used outside of the local subnet link.
(Not D, Not E)

QUESTION NO: 4
Which of the following PIMv2 Sparse mode control messages are also used in PIM Dense mode? (Choose all that apply.)
A. Graft
B. Join
C. Prune
D. Register
E. Assert
F. Hello
G. Register
Answer: B, C, E, F
PIM-DM uses the following PIMV2 messages.
-Hello -Join/Prune -Graft -Graft-Ack -Assert
PIM-SM uses the following PIMV2 messages
-Hello -Bootstrap -Candidate-RP-Advertisement -Join/Prune -Assert -Register -Register-Stop
Reference:
‘CCIE Professional Development Routing TCP/IP Volume 2’ in the section
‘Understanding IP Multicast Routing’ pages 475 and 488.

QUESTION NO: 5
What best describes the Source Specific Multicast (SSM) functionality?

A. SSM is an extension of the DVMRP protocol that allows for an efficient data delivery mechanism in one-to-many communications.
B. SSM requires MSDP to discover the active sources in other PIM domains.
C. In SSM routing of multicast traffic is entirely accomplished with source trees. The RP is used to direct receivers to the appropriate source tree.
D. Using SSM, the receiver application can signal its intention to join a particular source by using the INCLUDE mode in IGMPv3.
E. None of the above
Answer: D
Explanation:
The Internet Standard Multicast (ISM) service is described in RFC 1112, Host Extensions for IP Multicasting. This service consists of the delivery of IP datagrams from any source to a group of receivers called the multicast host group. The datagram traffic for the multicast host group consists of datagrams with an arbitrary IP unicast source address S and the multicast group address G as the IP destination address. Systems will receive this traffic by becoming members of the host group. Membership to a host group simply requires signalling the host group through IGMP Version 1, 2, or 3. In SSM, delivery of datagrams is based on (S, G) channels. Traffic for one (S, G) channel consists of datagrams with an IP unicast source address S and the multicast group address G as the IP destination address. Systems will receive this traffic by becoming members of the (S, G) channel. In both SSM and ISM, no signalling is required to become a source. However, in SSM, receivers must subscribe or unsubscribe to (S, G) channels to receive or not receive traffic from specific sources. In other words, receivers can receive traffic only from (S, G) channels to which they are subscribed, whereas in ISM, receivers need not know the IP addresses of sources from which they receive their traffic. The proposed standard approach for channel subscription signalling utilizes IGMP INCLUDE mode membership reports, which are supported only in IGMPv3.
Incorrect Answers:
A. SSM is associated with PIM in IPv6 multicast networks. It is not associated with DVMP.
B. SSM builds off of PIM-SM, but also requires an update to IGMP. IGMP version 3 includes a larger header, where the source address can be specified, in addition to the group address. This means that a router no longer needs to communicate with an RP in order to locate the source, and also means that MSDP is no longer needed since its only purpose is to pass information among RPs.
C. PIM-SSM is made possible by IGMPv3. Because hosts can now indicate interest in specific sources using IGMPv3, PIM can create state directly along the path to those sources using SSM. SSM does not require a rendezvous point (RP) to operate.

QUESTION NO: 6 The TestKing network is setting up a VPN for the IP multicast traffic. What best describes the MDT role in MVPN operations?
A. PE routers that have CE routers who are intended recipients of the data only join data MDT. PE routers signal use of data-MDT via a UDP packet on port 3232, which is sent via the default MDT: This packet contains an all-PIM routers message, indicating the group is joined if required.
B. CE routers do not have a PIM adjacency across the provider network with remote CE routers, but rather have an adjacency with their local routes an the PE router. When the PE router receives an MDT packet. It performs an RPF check. During the transmission of the packet through the Provider network, the normal RPF rules apply. However, at the remote’s PE, the router needs to ensure that the originating PE router was the correct one for that CE. It does this by checking the BGP next hop address of the customer’s packet’s source address. This next hop address should be the source address of the MDT packet. The PE also checks that there is a PIM neighbor relationship with the remote PE.
C. A unique Group address is required to be used as MDT for each particular customer. A unique source address for the Multicast packet in the provider network is also required. This source address is recommended to be the address of the loopback interface, which is used as the source for the IBGP, as this address is used for the RPF check at remote PE.
D. PE routers are the only routers that need to be MVPN aware and able to signal to remote PE’s information regarding the MVPN. It is therefore fundamental that all PE routers have a BGP relationship with each other. Either directly or via a Route Reflector. The source address of the Default-MDT will be the same address used to source the IBGP sessions with the remote PE routers that belong to the same VPN and MVRF.
E. All of the above.
Answer: E
Explanation:
Cisco MVPN Details:
While there are significant deployment obstacles to each of the preceding MVPN

this includes both the P and PE routers.
2. IP Multicast is a mature technology that has been deployed since Cisco IOS Software
10.0. This minimizes risk for the provider network, because a new feature will not have to
be introduced into its core to support MVPNs. Multicast Domain Solution This method originally had less than optimal performance, because it requires that all PE routers connected to a customer receive all of that customer’s Multicast data regardless of the presence of an interested receiver in that location. When enhancements resolved this characteristic with a new methodology, it became a truly attractive solution.
Figure 3 Default MDT Concept
The aforementioned enhancement is the addition of ephemeral trees that are created `on the fly’. These trees distribute multicast group data that exceeds a certain configured threshold of Bandwidth (BW) to only those PE who have joined this new tree. These are tress are called MDT-data trees. The word data is appended as these groups are designed to be used for groups that will require a higher amount of bandwidth to deliver their data.
Figure 4 Data MDT Concept This diagram indicates that the Data MDT is only joined by those PE routers that have CE routers who are intended recipients of the data. PE routers signal use of Data-MDT via a UDP packet on port number 3232, which is sent via the default MDT. This packet contains an all-PIM routers message, indicating the group to be joined if required. Interaction of Customer and Providers Multicast Network It is important to remember that the customer’s IP Multicast network has no relationship to the provider’s multicast network. From the perspective of the provider, the customer’s IP Multicast packets are merely data to the provider’s distinctive IP Multicast network. It is important to understand that PIM, and in particular PIM-SM, are the only supported multicast protocols for MVPN. Bi-Dir PIM may be supported in the future, when it is deemed stable enough for the core of a provider network.
Figure 5 Customer PIM Adjacencies CE routers do not have a PIM adjacency across the provider network with remote CE routers, but rather have an adjacency with their local routers and the PE router. When the PE router receives an MDT packet, it performs an RPF check. During the transmission of the packet through the Provider network, the normal RPF rules apply. However, at the remote’s PE, the router needs to ensure that the originating PE router was the correct one for that CE. It does this by checking the BGP next hop address of the customer’s packet’s source address. This next hop address should be the source address of the MDT packet. The PE also checks that there is a PIM neighbourship with the remote PE. Currently, only a single MVRF is supported per customer. This limitation precludes the customer also receiving Internet or any other outside domain’s Multicast traffic A unique Group address is required to be used as MDT for each particular customer. A unique source address for the Multicast packet in the provider network is also required. This source address is recommended to be the address of the loopback interface, which is used as the source for the IBGP, as this address is used for the RPF check at remotePE. If the provider uses MDT-data groups, then these will also need to be configured. These MDT-data groups must be unique for each customer. The PE routers must have a PIM adjacency to each other. No other routing protocols may use these MTIs.
Figure 6
Provider’s PIM Adjacencies

BGP Requirements PE routers are the only routers that need to be MVPN aware and able to signal to remote PE’s information regarding the MVPN. It is therefore fundamental that all PE routers have a BGP relationship with each other. Either directly or via a Route Reflector. The source address of the Default-MDT will be the same address used to source the iBGP sessions with the remote PE routers that belong to the same VPN and MVRF. When PIM-SSM is used for transport inside the provider core, it is via this BGP relationship that the PEs indicate that they are MVPN capable and provide for source discovery. This capability is indicated via the updated BGP message.
Reference:
http://www.cisco.com/en/US/tech/tk828/technologies_white_paper09186a00800a3db6.shtml

QUESTION NO: 7 An enterprise customer runs their core network as an ISP network where they have different Autonomous Systems (AS). The BGP core runs OSPF for Intra-connection only. Data center A is in AS 1, data center B is in AS 2, and data center C is in AS 3. The remote locations will be running an IGP and redistribute their routes into BGP core. They would like to enable multicast throughout their network to support multicast applications.
Based upon the scenario, what would be the LEAST EFFECTIVE way to implement IP multicast?
A. This network runs essentially as an ISP’s network with a BGP core and different AS. To implement multicast in this network they can enable MBGP over the BGP backbone.
B. This is customer’s internal network and not a transit provider in the inter-domain SP routing. As log as there is no incongruence (between multicast and unicast topologies), there is no need to run MBGP. They simply run PIM-SM and MSDP for redundancy.
Leading the way in IT testing and certification tools, www.testking.com
– 357 –
C. Running MBGP, besides BGP, should present negligible overhead and if done together with the introduction of IP multicast will help to avoid problems later on when the network has grown and some incongruence needs to be supported. At that point, the customer may need to upgrade to MBGP throughout the network to have the transitive nature of incongruence supported correctly, and this may then become an obstacle in deployment. Therefore, MBGP should be implemented.
D. It should be determined what IP multicast applications the customer is intending to run. Source Specific Multicast (SSM) should be recommended to the customer, since it would allow them to overcome MSDP and thus reduce the complexity of IP multicast in their deployment.
E. PIM uses the unicast routing information to perform the multicast forwarding function. They can simply implement Inter AS PIM to exchange the multicast routing information. This would be the easiest way to implement multicast in the current network where they leverage all the current unicast routing protocol information to populate the multicast routing table, including Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest path First (OSPF), Border Gateway Protocol (BGP), and static routes. This approach would also cause less processing on the routers as PIM does not send and receive routing updates between routers.
Answer: B
Explanation:
The 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) in different domains. Each PIM-SM domain uses its own rendezvous points and does not need to depend on them in other domains. A rendezvous point runs MSDP over TCP to discover multicast sources in other domains. MSDP is also used to announce sources sending to a group. These announcements must originate at the domain’s Rendezvous Point. MSDP depends heavily on MP-BGP for interdomain operation. Because of this, choice B is the least effective choice since it recommends running MSDP without MGBP. Reference: http://www.cisco.com/univercd/cc/td/doc/product/software/ios111/cc111/mbgp.htm

QUESTION NO: 8 TestKing.com runs a large IP multicast network with thousands of sources and thousands of groups and uses (S, G) entries for forwarding. The applications that are using IP multicast do not require a minimum latency and there is a sever impact on resources on routers and high memory consumption from the size of the multicast routing table.
What would be the right solution in this particular scenario which will decrease the resource issues on the routers, reduce the amount of memory needed by the large multicast routing tables and minimize the amount of state in each router?
A. Continue using (S, G) entries but add a rendezvous point (RP) in the topology
B. Use (*,G) entries with sources trees and a rendezvous point (RP) in the topology
C. Use shared trees with a rendezvous point (RP) in the topology
D. Use combination of source trees and shared trees without rendezvous point (RP) in the topology
E. Use PIM Sparse mode with (S,G) and (*,G) entries
Answer: C
Explanation:
Shortest path trees have the advantage of creating the optimal path between the source and the receivers. This guarantees the minimum amount of network latency for forwarding multicast traffic. This optimization does come with a price, though: The routers must maintain path information for each source. In a network that has thousands of sources and thousands of groups, this can quickly become a resource issue on the routers. Memory consumption from the size of the multicast routing table is a factor that network designers must take into consideration. Unlike source trees that have their root at the source, shared trees use a single common root placed at some chosen point in the network. This shared root is called the rendezvous point (RP).Shared trees have the advantage of requiring the minimum amount of state in each router. This lowers the overall memory requirements for a network that allows only shared trees. The disadvantage of shared trees is that, under certain circumstances, the paths between the source and receivers might not be the optimal paths-which might introduce some latency in packet delivery. Network designers must carefully consider the placement of the RP when implementing an environment with only shared trees.
Incorrect Answers:
A, E: Because of the potentially large number of difference multicast sources in this particular network, the use of individual (S, G) entries should be avoided.
B, D: The simplest form of a multicast distribution tree is a source tree whose root is the source of the multicast tree and whose branches form a spanning tree through the network to the receivers. Because this tree uses the shortest path through the network, it is also referred to as a shortest path tree (SPT). The shortest-path tree requires more memory than the shared tree, but reduces delay. Because we want to reduce the amount of memory needed, these choices are incorrect.
Reference:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ipmulti.htm#xtocid18

QUESTION NO: 9
In the TestKing IP multicast network with many sources which are also receivers,
what protocol is used to allow the use of the same shared tree for traffic from
sources towards RP and from RP towards receivers?

A. PIM Dense Mode (PIM DM)
B. PIM Sparse Mode (PIM SM)
C. Bidirectional PIM
C. Distance Vector Multicast Routing Protocol (DVMRP)
D. Multicast Open Shortest Path First (MOSPF)
Answer: C
Explanation:
Bidirectional-PIM is a variant of the Protocol Independent Multicast (PIM) suite of routing protocols for IP multicast. In PIM, packet traffic for a multicast group is routed according to the rules of the mode configured for that multicast group. The Cisco IOS implementation of PIM supports three modes for a multicast group:
1.
Bidirectional mode
2.
Dense mode
3.
Sparse mode A router can simultaneously support all three modes or any combination of them for different multicast groups. In bidirectional mode, traffic is routed only along a bidirectional shared tree that is rooted at the rendezvous point (RP) for the group. In bidir-PIM, the IP address of the RP acts as the key to having all routers establish a loop-free spanning tree topology rooted in that IP address. This IP address need not be a router, but can be any unassigned IP address on a network that is reachable throughout the PIM domain.
Figure1: Unidirectional Shared Tree and Source Tree

Ensurepass offers Latest 2013 CCIE 350-001 Real Exam Questions , help you to pass exam 100%.

Comments are closed.