Review Questions

1.	Which of the following commands are necessary in order for multicast to work? (Choose all that apply.) ip mroute cache ip pim [sparse-mode | dense-mode | sparse-dense-mode] ip cgmp ip multicast-routing
2.	Which of the following addresses are within the range of valid IP multi-cast addresses? (Choose all that apply.) 242.127.1.1 224.0.0.1 239.255.255.254 225.128.1.1
3.	What three configuration tasks are necessary to enable multicast Auto-RP? Perform IP multicast routing. Assign the default RP (for existing multicast networks). Assign the RP Mapping Agent. Advertise RP/group associations.
4.	What is the main difference between broadcast and multicast communication? Multicast data is distributed to subscribed hosts on specific groups. Broadcast data is distributed to subscribed hosts on specific groups. Multicast data uses unicast route tables to flood the network instead of using the network's broadcast address. There really is no difference.
5.	What is the destination of the reserved IP multicast address 224.0.0.2? All DVMRP routers All routers All hosts All CGMP-enabled routers
6.	How many layer 3 IP multicast addresses can be represented by the same layer 2 MAC address? 1 23 32 24
7.	Which of the following multicast route notations indicates the operation of sparse mode? (*, G) (G, *) (S, G) (G, S)
8.	What are the primary functions of RP Mapping Agents? (Choose all that apply.) Mapping unicast addresses of all RP routers in a multicast network Sourcing multicast traffic Resolving multicast group/RP conflicts Providing member topologies to the RP routers in the network
9.	Which of the following is a method of limiting the scope of a multicast network? Passive interface applied to border interfaces Distribution lists within an IGP such as EIGRP or OSPF TTL threshold setting on border interfaces RPF settings within the RP routers
10.	What is the layer 2 MAC address for the layer 3 IP address 224.2.127.254? 01-00-5E-02-7E-FF 01-00-5E-02-7F-FE 01-00-5E-00-7E-FF 01-00-5E-00-7F-FE
11.	Which are tools that can be used to troubleshoot multicast connectivity? (Choose all that apply.) Ping show ip mroute traceroute mtrace
12.	Which of the following protocols can hosts use to subscribe to a multicast group? (Choose all that apply.) IBMP IGMPv1 IGMPv2 CGMP DVMRP MOSPF PIM (DM/SM) CBT
13.	From which direction is the mtrace established? From the default RP of the multicast network to the source From the source to the RP From the source to the router interface From the router interface to the source
14.	What two address values does CGMP use compared to IGMP? CGMP uses the USA and GDA. CGMP uses the MAC address and IP address. CGMP uses the GSA and UDA. CGMP uses the MAC address and switch port.
15.	What are the two types of distribution trees? RP trees Multicast trees Shared root trees Source root trees
16.	What command is used to manually configure a router to be an RP? ip multicast RP ip_address ip pim RP ip_address ip pim rp-address ip_address ip igmp rp-address ip_address
17.	Which of the following criteria activates an interface that is configured to use dense mode? (Choose all that apply.) Directly connected hosts Directly connected PIM routers Router configured as a border router When the interface receives a prune statement from a directly connected PIM router
18.	What are two types of shared root tree distributions? Unidirectional Unicast Multidirectional Bidirectional
19.	Which criteria activates an interface in sparse mode when the interface is configured to use sparse-dense mode? (Choose all that apply.) Directly connected DVMRP neighbor. Explicit join request. Any PIM-configured interface is made active. The interface has directly connected hosts.
20.	How does PIM DM differ from PIM SM? (Choose all that apply.) PIM DM assumes that all PIM neighbors have active members directly connected and initially forwards multicast data out every interface. PIM SM requires an explicit join from a router before the router is added to the shared tree. PIM DM is based on a source root tree distribution mechanism. PIM SM is based on bidirectional shared root tree distribution.

Answers

1.	B, D These two commands must be entered for multicast forwarding to work. The ip mroute cache command enhances performance but is not necessary. CGMP is necessary only when hosts are connected to a router via a Catalyst switch using CGMP.
2.	B, C, D The first response is outside of the valid range for IP multicast addresses. The other choices are valid host addresses within the range.
3.	B, C, D IP multicast routing is not part of the Auto-RP configuration.
4.	A Broadcast communications use the broadcast IP or MAC address to communicate information to all hosts. Multicast data is sent only to hosts subscribing to groups that are active on the network.
5.	B IANA reserved the address 224.0.0.2 to indicate all local multicast routers. This address is not forwarded by any routers in the network.
6.	C Due to the lost 5 bits in the mapping, 32 IP addresses may be represented by the same multicast MAC address (25 = 32).
7.	A (S, G) and (*, G) are the only valid notations. (*, G) indicates a shared root tree distribution. Sparse mode uses shared root trees.
8.	A, C RP Mapping Agents keep track of all RP routers in the network via their unicast addresses. They then provide the nearest RP for the multicast groups it sources to all leaf routers in the multicast network.
9.	C The correct way to limit the scope of the multicast network is to configure TTL thresholds for external or border interfaces. RPF is used strictly for reverse path lookup.
10.	B The MAC prefix is 01-00-5E. You know you don't have to worry about the lost bits because the second octet of the IP address is less than 127. Therefore, the value is 02. The last two octets are mapped with no problem.
11.	A, B, D Traceroute is used for unicast connectivity; mtrace, however, is used for multicast connectivity.
12.	B, C CGMP is Cisco's proprietary version of IGMP. IBMP is not a valid protocol. The other protocols are for routing purposes and group management within a network.
13.	C From the examples given in this chapter, you can see that the path is established from the source toward the multicast router interface.
14.	A The USA is the Unicast Source Address (the unique MAC address of the machine) and the GDA is the Group Destination Address (the newly mapped layer 2 multicast MAC address). By using these two values, the switch knows which port to make a CAM entry for.
15.	C, D Multicast trees don't exist. Some protocols that are based in shared root trees can create RPTs (or RP trees) that are parallel to the shortest path tree, but this is a flavor of shared root tree distribution.
16.	C The correct syntax is provided by the third answer. The other answers are not valid.
17.	A, B Hosts activate the interface through membership reports. PIM interfaces automatically receive multicast forwarding until a prune request is received.
18.	A, D We are discussing multicast in this chapter, so unicast is not a valid answer. Because there are only two directions on a tree, the correct answers are bidirectional and unidirectional.
19.	A, B, D A PIM-configured interface is considered active only when in dense mode.
20.	A, B, C The problem with the last answer is that PIM SM is based on unidirectional shared root tree distribution. The other answers are correct.