| 1. | By default, what does a router or Layer 3 switch do with multicast packets? |
| Answer: | It drops them because multicast routing is not enabled by default. |
| 2. | By default, what does a Layer 2 switch do with a multicast packet? |
| Answer: | It floods the packet out all ports on the source VLAN, as if it were a broadcast packet. |
| 3. | What high-order bit combination signals that an IP address is used for multicast? |
| Answer: | 1110 |
| 4. | If the IP-to-MAC multicast address mapping is somewhat ambiguous, how can a frame be forwarded to the correct destination group? |
| Answer: | The IP header must be examined in addition to the multicast MAC destination address. |
| 5. | What IP multicast address range is set aside for use only on the local network segment? |
| Answer: | 224.0.0.0 to 224.0.0.255 |
| 6. | For the RPF check, the source IP address is looked up in the unicast routing table. To forward the packet, what should the result of the test be? |
| Answer: | The unicast route to the source must be out the interface where the packet arrived. |
| 7. | What important difference exists between IGMPv1 and IGMPv2? |
| Answer: | Hosts can request to leave a multicast group immediately with IGMPv2. IGMPv1 doesn't have any mechanism for leaving a group other than an aging-out process. |
| 8. | To join a multicast group, what type of message is sent? Where is this message sent? |
| Answer: | An IGMP membership report is sent. The IGMP message is with a destination address of the multicast group itself so that the nearest multicast router will receive it. |
| 9. | What is the purpose of the IGMP querier? |
| Answer: | It is a router that periodically asks all hosts if any of them want to join the multicast group. Interested hosts must respond with a membership report. |
| 10. | For PIM dense mode, how is the multicast tree built? |
| Answer: | The source is the root of the tree, and all dense-mode routers are included by default. After all of these have joined the group, a pruning phase occurs so that routers with no member hosts are pruned off the tree. |
| 11. | Where is the root of the PIM sparse-mode tree located? |
| Answer: | At a rendezvous point (RP) router |
| 12. | With PIM sparse-dense mode, is the PIM mode determined per interface or per group? |
| Answer: | Per group. If the group has an RP, sparse mode is used; otherwise, dense mode is used. |
| 13. | What routing table is used for PIM? |
| Answer: | The unicast routing table is used. PIM does not build or maintain its own multicast routing table. |
| 14. | What command is used to configure an interface for the hybrid PIM mode? |
| Answer: | ip pim sparse-dense-mode |
| 15. | When a switch performs IGMP snooping, what is it snooping for? |
| Answer: | It listens to all IGMP membership reports so that it can learn the location of hosts joining and leaving multicast groups. |
| 16. | What else does a Layer 2 switch need when it is configured for CGMP? |
| Answer: | A multicast router. The router relays group join and leave requests as CGMP packets that the switch can use. |
| 17. | When should IGMP snooping and CGMP be used together on a switch? |
| Answer: | Never; they are mutually exclusive features. |
| 18. | At a trade show, several PCs and servers are connected to a single Layer 2 switch. The switch has CGMP enabled. When a server begins to send video data to a multicast address, what happens to that traffic? |
| Answer: | Even though CGMP is enabled, no multicast router is available to assist the switch with its multicast forwarding decisions. Therefore, the video packets will be flooded out all switch ports on the server's VLAN. |
