Term
| What is the best destination that a host can send a report message to in order to join a specific multicast group? |
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Definition
| A host can send a join message to several possible destination addresses, but to ensure that all group members on a subnet, and any routers listening for members of the group to hear the report, the best destination is to send it to the group address. |
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Term
| What are the benefits of a host sending a report (join) message to the group address? |
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Definition
| Sending reports to the group address eliminates multiple reports on a subnet, since when a query is received, each group member starts a timer based on a random value. The member does not send a report until the timer expires, and because the timers are random, it is much more likely that one member's timer will expire before the other timers. |
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Term
| How do routers on the same subnet keep from sending the same data stream on to the same network? |
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Definition
| Because of routing protocols, the routers are aware of each other, and a way you ensure that only one router forwards the session onto the subnet is to add a designated router, or querier, function to the multicast routing protocol. The querier is responsible for forwarding the multicast stream, and the other router(s) only listen, forwarding the stream only of the querier fails. |
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Term
| Who is responsible for the querier election on a subnet with multiple multicast-capable routers? |
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Definition
| The local group management protocol is responsible for the querier election function, since this protocol must be the same throughout the network. Leaving this function to the routing protocol can be problematic, since there may be multiple routing protocols running on the network, meaning multiple queriers may be elected. |
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Term
| Explain the Any Source Multicast (ASM) delivery mode. |
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Definition
| For the Any Source Multicast delivery mode, an IP multicast receiver host can use any version of IGMP to join a multicast group, which is notated as G in the routing table state notation. By joining this group, the receiver host is indicating that it wants to receive IP multicast traffic sent by any group to group G. |
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Term
| What happens if 2 applications use the same Any Source Multicast group address simultaneously? |
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Definition
| Any Source Multicast requires group address allocation within the network, where at any given time, an ASM group should only be used by a single application. When 2 applications use the same ASM group simultaneously, receiver hosts of both applications will receive traffic from both application sources. |
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Term
| What is Source Specific Multicast (SSM)? |
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Definition
| Source Specific Multicast is a datagram delivery model that best supports one-to-many applications, also known as broadcast applications. SSM is a core network technology for the Cisco implementation of IP multicast targeted for audio and video broadcast application environments. |
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Term
| Explain the Source Specific Multicast (SSM) delivery mode. |
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Definition
| For the SSM delivery mode, an IP multicast receiver host must use IGMPv3 to subscribe to channel (S, G). By subscribing to this channel, the receiver host is indicating that it wants to receive IP multicast traffic sent by source S to group G. |
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Term
| How does Source Specific Multicast handle group address allocation within a network? |
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Definition
| SSM does not require group address allocation within the network, only within each source host, so different applications running on the same source host must use different SSM groups. Different applications running on different hosts can arbitrarily reuse SSM group addresses without causing any excess traffic on the network. |
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