Sign Up
Log In
Exam 400-101 Question id=748 Layer 2 Technologies

Which of the following protocols is used with IPv6 multicast and natively supports SSM?

A. MLDv1
B. MLDv2

Multicast Listener Discovery version 2 (MLDv2) is used with IPv6 multicast and natively supports Source Specific Multicast (SSM). MLD is similar to Internet Group Management Protocol (IGMP) in that both are used to manage multicast group membership information. However, MLD is used on IPv6 multicast networks, whereas IGMP is used on IPv4 multicast networks. IPv6 routers are MLD queriers, and IPv6 hosts are MLD receivers. An MLD host sends a report message to the MLD querier on the subnet to indicate that the host wants to receive multicast traffic. MLD messages are sent with a timetolive (TTL) value of 1, which means that an MLD message is sent only to the next hop.

When SSM is used, a multicast host can specify the source addresses from which it will accept multicast traffic. As a result, SSM uses the (S,G) model instead of the (*,G) model? the S denotes a particular multicast source address, the G denotes the multicast group address, and the * denotes all multicast source addresses.

Protocol Independent Multicast dense mode (PIMDM) routers also use the (S,G) model, but PIMDM is not supported in IPv6 multicast. MLDv1 also supports IPv6 networks? however, it does not natively support SSM. SSM mappings can be used to enable MLDv1 hosts to receive multicast streams using Domain Name System (DNS) or static host nametoIPv6 address mappings. To enable SSM mapping, you should issue the ipv6 mld ssmmap enable command. SSM mapping uses DNS for name resolution by default.

Neither IGMP version 2 (IGMPv2) nor IGMPv3 supports IPv6. IGMPv3 improves upon IGMPv2 by adding support for SSM. Thus an IGMPv3 host can specify the source addresses from which it will accept multicast traffic. If the receivers specifically require SSM, you can enable IGMPv3 multicast with SSM by issuing the ip pim ssm command, the ip pim {sparsemode | sparsedensemode} command, and the ip igmp version 3command. Conversely, an IGMPv2 host cannot use SSM to specify the source address from which it will accept multicast traffic. Therefore, you should issue the ip pim {sparsemode | sparsedensemode | densemode} command to enable IGMPv2 multicast on a router? sparsemode interfaces must also be configured with the ip pim rpaddresscommand. IGMPv2 does not require
the ip igmp version 2 command, because IGMPv2 is used by default. The ip pim rpaddress command statically configures the address of the rendezvous point (RP) on the router. The ip pim sparsemode command enables PIM sparse mode (PIMSM) on an interface. PIMSM adds an interface to the multicast table either when a downstream router sends a join message on that interface or when a member of the multicast group is directly connected to the interface. Otherwise, multicast traffic will not be sent by using the PIMSM interface.