IPv6 Multicast Addresses

CD

Reference: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus6000/sw/unicast/6_x/cisco_n6k_layer3_ucast_cfg_rel_602_N2_1/l3_ipv6.pdf

IPv6 multicast addresses are used to communicate with a group of hosts, identified by a single multicast address. Here are the explanations for the two true statements regarding IPv6 multicast addresses:

A. They use the prefix FC80::/8:

This statement is false. The prefix FC00::/7 is used for Unique Local Addresses (ULA), not for multicast addresses. IPv6 multicast addresses use the prefix FF00::/8.

B. If the lifetime parameter is set to 1, the route is permanent:

This statement is false. IPv6 multicast routing protocols use a "time to live" (TTL) or "hop limit" field in the packet header to control the scope of the multicast traffic. However, the TTL field does not control the lifetime of the multicast route. In IPv6 multicast routing, the route is typically created dynamically when the first multicast packet is received, and it is removed when there are no more active multicast groups or when the multicast routing protocol detects that the route is no longer needed.

C. They identify a group of interfaces on different devices:

This statement is true. IPv6 multicast addresses are used to identify a group of interfaces on different devices that are interested in receiving multicast traffic. Each interface can join or leave a multicast group by sending or receiving special control messages. Multicast traffic is delivered to all interfaces that have joined the corresponding multicast group.

D. They use the prefix FF00::/8:

This statement is true. IPv6 multicast addresses use the prefix FF00::/8, which means that the first octet is always "FF". The remaining 7 bits of the first octet are used to define the scope of the multicast address, from 0 (reserved) to 14 (global scope). The last 64 bits of the multicast address represent the multicast group identifier.

E. If the scope parameter is set to 5, the route is local to the node:

This statement is false. The scope parameter in an IPv6 multicast address is used to define the scope of the multicast group, not the scope of the multicast route. The scope parameter can be set to 0 (reserved), 1 (interface-local), 2 (link-local), 3 (subnet-local), 4 (admin-local), 5 (site-local), 8 (organization-local), or 14 (global). The scope of the multicast group determines how far the multicast traffic can be propagated in the network. For example, a site-local multicast group can be heard only within the site, whereas a global multicast group can be heard throughout the entire Internet.