The Internet Assigned Numbers Authority (IANA) has reserved the FF3x::/32 address block for Source-Specific Multicast (SSM) in IPv6, as specified in RFC 4607. These addresses follow the unicast-prefix-based format defined in RFC 3306. In this format, the first 96 bits of the multicast address are constructed to include the multicast scope, flags, and the 64-bit unicast network prefix of the source. The remaining 32 bits are used for the Group ID. Therefore, the FF3X::/96 prefix represents the block of multicast groups that can be created from a specific /64 source network prefix, making it the most structurally significant and correct representation of the SSM range in the given options.

A. FF1X::/16 is a range for transient multicast addresses but is not specifically designated for SSM and does not follow the unicast-prefix-based structure required for SSM.

B. FF3X::/16 is an overly broad range. The IANA allocation for SSM is the more specific FF3x::/32 block, which is a subset of this range.

D. FF7X::/16 is incorrect because the '7' flag (0111) sets the Rendezvous Point (RP) flag, which is a mechanism used for Any-Source Multicast (ASM), not SSM.

1. IETF RFC 4607, "Source-Specific Multicast for IP":

Section 4.1, "IPv6 SSM Addresses": "The IANA has allocated the IPv6 multicast address prefix FF3x::/32 for SSM. This allocation is for addresses that are syntactically "unicast-prefix-based" as defined in [RFC3306]." (This establishes the primary range).

2. IETF RFC 3306, "Unicast-Prefix-based IPv6 Multicast Addresses":

Section 5, "Address Format": This section details the address structure: | 8 | 4 | 4 | 8 | 8 | 64 | 32 |. The sum of the first 6 fields (8+4+4+8+8+64) is 96 bits, which defines the portion containing the network prefix. This makes the /96 boundary structurally significant for defining groups within a source prefix.

3. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Router Configuration Guide, Release 22.10.R1:

Section: IPv6 PIM: "IPv6 SSM is supported for addresses in the FF3x::/32 range. This range is reserved for unicast-prefix-based SSM multicast addresses." (This vendor documentation confirms alignment with the IETF standards).

4. IETF RFC 4291, "IP Version 6 Addressing Architecture":

Section 2.7, "Multicast Addresses": This RFC defines the general format for IPv6 multicast addresses, including the flags field. The 'P' flag (bit 2) being set to 1 indicates an address based on a network prefix, which is a characteristic of the FF3x::/32 range.