IPv6 Address Types

Source-specific multicast

The (IPv4) and FF3x::/32 (IPv6) block is reserved for use by source-specific multicast.

Multicast addresses in IPv6 have the prefix ff00::/8. IPv6 multicast addresses are generally formed from four bit groups, illustrated as follows:

General multicast address format
Bits 8 4 4 112
Field prefix flags scope group ID

The prefix holds the binary value 11111111 for any multicast address. Currently, 3 of the 4 flag bits in the flags field are defined; the most-significant flag bit is reserved for future use. The other three flags are known as R, P and T.

Multicast address flags
Bit Flag 0 1
0 (MSB) (Reserved) (Reserved) (Reserved)
1 R (Rendezvous) Rendezvous point not embedded Rendezvous point embedded
2 P (Prefix) Without prefix information Address based on network prefix
3 (LSB) T (Transient) Well-known multicast address Dynamically assigned multicast address

Similar to unicast addresses, the prefix of IPv6 multicast addresses specifies their scope, however, the set of possible scopes is different. The 4-bit sc (or scope) field (bits 12 to 15) is used to indicate where the address is valid and unique.

Multicast address scope
IPv6 address IPv4 equivalent Scope Purpose
ff00::/16-ff0f::/16   Reserved  
ffx1::/16 Interface-local Packets with this destination address may not be sent over any network link, but must remain within the current node; this is the multicast equivalent of the unicast loopback address.
ffx2::/16 Link-local Packets with this destination address may not be routed anywhere.
ffx3::/16 IPv4 local scope  
ffx4::/16   Admin-local The smallest scope that must be administratively configured.
ffx5::/16   Site-local Restricted to the local physical network.
ffx8::/16 Organization-local Restricted to networks used by the organization administering the local network. (For example, these addresses might be used over VPNs; when packets for this group are routed over the public internet (where these addresses are not valid), they would have to be encapsulated in some other protocol.)
ffxe::/16 Global scope Eligible to be routed over the public internet.

The service is identified in the 112-bit Group ID field. For example, if ff02::101 refers to all Network Time Protocol (NTP) servers on the local network segment, then ff08::101 refers to all NTP servers in an organization's networks. The Group ID field may be further divided for special multicast address types.

The following table is a partial list of well-known IPv6 multicast addresses that are registered with the Internet Assigned Numbers Authority (IANA).

Well-known IPv6 multicast addresses
Address Description
ff02::1 All nodes on the local network segment
ff02::2 All routers on the local network segment
ff02::5 OSPFv3 All SPF routers
ff02::6 OSPFv3 All DR routers
ff02::8 IS-IS for IPv6 routers
ff02::9 RIP routers
ff02::a EIGRP routers
ff02::d PIM routers
ff02::16 MLDv2 reports (defined in RFC 3810)
ff02::1:2 All DHCP servers and relay agents on the local network segment (defined in RFC 3315)
ff02::1:3 All LLMNR (Link-local Multicast Name Resolution) hosts on the local network segment (defined in RFC 4795)
ff05::1:3 All DHCP servers on the local network site (defined in RFC 3315)
ff0x::c Simple Service Discovery Protocol
ff0x::fb Multicast DNS
ff0x::101 Network Time Protocol
ff0x::108 Network Information Service
ff0x::114 Used for experiments