Configuration Guide Configuring IPv6
Among global unicast addresses, there is a type of IPv4-embedded IPv6 addresses, including IPv4-compatible IPv6
addresses and IPv4-mapped IPv6 addresses. They are used for interconnection between IPv4 nodes and IPv6 nodes.
The format of an IPv4-compatible IPv6 address is as follows:
Figure 3-5
The format of an IPv4-mapped IPv6 address is as follows:
Figure 3-6
IPv4-compatible IPv6 addresses are mainly used on automatic tunnels. Nodes on automatic tunnels support both IPv4
and IPv6. Using these addresses, IPv4 devices transmit IPv6 packets over tunnels. At present, IPv4-compatible IPv6
addresses have been abolished. IPv4-mapped IPv6 addresses are used by IPv6 nodes to access IPv4-only nodes. For
example, if the IPv6 application on an IPv4/IPv6 host requests to resolve the name of an IPv4-only host, the name server
dynamically generates an IPv4-mapped IPv6 address and returns it to the IPv6 application.
Multicast Addresses
The format of an IPv6 multicast address is as follows:
| 8 | 4 | 4 | 112 bits |
+--------+----+----+---------------------------------------------+
|11111111|flgs|scop| group ID |
+--------+----+----+---------------------------------------------+
The first byte in the address is all 1s, representing a multicast address.
Flag field
The flag field consists of four bits. Currently only the fourth bit is specified to indicate whether this address is a known
multicast address assigned by the Internet Assigned Numbers Authority (IANA) or a temporary multicast address in a
certain scenario. If the flag bit is 0, this address is a known multicast address. If the flag bit is 1, this address is a
temporary multicast address. The remaining three flag bits are reserved for future use.
Scope field
The scope field consists of four bits to indicate the multicast range. That is, a multicast group includes the local node, local
link, local site, and any node in the IPv6 global address space.
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