Information Technology Reference
In-Depth Information
Because there should be eight blocks of addresses and you have six, you can expand the
double colon to two blocks as follows:
2001:004C:0000:0000:0050:0000:0000:0741
IPv4-Compatible IPv6 Addresses
IPv6 allows for IPv4 compatible IPv6 addresses. In a mixed IPv6/IPv4 environment, the
IPv4 portion of the address requires the last two 16-bit blocks, or 32 bits of the address,
which is represented in IPv4 dotted-decimal notation. The portion of the IPv6 address
preceding the IPv4 information is all 0s. Six hexadecimal 16-bit blocks are concatenated
with the dotted-decimal format. The first 96 bits are 0, and the last 32 bits are used for the
IPv4 address. This form is
x:x:x:x:x:x:d.d.d.d
, where each
x
represents the hexadecimal
digits and
d.d.d.d
is the dotted-decimal representation.
An example of a mixed full address is 0000:0000:0000:0000:0000:0000:100.1.1.1; this ex-
ample can be shortened to 0:0:0:0:0:0:100.1.1.1 or ::100.1.1.1.
RFC 4921 mentions that IPv4-compatible IPv6 addresses have been deprecated since up-
dated IPv6 transition mechanisms no longer use these addresses.
IPv6 Prefix Representation
IPv6 prefixes are represented similar to IPv4, with the following format:
IPv6-address
/
prefix
The
IPv6-address
portion is a valid IPv6 address. The
prefix
portion is the number of
leftmost contiguous bits that represent the prefix. You use the double colon only once in
the representation. An example of an IPv6 prefix is 200C:001b:1100:0:0:0:0:0/40 or
200C:1b:1100::/40.
For another example, look at the representations of the 60-bit prefix 2001000000000ab0:
2001:0000:0000:0ab0:0000:0000:0000:0000/60
2001:0000:0000:0ab0:0:0:0:0/60
2001:0000:0000:ab0::/60
2001:0:0:ab0::/60
The rules for address representation are still valid when using a prefix. The following is not
a valid representation of the preceding prefix:
2001:0:0:ab0/60
The preceding representation is missing the trailing double colon:
2001::ab0/60
2001:0000:0000:0ab0::/60.
