Defining Address Representation

This topic describes how IPv6 addresses are shown in hexadecimal and the appropriate methods for abbreviation of addresses.

IPv6 Address Representation


• x:x:x:x:x:x:x:x, where x is a 16-bit hexadecimal field

- Case-insensitive for hexadecimal A, B, C, D, E, and F

• Leading zeros in a field are optional:

- 2031:0:130F:0:0:9C0:876A:130B

• Successive fields of 0 can be represented as ::, but only once per address.


- 2031:0000:130F:0000:0000:09C0:876A:130B

- 2031:0:130f::9c0:876a:130b

- 2031::130f::9c0:876a:130b—incorrect

Colons separate entries in a series of 16-bit hexadecimal fields that represent IPv6 addresses. The hexadecimal digits A, B, C, D, E, and F represented in IPv6 are case-insensitive.

IPv6 does not require explicit address string notation. Use the following guidelines for IPv6 address string notations:

■ The leading zeros in a field are optional, so that 09C0 = 9C0 and 0000 = 0.

■ Successive fields of zeros can be represented as "::" only once in an address.

■ An unspecified address is written as "::" because it contains only zeros.

Using the "::" notation greatly reduces the size of most addresses. For example, FF01:0:0:0:0:0:0:1 becomes FF01::1.

Note An address parser identifies the number of missing zeros by separating the two parts and entering 0 until the 128 bits are complete. If two "::" notations are placed in the address, there is no way to identify the size of each block of zeros.

8-16 Building Scalable Cisco Internetworks (BSCI) v3.0 © 2006 Cisco Systems, Inc.

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