XMG1930 Series User’s Guide
386
A
PPENDIX
C
IPv6
Overview
IPv6 (Internet Protocol version 6), is designed to enhance IP address size and features. The increase in
IPv6 address size to 128 bits (from the 32-bit IPv4 address) allows up to 3.4 x 10
38
IP addresses.
IPv6 Addressing
The 128-bit IPv6 address is written as eight 16-bit hexadecimal blocks separated by colons (:). This is an
example IPv6 address
2001:0db8:1a2b:0015:0000:0000:1a2f:0000
.
IPv6 addresses can be abbreviated in two ways:
• Leading zeros in a block can be omitted. So
2001:0db8:1a2b:0015:0000:0000:1a2f:0000
can be
written as
2001:db8:1a2b:15:0:0:1a2f:0
.
• Any number of consecutive blocks of zeros can be replaced by a double colon. A double colon can
only appear once in an IPv6 address. So
2001:0db8:0000:0000:1a2f:0000:0000:0015
can be
written as
2001:0db8::1a2f:0000:0000:0015
,
2001:0db8:0000:0000:1a2f::0015
,
2001:db8::1a2f:0:0:15
or
2001:db8:0:0:1a2f::15
.
Prefix and Prefix Length
Similar to an IPv4 subnet mask, IPv6 uses an address prefix to represent the network address. An IPv6
prefix length specifies how many most significant bits (start from the left) in the address compose the
network address. The prefix length is written as “/x” where x is a number. For example,
2001:db8:1a2b:15::1a2f:0/32
means that the first 32 bits (
2001:db8
) is the subnet prefix.
Link-local Address
A link-local address uniquely identifies a device on the local network (the LAN). It is similar to a “private IP
address” in IPv4. You can have the same link-local address on multiple interfaces on a device. A link-
local unicast address has a predefined prefix of fe80::/10. The link-local unicast address format is as
follows.
Table 197 Link-local Unicast Address Format
Global Address
A global address uniquely identifies a device on the Internet. It is similar to a “public IP address” in IPv4. A
global unicast address starts with a 2 or 3.
1111 1110 10
0
Interface ID
10 bits
54 bits
64 bits
