Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 670)

IPv6 Introduction
Software Reference for x310 Series Switches
26.4 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
■ The Loopback address, consisting of ::1, which is the equivalent of the IPv4 loopback
address, and allows a host to send packets to itself.
■ The Unspecified address, consisting of ::, which is the equivalent of the IPv4
unspecified address, and is used as a source address by hosts during the
autoconfiguration process.
Anycast addresses
An anycast address is a unicast address that is attached to more than one interface. If a
packet is sent to an anycast address it is delivered to the nearest interface with that
address, with the definition of “nearest” depending on the protocol used for routing.
Anycast addresses can be assigned to routers only, and packets cannot originate from an
anycast address. A router must be configured to know that it is using an anycast address
because the address format cannot be distinguished from that of a unicast address.
Only one anycast address has been predefined: the subnet-router address. The subnet-
router address sends messages to the nearest router on a subnet and consists of the
subnet’s prefix followed by zeros.
IPv6 Headers
The basic unit of data sent through an internet is called a packet in IPv6. A packet consists
of a header followed by the data. The following figure shows the IPv6 packet.
Figure 26-1: IPv6 packet
1 2 3 4 5 6 7 8 9 0
1
Diff Serv
Payload Length Next Header
128-bit source IP address
128-bit destination IP address
User data
1 2 3 4 5 6 7 8 9 0
2
1 2 3 4 5 6 7 8 9 0
3
1 0
IPv61
Ver
Optional extension headers
Flow Label
Hop Limit