H3C Technologies H3C SecPath F1000-E - Manual (Page 103)

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Internet Control Message Protocol version 4 (ICMPv4) Router Discovery messages, and ICMPv4 Redirect
messages and provides a series of other functions.
Flexible extension headers
IPv6 cancels the Options field in the header and introduces optional extension headers to provide
scalability and improve efficiency. The Options field in the IPv4 packet header contains 40 bytes at most,
whereas the IPv6 extension headers are restricted to the maximum size of IPv6 packets only.
IPv6 Addresses
IPv6 address format
An IPv6 address is represented as a set of 16-bit hexadecimals separated by colons. An IPv6 address is
divided into eight groups, and each 16-bit group is represented by four hexadecimal numbers, for
example, 2001:0000:130F:0000:0000:09C0:876A:130B.
To simplify the representation of IPv6 addresses, zeros in IPv6 addresses can be handled as follows:
• The leading zeros in each group can be removed. For example, the above address can be
represented in a shorter format as 2001:0:130F:0:0:9C0:876A:130B.
• If an IPv6 address contains two or more consecutive groups of zeros, they can be replaced by a
double colon (::). For example, the above address can be represented in the shortest format as
2001:0:130F::9C0:876A:130B.
CAUTION:
A double colon may appear once or not at all in an IPv6 address. Otherwise, the device cannot determine
how many zeros the double colons represent when converting them to zeros to restore a 128-bit IPv6
address.
An IPv6 address consists of two parts: an address prefix and an interface ID, which are equivalent to the
network ID and the host ID of an IPv4 address respectively.
An IPv6 address prefix is written in IPv6-address/prefix-length notation where the IPv6-address is
represented in any of the formats above and the prefix-length is a decimal number indicating how many
leftmost bits of the IPv6 address comprises the address prefix.
IPv6 address types
IPv6 addresses fall into three types: unicast address, multicast address, and anycast address.
• Unicast address: An identifier for a single interface, similar to an IPv4 unicast address. A packet
sent to a unicast address is delivered to the interface identified by that address.
• Multicast address: An identifier for a set of interfaces (typically belonging to different nodes),
similar to an IPv4 multicast address. A packet sent to a multicast address is delivered to all
interfaces identified by that address.
• Anycast address: An identifier for a set of interfaces (typically belonging to different nodes). A
packet sent to an anycast address is delivered to the nearest one of the interfaces identified by that
address. The nearest interface is chosen according to the routing protocols' measure of distance.
NOTE:
There are no broadcast addresses in IPv6. Their function is replaced by multicast addresses.
The type of an IPv6 address is designated by the first several bits called the format prefix. Table 1 lists the
mappings between address types and format prefixes.