Administrator Guide

• Next Header (1 byte)
This eld identies the type of header following the Hop-by-Hop Options header and uses the same values.
• Header Extension Length (1 byte)
This eld identies the length of the Hop-by-Hop Options header in 8-byte units, but does not include the rst 8 bytes. Consequently, if the
header is less than 8 bytes, the value is 0 (zero).
• Options (size varies)
This eld can contain one or more options. The rst byte if the eld identies the Option type, and directs the router how to handle the
option.
00 Skip and continue processing.
01 Discard the packet.
10 Discard the packet and send an ICMP Parameter Problem Code 2 message to the packet’s Source IP Address
identifying the unknown option type.
11 Discard the packet and send an ICMP Parameter Problem, Code 2 message to the packet’s Source IP Address only
if the Destination IP Address is not a multicast address.
The second byte contains the Option Data Length.
The third byte species whether the information can change en route to the destination. The value is 1 if it can change; the value is 0 if it
cannot change.
Addressing
IPv6 addresses are normally written as eight groups of four hexadecimal digits, where each group is separated by a colon (:).
For example, 2001:0db8:0000:0000:0000:0000:1428:57ab is a valid IPv6 address. If one or more four-digit group(s) is 0000, the zeros may
be omitted and replaced with two colons(::). For example, 2001:0db8:0000:0000:0000:0000:1428:57ab can be shortened to
2001:0db8::1428:57ab. Only one set of double colons is supported in a single address. Any number of consecutive 0000 groups may be
reduced to two colons, as long as there is only one double colon used in an address. Leading and/or trailing zeros in a group can also be
omitted (as in ::1 for localhost, 1:: for network addresses and :: for unspecied addresses).
All the addresses in the following list are all valid and equivalent.
• 2001:0db8:0000:0000:0000:0000:1428:57ab
• 2001:0db8:0000:0000:0000::1428:57ab
• 2001:0db8:0:0:0:0:1428:57ab
• 2001:0db8:0:0::1428:57ab
• 2001:0db8::1428:57ab
• 2001:db8::1428:57ab
IPv6 networks are written using classless inter-domain routing (CIDR) notation. An IPv6 network (or subnet) is a contiguous group of IPv6
addresses the size of which must be a power of two; the initial bits of addresses, which are identical for all hosts in the network, are called
the network's prex.
A network is denoted by the rst address in the network and the size in bits of the prex (in decimal), separated with a slash. Because a
single host is seen as a network with a 128-bit prex, host addresses may be written with a following /128.
For example, 2001:0db8:1234::/48 stands for the network with addresses 2001:0db8:1234:0000:0000:0000:0000:0000 through
2001:0db8:1234:::::.
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IPv6 Routing