Chapter 23: IPv6
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 717
Hop Limit (1 octet): Maximum number of router hops permitted. This number is decremented by one each time the
packet passes through a router. This is identical to the commonly accepted practice in IPv4 for decrementing the TTL
field, although technically the IPv4 TTL is supposed to be decremented once per second. In IPv6, the defined behavior
matches the common IPv4 practice where the counter is simply decremented once per hop.
Source Address (16 octets): 128-bit IPv6 source address.
Destination Address (16 octets): 128-bit IPv6 destination address.
IPv6 Addressing Architecture
Address Notation
IPv6 addresses are 128 bits (16 octets) long displayed as eight 16-bit values in hexadecimal notation separated by colons.
An IPv6 address is composed of a high-order network prefix and a low-order interface identifier with the boundary of the
prefix designated by a slash decimal notation.
For example, the IPv6 unicast address:
2001:01AB:00CD:0001:0000:0000:0000:0001/64
... designates an IPv6 unicast address with:
a 64-bit network prefix of 2001:01AB:00CD:0001
a 64-bit host identifier of 0000:0000:0000:0001
The full form of the address includes all leading zeros, while the preferred form suppresses the leading zeros and the
compressed form replaces a single contiguous sequence of zeros with a double colon (::). In the example of a full form
address shown above, the preferred form is 2001:1AB:CD:1:0:0:0:1/64 and the abbreviated form is 2001:1AB:CD:1::1/64.
The hexadecimal address notation is not case sensitive.
Types and Scope of Addresses
There are three kinds of IPv6 addresses: unicast, multicast, and anycast. Unicast and multicast packets are treated similarly
to unicast and multicast in IPv4. The IPv4 notion of broadcast is absent from IPv6, being replaced by certain forms of
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