Chapter 23: IPv6
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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configure interface cable-mac 1.0 ipv6 address fc00:cada:c423:c001::1/64
configure interface cable-mac 1 ipv6 nd prefix fc00:cada:c423:c001::/64 off-link
Each configured IPv6 site-local and global address assigned to a cable interface must have its corresponding prefix explicitly
configured as off-link for devices on that same prefix but behind different modems to communicate using that prefix.
Link-local traffic, that is traffic from devices on cable interfaces with an IPv6 link-local destination address is never
forwarded by the C4/c CMTS. All link-local traffic from devices on cable interfaces received by the C4/c CMTS is
terminated at the C4/c CMTS.
IPv6 over Ethernet
IPv6 is transported over ethernet using its own ethertype: 0x86DD. Thus, IPv6 traffic is distinguished at Layer 2 from IPv4
and ARP traffic using ethertypes 0x0800 and 0x0806 respectively. Note that IPv6 does not use ARP to resolve unicast MAC
addresses; rather it relies on the built-in ICMPv6 protocol to provide the equivalent Neighbor Discovery and Duplicate
Address Detection functions found in ARP. This means that only one ethertype is used for all IPv6-related ethernet
transport.
The IPv6 does not use the ethernet MAC broadcast address FFFF.FFFF.FFFF for any purpose — it is replaced by various
forms of ethernet MAC multicast addresses designated for specific purposes. All IPv6 multicast addresses (FF0x::/16) are
directly mapped into ethernet MAC multicast addresses of the form 3333.xxxx.xxxx, where xxxx.xxxx is the low order 32
bits of the IPv6 multicast address. It is expected that host node ethernet interfaces will only listen to specific MAC
multicast addresses, while router node ethernet interfaces will listen to all MAC multicast addresses.
Well-Known Multicast Addresses
RFC-2375, IPv6 Multicast Address Assignments, defines a number of well-known multicast addresses that are reserved for
specific purposes. Nodes are required to respond appropriately if they are of a type that matches the purpose. For
example, the link-local multicast address FF02::2 is the "all-routers" address; therefore, any device that considers itself to
be a router must respond to incoming packets with a destination address of FF02::2 as if the packet's destination was that
router itself.
One of the unique features of IPv6 is the concept of a "solicited node multicast address". This is a link-local scope multicast
address of the form FF02::1:FFxx.xxxx that is intended to replace many of the ARP broadcasts found in IPv4. The solicited
node IPv6 multicast address contains the same low-order 24 bits (xx:xxxx) as the IPv6 unicast address that it represents.
This in turn maps to an ethernet multicast MAC address 3333.FFxx.xxxx that also contains these same low-order 24 bits.
