[openib-general] IPv6 multicast address per NIC

[Todd Rimmer]

> From: Or Gerlitz
> Sent: Thursday, February 15, 2007 4:25 AM
> To: Roland Dreier; Hal Rosenstock; openib
> Subject: [openib-general] IPv6 multicast address per NIC
> 
> Hi,
> 
> I see that when IPv6 is enabled in the kernel, the stack joins for a
> --dedicated-- multicast group per each interface. Can anyone here
supply
> me with a pointer to where this is defined, doing a quick look on rfc
> 3307 did not provide an answer.
> 
RFC 2373 defined an IPv6 Solicited Node multicast address which is based
on the IPv6 address of the Node.  Each node supports a unique multicast
(in addition to the assorted multicast addresses for all nodes, all
routers, etc).

>From RFC 2373:
      Solicited-Node Address:  FF02:0:0:0:0:1:FFXX:XXXX

   The above multicast address is computed as a function of a node's
   unicast and anycast addresses.  The solicited-node multicast address
   is formed by taking the low-order 24 bits of the address (unicast or
   anycast) and appending those bits to the prefix
   FF02:0:0:0:0:1:FF00::/104 resulting in a multicast address in the
   range

      FF02:0:0:0:0:1:FF00:0000

   to

      FF02:0:0:0:0:1:FFFF:FFFF

   For example, the solicited node multicast address corresponding to
   the IPv6 address 4037::01:800:200E:8C6C is FF02::1:FF0E:8C6C.  IPv6
   addresses that differ only in the high-order bits, e.g. due to
   multiple high-order prefixes associated with different aggregations,
   will map to the same solicited-node address thereby reducing the
   number of multicast addresses a node must join.

   A node is required to compute and join the associated Solicited-Node
   multicast addresses for every unicast and anycast address it is
   assigned.

Todd Rimmer