Hi Karl, The solicited node multicast address is just a pre-filter. Any collision that will be detected with your proposed 32 bit solicited node multicast address will also be detected with a 24 bit solicited node multicast address. How many nodes do you expect to have on your link?
Cheers Suresh > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Karl Auer > Sent: Tuesday, March 01, 2011 3:59 AM > To: IETF IPv6 > Subject: question about solicited node multicast addresses > > How come solicited node multicast addresses use only 24 bits > of the host's IPv6 address? It looks like there is space for > many more; 64 more at a pinch. Using more bits from the host > address would decrease even further the likelihood of two > nodes sharing the same SNM address. > > See RFC 4291, section 2.7.1, page 16. > > I can see why at least one bit is needed to discriminate > between all-nodes and SNM addresses[1], but why use so many bits (8)? > > The only plausible theory I have is that after 8 bits of "ff" > and 16 bits of ethernet multicast prefix (0x3333) are > factored in, there is only room at layer 2 for 24 more bits, > so there is no point having more bits in layer 3. This is not > a satisfying theory because it appears to tie layer 3 > multicast to a specific layer 2 technology (ethernet, with > its 48-bit MAC addresses). > > Regards, K. > > [1] All-nodes L2 multicast 33:33:00:00:00:01 > SNM L2 multicast of 2001:db8:100:200::1 33:33:ff:00:00:01 > SNM L2 with 32 bits instead of 24 bits 33:33:00:00:00:01 > > -- > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > ~~~~~~~~~ > Karl Auer ([email protected]) +61-2-64957160 (h) > http://www.biplane.com.au/kauer/ > +61-428-957160 (mob) > > GPG fingerprint: DA41 51B1 1481 16E1 F7E2 B2E9 3007 14ED 5736 > F687 Old fingerprint: B386 7819 B227 2961 8301 C5A9 2EBC 754B > CD97 0156 > -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
