Subject: Strange multicast addresses

From: Iljitsch van Beijnum <[email-masked]>
Date: Sun, 22 May 2005 19:13:59 +0200

Hi,

Maybe this is a stupid question but I'm stumped... And if this isn't  
the appropriate forum, I apologize but I can't think of another place  
to ask this.

When I execute the netstat -ia command on my FreeBSD or MacOS system,  
I see:

xl0    1500 2001:1af8:2 2001:1af8:2:5::2     33034     -     2866      
-     -
                         ff02:1::1:ff00:2   (refs: 1)
                         ff02:1::2:5b81:5275(refs: 1)
                         ff02:1::1          (refs: 1)
                         ff02:1::1:ff29:2640(refs: 1)

The first and last multicast addresses are the solicited node  
addresses for IPv6 addresses on this interface (never mind the  
encoded scope zone identifier), and the ff02:1::1 address is the all- 
hosts multicast address.

But what about the ff02:1::2:5b81:5275 address? This range doesn't  
show up on http://www.iana.org/assignments/ipv6-multicast-addresses  
and I can't find any application that is listening for this address.  
On the other system it's a different address, but also in ff02:x:: 
2:0:0/96.

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Mon, 23 May 2005 03:35:52 +0900

>>>>> On Sun, 22 May 2005 19:13:59 +0200, 
>>>>> Iljitsch van Beijnum <[email-masked]> said:

>                          ff02:1::1:ff29:2640(refs: 1)

(snip)

> On the other system it's a different address, but also in ff02:x:: 

It's most likely the MD5-hashed multicast group derived from the host
name (See Section 5 of draft-ietf-ipngwg-icmp-name-lookups-11.txt.)
The kernel automatically joins the group (like ff02::1 or
solicited-node multicast addresses), so it's not surprising that you
cannot find any application that explicitly joins the group.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Mon, 23 May 2005 12:38:23 +0200

> cannot find any application that explicitly joins the group.

Right, thanks!

It would be helpful if this address range were registered with the  
IANA, though...

For anyone else who wants to know more: have a look at a KAME ping6  
man page: http://developer.apple.com/documentation/Darwin/Reference/ 
ManPages/man8/ping6.8.html