Subject: ipv6 multicasting: "interface-local" scope

From: Kristoff Bonne <[email-masked]>
Date: Thu, 14 Apr 2011 19:23:07 +0200

Hi,

(This is a repost of a message I posted yesterday in
linux.network.general but to which I have not seen any replies).

If I understand RFC 4291 correctly, the ipv6 multicast ip-addresses
ffx1:<scope> are "interface local" scope.

In draft-ietf-ipngwg-scoping-arch-02, I read this:
"The interface-local scope spans a single interface only; a multicast
address of interface-local scope is useful only for loopback delivery of
multicasts within a single node, for example, as a form of inter-process
communication within a computer".

This is exactly what I want to do for an application I am working on.

However when I try it and make a small program that sends out UDP
packats to the ipv6 multicast address ff11::1234, I do see them show up
on remote machines on my LAN!
So it looks like these packets do leave my local compute which -I think-
is the opposite of what RFC4291 tells me should happen.

Am I missing something? or is this a bug?

The machine on which I have tested this runs ubuntu 10.04.1 LTE with
kernel 2.6.32-30-generic

Anybody any ideas?

links:
- RFC4291: http://tools.ietf.org/html/rfc4291#section-2.7
- draft-ietf-ipngwg-scoping-arch-02:
http://tools.ietf.org/html/draft-ietf-ipngwg-scoping-arch-02)

Cheerio! Kr. Bonne.