Subject: [homenet] Site-local multicast [was: Updating DNS]

From: Gabriel Kerneis <[email-masked]>
Date: Sun, 24 Apr 2016 21:38:34 +0200

On Sun, Apr 24, 2016 at 6:29 PM, Juliusz Chroboczek <
[email-masked]> wrote:
>
> Oh, sure, we Poles are not quite as pessimistic as the Finns.  I'm
> actually of a divided mind here -- I rather like distributed solutions
> (hence prefer mDNS to DDNS) but dislike proxying.

I agree. igmpproxy was such a pain to get right that I now use an ethernet
cable between my DLNA server and receiver.

> Part of me just wishes we'd mandate site-local multicast and do mDNS over
> that.
>

Now you get me curious. How do you do efficient site-local multicast when
you have multiple wifi and ethernet links?

Best,
Gabriel

---

From: Juliusz Chroboczek <[email-masked]>
Date: Sun, 24 Apr 2016 22:14:11 +0200

> Now you get me curious. How do you do efficient site-local multicast
> when you have multiple wifi and ethernet links?

Assuming you've got only transitive links, then any multicast routing
protocol should work fine at the scale we envision for Homenet as long as
it is able to avoid wireless links whenever possible.  Pierre was
suggesting PIM-BIDIR, and actually provided a suitable implementation [1].
Some people have hinted to me in private conversations that they'd prefer
something simpler, perhaps more akin to DVMRP [2] but without the
automatic tunnelling.

If your Homenet depends on non-transitive links (i.e. has meshy bits in
it), then you cannot use RPF [3], so changes to the data plane are
required (see, for example, Section 5 of [4]).  Thankfully, non-transitive
links are outside the scope of Homenet, so I think it would be fine to use
a solution where multicast doesn't cross the meshy bits.

[1] http://mid.gmane.org/[email-masked]
[2] https://en.wikipedia.org/wiki/Distance_Vector_Multicast_Routing_Protocol
[3] https://en.wikipedia.org/wiki/Reverse_path_forwarding
[4] https://tools.ietf.org/html/rfc6621#section-6

-- Juliusz

---

From: Dino Farinacci <[email-masked]>
Date: Sun, 24 Apr 2016 14:00:44 -0700

> something simpler, perhaps more akin to DVMRP [2] but without the

If you don't want any source discovery issues, use Bidir-PIM. 

Dino