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From Colm MacCarthaigh <c...@stdlib.net>
Subject Re: [PATCH] Multicast Support
Date Fri, 31 Dec 2004 04:07:17 GMT
On Thu, Dec 30, 2004 at 07:46:55PM -0800, Paul Querna wrote:
> I haven't done anything with SSM, but I agree it would be nice to have a 
> single API if this is a feature that will be widely used.

It's already in wide use in some spheres, it's the only form of
multicast that has realistic DoS prevention (with ASM, arbitrary
multicast users can trivially join and flood a group id). I'll have at
least on APR-based SSM implementation ready in a few months anyway, for
widescale virus signature updating.

> >Passing "iface" as a sockaddr is not going to be portable, the API's on
> >some systems (Win32 and Linux, using IPv6) for example prefer interface
> >names as the references. Using a string might be better, as it's
> >possible to convert strings to interface numbers ( if_nametoindex() ) and
> >sockaddr's ( inet_addr() ).
> 
> I made is a sockaddr, because I believed that to be the most portable.

Same here, and then I ran into problems ...

> Interface names are per-OS. (eg win32, linux, freebsd, and solaris are 
> all different). This means if I want cross platform or even cross 
> machine configuration, it must not use the interface name, but a network 
> address. (Cross Machine: eg, some machines have Intel Cards, others have 
> Broadcom, in FreeBSD these have different interface names.)
> 
> I welcome a better solution... :)

I resorted to user specifying either something like "eth0" or "1.1.1.1"
depending on their platform. One very ugly solution, but about all that
is portable. Even this isn't foolproof, there is no self-consistent way
between IPv4 and IPv6 to do this on win32.

For the *nix's, some consistency can be got by abandoning the ip_mreq
API and using the group_req one instead - but this is flaky, on *BSD you
need to running a bleeding-edge KAME stack and on Linux you need to
manually define the structures and defines, because the system headers
are broken (oh and you need to be running a pretty recent 2.6 kernel).
But ultimately, the group_req API is far superiour technically.

> I thought that for any OS that prefers the interface name/number, we can 
> always map the sockaddr to that interface pretty easily.

Win32 with IPv6 was my stumbling block with that approach :/ But it's
probably best ignored for these purposes. 

I've tested on Linux anyway, the send/recv apps work fine in IPv6, recv
works fine in IPv4, there's a kink in my system for sending IPv4
- but I havn't had a chance to look at it yet, I doubt it's anything in
  the multicast code though, since sending packets should be identical
for unicast and multicast.

I'll be back in my dev environment on Tuesday, where I can subject it to
the full rigours of our multicast test-lab and feed-back more, I'll
submit some group_req-based SSM code at some point too (unless someone
beats me to it).

-- 
Colm MacCárthaigh                        Public Key: colm+pgp@stdlib.net

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