Re: [Etherboot-developers] [RFC] Multicast reception....

[<ebi...@ln...>]

Marty Connor <ma...@et...> writes:

> On Fri, 31 May 2002 23:55:36 -0600 Eric W. Biederman
> <ebi...@ln...> wrote:
> >Transmitting multicast packets is trivial and I have completed the
> >implemetation in 10 lines of code.  Receiving multicast packets is
> >more interesting.
> 
> This might somewhat more complicated than it first appears.  Although one
> can make a trivial change at the "kernel" level, every driver may have to
> be changed in order to accomodate this mode of operation.  I seem to
> recall specifically turning off multicast reception in a number of drivers.

Do you recall any specific problems, or performance issues for why you
did that? 

> Some of the older cards we now support may not even reliably be able to
> function in this mode.  Then there's the testing of cards in this new
> mode.  Retransmits and -DCONGESTED may need to be revisted as well.

Cards won't operate reliably if you ask them to receive all packets?

Hmm. Skimming the kernel it has both the concept of interfaces in
promiscuous mode, as well as the concept of interfaces in just
multicast reception mode.  And it seems receiving all multicast
packets is widely implemented, and generally easy to setup.

> Although it sounds like a really cool thing, I advise caution, lots of
> testing, maybe even a revival of the odd-numbered-release branch (maybe
> re-initialized to current production state first or something) to find
> out how well multicast will work.  We also need people who are willing to
> test it in busy networks.

I think I can find a busy network  or two.

> So, my first reaction is "go for it", but carefully ;)

Given the warning I will start with -DALLMULTI so the driver changes
can be enabled/disabled.  For some cards doubtless this will be
promiscuous mode.  But there is no point in asking for more than I
need.  

Eric