linux-kernel - Re: When does Linux drop UDP packets?

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Date:	Fri, 5 Jun 2009 20:29:34 +0100
From:	Alexander Clouter <alex@...riz.org.uk>
To:	david@...g.hm
Cc:	linux-kernel@...r.kernel.org, sefi@...-f-i.de
Subject: Re: When does Linux drop UDP packets?

Hi,

* david@...g.hm <david@...g.hm> [2009-06-05 12:15:27-0700]:
> 
> On Fri, 5 Jun 2009, Alexander Clouter wrote:
> 
> > * david@...g.hm <david@...g.hm> [2009-06-04 16:19:56-0700]:
> > > 
> > > On Thu, 4 Jun 2009, Alexander Clouter wrote:
> > > >
> > > > It's dead easy to transmit and receive multicast traffic, broadcasting
> > > > network traffic is so 1980's :)
> > > 
> > > there is only a difference between multicast and broadcast traffic if you
> > > are spanning subnets.
> > > 
> > Well yes and no.  Broadcast traffic is *always* handled by the kernel as
> > only the kernel can tell if it is interested in it or not.  With
> > multicast the NIC is configured to only pass particular
> > Ethernet multicast packets up to the kernel.
> > 
> > By using broadcast traffic the load (okay, hardly a big problem
> > now-a-days) hits *all* the workstations on the subnet, with multicast,
> > only those interested in the traffic receive it.
> 
> true, but only for some NICs, and even those tend to have a fairly small  
> number of slots for the filters. past these limits the OS handles it all  
> just like broadcasts.
> 
I *think* only the early ones have a naff non-hashing based to filter 
multicast flows, could be wrong though.

Either way, as a packet pusher by day, I dream of the venduh's 
discovering that multicast can be used for device discovery rather than 
expecting everything to be on the same subnet :-/

In this day and age, using broadcast to do a job is just plain lazy and 
braindead.

Cheers

-- 
Alexander Clouter
.sigmonster says: Misuse may cause suffocation.
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