[114474] in North American Network Operators' Group
Re: two interfaces one subnet
daemon@ATHENA.MIT.EDU (Per Heldal)
Tue May 12 04:30:49 2009
Date: Tue, 12 May 2009 10:30:18 +0200
From: Per Heldal <heldal@eml.cc>
To: David Devereaux-Weber <ddevereauxweber@gmail.com>
In-Reply-To: <f2675b350905111422k30de64caub1bce3630ac1e8df@mail.gmail.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
David Devereaux-Weber wrote:
>
> I work with iHDTV <http://ihdtv.org>, a project that sends uncompressed high
> definition television (1.5 Gbps) as UDP over two 1 Gbps interfaces. If both
> interfaces are on the same subnet, the OS sees the same router (gateway)
> address on both interfaces, and the results are sub-optimal ... around 50%
> packet loss.
>
Check closes and you may discover that the loss isn't on the path
host->router, but on the reverse.
Some hosts/interfaces are optimised for L2 link-aggregation, in which
case they by default present the same MAC (host MAC-address) on multiple
interfaces. Those will fail when configured with separate IP-addresses
on the same VLAN/subnet. L2 switches that support link-aggregation will
try to spread the traffic across the available ports on one VLAN on
which it sees the same MAC. 2 ports gives 50% loss, 3 ports 67% and so
on. Most host interfaces will not pick up IP-packets which destination
doesn't match it's assigned address.
//per
