Subject: RE: [Fecframe] PNAT?

From: "Mark Watson" <[email-masked]>
Date: Wed, 9 Nov 2005 16:18:30 -0500

Caitlin,

The framework itself does not have any requirements with respect to NATs
or NAPTs - we require that the receiver knows the UDP flow definitions
of the flows containing source and repair data and that there is a path
from sender to receiver.

Specific protocols that used the framework would have to address how
they work through NA(P)Ts. I assume the case you refer to below is where
the source and repair flows are identified using different UDP ports and
the traffic attempts to traverse a NAT from the 'outside' to the
'inside'.

In this case, just as the protocol must arrange for a suitable binding
to exist for the source packets, it must also arrange for a suitable
binding to exist for the repair packets - it is the same problem for
both source and repair flows.

If you are thinking of 'retrofitting' the FEC repair flow to an existing
source packet protocol with existing NA(P)T traversal support then I
think you would need to make the repair packets look like part of the
same flow as the source packets from the NA(P)Ts point of view. This is
easy, but the tradeoff is that you have to place some restrictions on
the packet contents. You need to have somewhere in there to distinguish
source from repair packets i.e. you swap some generality for backwards
compatibility.

Regards,

Mark

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Caitlin Bestler
Sent: Wednesday, November 09, 2005 12:57 PM
To: [email-masked]
Subject: [Fecframe] PNAT?

Does the current proposal require that all middleboxes
operate strictly at L3 and below? I don't see how this
scheme would work if there are any middleboxes that
modify the UDP port numbers as part of a PNAT/firewall
function. If the packet had an error it would get
tossed at that point, and there would be no chance
to repair it later.

And doesn't requiring that there me no L4 aware
middleboxes all but require this be IPv6?

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