Subject: [pcp] The parity bit in PORT_SET

From: Jean-Philippe Dionne <[email-masked]>
Date: Thu, 14 Mar 2013 16:43:28 -0400

Hi,

I do not think the parity bit is useful in the PORT_SET option.  pcp
clients that will use PORT_SET and doesn't know if they need parity or
not, will simply always set this bit to 1.

The parity bit can be removed from the PORT_SET option if we requires
the NAT to preserve mapping for any PCP request (or by being more
conservative, request with PORT_SET option only).

Jean-Philippe

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From: <[email-masked]>
Date: Fri, 15 Mar 2013 08:16:11 +0100

Dear Jean-Philippe,

It is not harmful to always set the bit to 1. The server can honor it or ignore it just like the suggested port set size.
An application wanting this will insert also a PREFERE_FAILURE option.

Cheers,
Med

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>part de Jean-Philippe Dionne
>Envoyé : jeudi 14 mars 2013 21:43
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>Objet : [pcp] The parity bit in PORT_SET
>
>Hi,
>
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---

From: Jean-Philippe Dionne <[email-masked]>
Date: Fri, 15 Mar 2013 09:56:44 -0400

> An application wanting this will insert also a PREFERE_FAILURE option.

Yes it is not harmful and I think that it is safer to always set it to
1.  If the PCP client is a deamon watching for listen() request, it
might not know that the application needs port parity.  For safety,
it'll always set the parity bit to 1.

For any MAP-PORT_SET request, we could have the requirement that parity
is always preserved.   I'm wondering if it is worth adding an additional
field for parity.  This parity bit would also have to appear as an
additional parameter in the PCP API that a SIP application would use.

If a nat does not support parity preservation, then the pcp client can
simply discover the lack of support by looking at the internal and
external port parity of the pcp response.

Cheers
Jean-Philippe