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Re: [Softwires] ALG section in draft-ietf-softwire-dual-stack-lite-06

Mark Townsley <townsley@cisco.com> Wed, 23 February 2011 16:28 UTC

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From: Mark Townsley <townsley@cisco.com>
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Date: Wed, 23 Feb 2011 17:29:40 +0100
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To: Dan Wing <dwing@cisco.com>
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Cc: softwires@ietf.org, draft-ietf-softwire-dual-stack-lite@tools.ietf.org
Subject: Re: [Softwires] ALG section in draft-ietf-softwire-dual-stack-lite-06
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I'd like to see all softwire documents be as silent as possible on specifics of NAT. The essential delta in ds-lite vs. a NAT44 CGN is that the tunnel is embedded within the NAT binding.  I think the softwire documents should explain this, then point to behave for anything else that has to do with operating a CGN. We are the tunneling folks here, the translation folks are down the corridor.

- Mark


On Feb 23, 2011, at 5:19 PM, Dan Wing wrote:

> http://tools.ietf.org/html/draft-ietf-softwire-dual-stack-lite-06 says:
> 
>   8.3. Application Level Gateways (ALG)
> 
>   The AFTR should only perform a minimum number of ALG for the classic
>   applications such as FTP, RTSP/RTP, IPsec and PPTP VPN pass-through
>   and enable the users to use their own ALG on statically or
>   dynamically reserved ports instead.
> 
> Comments:
> 
> * To my knowledge, this would be the first time IETF suggests using an ALG
> in a NAT44 in a standards-track document.
> 
> * Both IPsec and PPTP are protocols, not applications.  IPsec is 50
> (assuming you mean IPsec ESP, which I'm sure is what was intended) and PPTP
> uses protocol 47 (GRE).  Thus, these do not belong in the Application Level
> Gateway section.  Rather, IPsec and PPTP should be moved to the previous
> section (NAT Conformance) which already mentions other protocols like TCP
> and ICMP.
> 
> * There aren't specifications describing an ALG for FTP, RTSP, RTP, IPsec,
> or PPTP VPN.
> 
> * What is "RTSP/RTP"?  Is this trying to say "RTSP, when it is using RTP",
> or is it trying to say "RTSP and other uses of RTP".  Text needs to be
> clarified.
> 
> * IPsec Passthru is pretty common on residential NATs.  However, in a CGN,
> IPsec Passthru is difficult when multiple users connect to the same VPN
> concentrator.  When that concentrator re-keys a session, the incoming IPsec
> SPI changes and there is no simple way to determine which user should
> receive that packet.  There are several workarounds to this problem,
> including just ignoring it.
> 
> -d
> 
> 
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