Re: 3gpp-analysis: IMS/SIP transition [RE: NAT-PT Applicabilty for 3GPP]

[Pekka Savola <pekkas@netcore.fi>]

On Mon, 17 Nov 2003, Suresh Satapati wrote:
> > Yes, but then again, you don't need DNS-ALG in the v4<->v4 NAT, because
> > the destination address families are the same.  On the other hand, you
> 
> I am afraid you are *wrong*.
> 
> DNS-ALG is not used *merely* for translation between address families.
> DNS-ALG is used to translate addresses contained in PTR queries and any addresses
> in DNS responses (like Answer, Additional RRs). The translation could be
> be replacing a private (rfc 1918) address w/ a public address.

Again, it is not required.  Many NAT boxes do implement this, but many 
others do not.  IPv4 NAT is fully functional without a DNS ALG.
 
> This has been extended to v6<->v4, where an IPv6 address is being
> replaced w/ an IPv4 one.

Right, but you cannot implement NAT-PT without DNS-ALG, or something to
replace the functionality (whereas with v4 NAT, there is no need for the
functionality).
 
> > Instead, we should defer the problem to a SIP working group (SIPPING?) to
> > figure out.. because *they* will be using SIP for interaction, and they
> > know best which kind of solution they'd need (whether based on NAT-PT or
> 
> No concerns on defering the problem to SIP folks, as long as we agree what
> the problem is. If the problem is figuring out the bindings during SIP
> signalling through an external mechanism, then yes I agree. That is all to
> the problem.
> 
> Defining a translator that uses those bindings to do header translation
> has already been defined in RFC2766. SIP wg. should not invent another
> one.

I'm not sure actually what the problem is.  All it is that folks think 
that an optional mechanism for v6-only SIP <-> IPv4 SIP should be 
specified.  I don't personally care much for the details, but the SIP 
folks probably know better which kind of tool might solve the problem.  If 
it's sufficiently close to NAT-PT, why not reuse parts of it and specify 
something to create the mappings; if not, maybe it's worth doing something 
else.  I just don't think this WG is the right place to define that.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings