Re: [v4v6interim] Potential interoperability issue

On 2008-10-03 06:51, james woodyatt wrote:
> On Oct 2, 2008, at 10:31, Fred Baker wrote:
>>
>> Sitting in your discussion of applications that may have issues
>> through a translator. In the chat room, I asked:
>>
>>> Dumb question from personal ignorance. SMTP opens with a HELO or EHLO
>>> that has the IP address of the MTA in it. Does SMTP treat that as a
>>> character string, or does it interpret the address? If it interprets
>>> the address, it may have the same issue as FTP in a 6to4 environment
>>
>> and James Woodyatt replied
>>
>>> Some things interpret it as an address, e.g. rule processing engines
>>> for deciding whether to require TLS. Or authentication.
> 
> The EHLO message has a domain name.  In SMTP, the Domain grammar
> production includes a special case allowing for an IP address literal
> instead of a FQDN.  This domain name in the EHLO message is sometimes
> used to make decisions about TLS and AUTH requirements.  So, too, can
> the IP address of the connecting client be used for such decisions.
> 
> Whether an ALG is required to cope with this is a question I'm not
> prepared to answer.
> 
>> That either calls for an ALG or appropriate code in the servers that
>> can deal with an <> address even when the server doesn't have such an
>> address. The simplest resolution might be to have the MTA have a leg
>> in the IPv6 world and one in the IPv4 world.
> 
> I would agree that this is the simplest way to handle SMTP servers.
> 

Yes. Incidentally, SMTP is listed in RFC 3027 among the "Protocols that
can work with the aid of an ALG", but the discussion seems rather
brief to me.

    Brian
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