Re: [v4v6interim] Potential interoperability issue

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.

--
james woodyatt <jhw@apple.com>
member of technical staff, communications engineering

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