Internet DRAFT - draft-mrosenau-email-ipv4-to-6
draft-mrosenau-email-ipv4-to-6
Network Working Group M. Rosenau
Internet-Draft Hobbyist developer
Expires: July 18, 2013 January 14, 2013
Email transfer in the IPv6 introduction phase
draft-mrosenau-email-ipv4-to-6-00
Abstract
During the introduction phase of IPv6 (as of Jan 2013) many existing
mail servers are not able to do IPv6 communication, yet. However new
networks will be assigned IPv6 addresses only so new mail servers
will not be able to do IPv4 communication.
This document proposes the installation of special servers that are
able to route mail between IPv4-only and IPv6-only mail servers to
solve this problem.
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This Internet-Draft will expire on July 18, 2013.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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1. Background
As of the end 2012 IPv4 addresses are no longer available to
companies. For this reason new mail servers (especially mail servers
of companies that do not have IPv4 addresses, yet) are IPv6-only.
The introcuction of IPv6 on existing mail servers, however, is often
not done right now.
RFC 3974 proposes that every mail server should have an IPv4 address
even if it is able to do IPv6. However this is no longer possible
due to the depletion of IPv4 addresses.
For this reason it may be impossible to send an electronic mail from
a domain that has an IPv4-only server to a domain using an IPv6-only
server and vice versa.
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2. Implementation
2.1. Tunnel servers
This document proposes the installation of IPv4-to-IPv6 translation
servers to manage the problem. Such a server would work the
following way:
o Accept incoming SMTP connections on IPv4 AND IPv6
o For each mail "received" simply forward the received mail to the
SMTP server that is really responsible for the destination address
In our example such servers have the addresses 192.0.1.30 and
192.0.1.31. The DNS configuration may look like this:
example.org. IN MX 1 mx1.example.org.
example.com. IN MX 1 mx1.example.com.
ip4only.example. IN MX 1 mx1.ip4only.example.
mail-tunnel.example. IN AAAA 2001:db8:ffff::1
mail-tunnel.example. IN AAAA 2001:db8:ffff::2
mail-tunnel.example. IN A 192.0.1.30
mail-tunnel.example. IN A 192.0.1.31
mx1.example.org. IN AAAA 2001:db8:ffff::1:1
mx1.example.org. IN A 192.0.1.30
mx1.example.org. IN A 192.0.1.31
mx1.example.com. IN AAAA 2001:db8:ffff::2:1
mx1.example.com. IN A 192.0.1.30
mx1.example.com. IN A 192.0.1.31
mx1.ip4only.example. IN A 192.0.2.1
Note that mx1.example.com and mx1.example.org are different (!)
servers. However the IPv4 address in the DNS configuration is the
same. The DNS query for their IPv4 address will result in the IPv4
address of the server "mail-tunnel.example" because they do not
support IPv4.
2.2. IPv4-to-IPv6 mail transport
Scenario: An Email is sent from example@ip4only.example to
example@example.com.
The mail server of the domain ip4only.example will now query the IPv4
address of mx1.example.com. The DNS server will return the address
192.0.1.30 which is in fact the address of the tunnel server.
The mail is now delivered to the tunnel server, that then forwards
the mail to the actual mail server.
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2.3. IPv6-to-IPv4 mail transport
Scenario: An Email is sent from example@example.com to
example@ipv4only.example.
The mail server of the domain example.com will now query the IPv6
address of mx1.ipv4only.example. The DNS server will return no
result.
In this case the mail server's implementation must be done in a way
to allow transmission to IPv4-only domains: It must detect this case
and directly connect the tunnel server or use other tunneling
mechanisms that allow connecting the IPv4 mail server using a TCP
connection from an IPv6-only network directly (like NAT64).
Note: If an IPv6 mail server has access to NAT64 and DNS64 it can
send mail directly to an IPv4 mail server
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Author's Address
Martin D. J. Rosenau
Hobbyist developer
Email: martin@rosenau-ka.de
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