Subject: RE: [Mip6] MN's address as seen by HA is not its CoA but NAT's address (when NAT)

From: "Zhang, Qiang [NTK]" <[email-masked]>
Date: Tue, 28 Mar 2006 09:18:16 -0600

Alex,

In an IPv4 NAT Traversal scenario, a HA that supports the NAT traversal
really use the public side of IP (translation of the MN's private COA)
as the MN's effective COA.. It is probably just a terminology tweak with
assumptions. 

I wonder what happened to the MIPv4 NAT traversal drafts, at least the
original text can refer to some work done before, such as
http://www3.ietf.org/proceedings/03mar/I-D/draft-ietf-mobileip-nat-trave
rsal-07.txt

Qiang
-----Original Message-----
From: Alexandru Petrescu [mailto:[email-masked]] 
Sent: Monday, March 27, 2006 3:59 PM
To: [email-masked]
Subject: [Mip6] MN's address as seen by HA is not its CoA but NAT's
address (when NAT)

I am not sure whether this has already been raised or whether it's a
terminology comprehension issue on my side.

I assume that when MN connects to a v4 access network behind a NAT its
10.x.x.x address is its "v4 CoA" and the publicly routable address used
by NAT after translation is not MN's "CoA".  Maybe another term for this
latter address could be useful.

Thus, section 2.3.2.1 "Visited network supports IPv4 only (private
addresses" wrongly states that
> Hence, all packets addressed to the mobile node's home address(es)
> (IPv4 or IPv6) will be encapsulated in UDP then encapsulated in an
> IPv4 header that includes the home agent's IPv4 address in the source

> address field and the mobile node's IPv4 care- of address in the
> destination address field.    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The destination address of the IPv4 UDP header should be that NAT's
public address (and not MN's v4 CoA).  Moreover, and of utmost
importance, the UDP dst port number of the packet sent by the HA to MN
should be exactly the src port number of the UDPv4 packets received from
NAT (translated by it from MN's CoA).

Alex

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---

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 28 Mar 2006 18:01:07 +0200

Zhang, Qiang [NTK] wrote:
> Alex,
> 
> In an IPv4 NAT Traversal scenario, a HA that supports the NAT 
> traversal really use the public side of IP (translation of the MN's 
> private COA) as the MN's effective COA.. It is probably just a 
> terminology tweak with assumptions.

Yes, I assume so too.  But the section 2.3.2.1 "Visited network supports
IPv4 only (private addresses)" contains:
>> IPv4 header that includes the home agent's IPv4 address in the 
>> source address field and the mobile node's IPv4 care- of address in
>> the destination address field.    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

which should be corrected.

> I wonder what happened to the MIPv4 NAT traversal drafts, at least 
> the original text can refer to some work done before, such as 

Became an RFC?

Alex

---

From: Henrik Levkowetz <[email-masked]>
Date: Tue, 28 Mar 2006 18:43:50 +0200

Alex, Qiang,

  As Qiang says, the effective CoA address is the NATted address. The text
in 2.3.2.1 is correct but maybe not clear under the circumstances, so we
could clarify this.  And you're right regarding the Port number, Alex, but
this is no different from any other UDP responses, which go back to the
originating port.

Qiang, Regarding the MIPv4 NAT traversal document, it was published as RFC 3519
in April 2003.

Regards,

	Henrik

---

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 28 Mar 2006 18:47:26 +0200

Henrik Levkowetz wrote:
> And you're right regarding the Port number, Alex, but this is no
> different from any other UDP responses, which go back to the 
> originating port.

Yes that is right, as usual goes back to src port of incoming packet.
Worth mentioning though IMHO.  That will bring in the assumption of
stability of that originating port on the NAT side.

Alex