Subject: [mobile-ip] MIP NAT Traversal (draft-ietf-mobileip-nat-traversal-00.txt)

From: pradeep <[email-masked]>
Date: Tue, 26 Feb 2002 00:46:53 -0600

Hi,

I am working on implementation of NAT Traversal for MIP 
(draft-ietf-mobileip-nat-traversal-00.txt) over Linux. I will be very
        glad, if you could clarify the following question:

        In section 4.6 of the above mentioned draft, it's been stated as 
follows:
        "The home agent MUST use a mismatch between source IP address and
        care-of address in the Mobile IP Registration Request message as the
        indication that a mobile node may reside behind a NAT."

        What will be the source IP address value in the IP header of the
        registration request message sent by the mobile node, while it has 
moved
        to a foreign network and using a co-located care of address?

        In RFC 3220, section 3.6.1 it is stated that,

        IP Source Address:
        - When registering on a foreign network with a co-located care-of
        address, the IP source address MUST be the care-of address.
        - Otherwise, if the mobile node does not have a home address, the
        IP source address MUST be 0.0.0.0.
        - In all other circumstances, the IP source address MUST be the
        mobile node's home address.

        This means, when a moible node using co-located care of address wants
        to directly register with the home agent, the source IP address in the 
IP
        header of the registration request will be mobile node's home addres.

        1) How exactly the NAT in foreign network will handle this 
registration
        request packet as the packet's source addreess is set to mobile node's
        home address, which is not known to the NAT? (if the source or
        destination address is not recognized by the NAT, it will not make any
        changes to the packet's source and destination address in the header).
        2)How the mobile node's home agent, will come to know the foreign
        networks' NAT address?
        3)How the mobile node's home agent, will know that the registration
        request packet has passed through the NAT in foreign network?

Thanking You,
Pradeep Natarajan.

---

From: "Henrik Levkowetz" <[email-masked]>
Date: Tue, 26 Feb 2002 08:15:39 +0100

Hi Pradeep,

	I just got this exact question from Karthikeyan Nathillvar, and
> glad, if you could clarify the following question:

Oh, cool!

>  In section 4.6 of the above mentioned draft, it's been stated as follows:
> registration request message sent by the mobile node, while it has moved
> to directly register with the home agent, the source IP address in the IP

Mmm, I think that if you read the first bullet in the quote from RFC 3220
again, you'll find that when a when a mobile node using a co-located care of 
address wants to register with the home agent from a foreign network, the IP
source address MUST be the care-of address. 

However, if the mobile node is not in a foreign network (i.e. is at home)
or is not using a co-located care-of address (i.e. is at home or is using
an FA care-of address), the next 2 bullets hold. 

	Regards,

		Henrik