Subject: [dhcwg] RE: [Mip4] draft-ietf-mip4-gen-ext-03.txt

From: "Chowdhury, Kuntal" <[email-masked]>
Date: Thu, 2 Aug 2007 19:00:17 -0400

Hi Pete,

I think the source of the confusion is the use of DHCP options. The
initial version of this I-D did not propose to use DHCP options at all.
The proposal contained a few possible host config parameters that we
would have defined. However, someone saw the light, and suggested that
instead of redesigning the host config options from scratch, why not we
used the options and the format of the options carrying config info as
defined in DHCP. It made sense; hence we decided to accept that
approach.

Now, I see that people are mixing the use of DHCP protocol with MIP4
host config options. I think this is a digression that we should avoid.
We need to understand the scope of the I-D. It does not rule out other
ways to do host configuration when the MN is using MIP4. It defines _a_
way that is Mobile IP specific. It is also the most efficient one from
the number of round trips point of view.

When you say that running DHCP inside MIP4 tunnel allows for a single
protocol to be used whether the MN is at home or visiting, I have a
question. How is it possible for the MN to fetch config info from the
visited network when RT is negotiated and enforced at the FA? 

BTW, the approach specified in the draft-ietf-mip4-gen-ext-03.txt allows
the use of a single protocol i.e. MIP4 to be used to fetch config info
from home and visited networks, not to mention with fewer number of
messages.

Another issue that we need to think about the use of DHCP inside MIP4
tunnel is security. We cannot prohibit the MN to run DHCPINFORM only,
right? The MN may start doing IP address config (lease and release). How
to secure these DHCP messages? If we intend to only allow the MN to send
DHCPINFORM, how do we prevent it from sending other DHCP messages?

AFAIK, RFC 3118 is not widely implemented and used. Even if it is, we
can't expect the MIP4 implementations to start implementing RFC 3118
just to get a few config info from the home domain.

Regards,
Kuntal

> -----Original Message-----
> From: McCann Peter-A001034 [mailto:[email-masked]]
> Sent: Tuesday, July 31, 2007 9:01 AM
> To: [email-masked]; [email-masked]
> Subject: [Mip4] draft-ietf-mip4-gen-ext-03.txt
> 
> A question has arisen during the last call for
> draft-ietf-mip4-gen-ext-03.txt.
> 
> The draft includes the following text:
> 
>     There are mechanisms
>     such as DHCP for the mobile node to configure information from the
>     foreign network, but not from the home network when the mobile
node
>     is not attached to the home network.
> 
> However, this may not be strictly true.  In particular,
> it might be possible to use a DHCPINFORM message through
> the tunnel that was established with Mobile IP, thus eliminating
> the need to encode DHCP options inside Mobile IP messages.
> This would allow for a single configuration protocol to be
> used whether the MN is at home or visiting.
> 
> I think we may have touched on this question during our last
> chartering discussion but we might not have explored all the
> ramifications.  Please, if you have an opinion either way
> express it now and give some background as to why you think so.
> It is possible that we might turn this draft into a BCP-like
> document for how to configure and run DHCP over the tunnel
> to the home network.
> 
> -Pete
> 
> 
> --
> Mip4 mailing list: [email-masked]
>     Web interface: https://www1.ietf.org/mailman/listinfo/mip4
>      Charter page: http://www.ietf.org/html.charters/mip4-charter.html
> Supplemental site: http://www.mip4.org/

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---

From: Ralph Droms <[email-masked]>
Date: Thu, 30 Aug 2007 08:51:12 -0400

Why is the use of DHCP over MIP4 a digression?  You mentioned:

* more messages
* security

Sounds to me like these issues would be worth exploring if they  
haven't been explored already.

- Ralph