Subject: Re: [MOBILE-IP] Dynamic Address Assignment in Mobile IP

From: Pete McCann <[email-masked]>
Date: Mon, 10 Apr 2000 17:36:24 -0500

Hi, Vipul,

Vipul Gupta (VG) writes:

> 3) There was a lot of discussion about the proper role of DHCP in a
>    Mobile IP network.  My personal feeling is that it is perfectly
>    fine to use Mobile IP for address assignment, but any other parameters
>    should be configured via DHCP after the registration has completed.
>    This is analagous to the way DHCP would be used over a PPP link,
>    for example.  That way the MN could be registered and have an address
>    in one quick round trip for most cases.

VG>  I agree. As people start using Mobile IP in other scenarios, the mobile
VG>  node will need to acquire additional parameters (e.g. it might need
VG>  an "internal" DNS server when using private addresses) and it makes
VG>  sense to reuse DHCP for this purposes. The PPP WG has already been
VG>  down the path of first trying to add lots of DHCP-like functionality
VG>  to PPP and then deciding on reusing DHCP (through the DHCP inform
VG>  message) as the preferred approach.

Yes.  However, unlike PPP with compulsory tunneling, we must be a
little careful in our treatment of broadcast packets (see my previous
note).

VG>  [Interestingly enough, the IPSRA working group (IPSec for remote access)
VG>  is also going through a similar debate -- reusing DHCP v/s extending
VG>  IKE for negotiating network parameters relevant to the
VG>  "internal network". For some background on why the former is better,
VG>  see draft-ietf-ipsec-dhcp-04.txt.]

I saw Bernard present this draft to the IPSRA WG - it was quite
interesting.  I agree that a lot of the issues are similar but there
is one important difference: with IPSEC remote access, there is an
assumption that the MN first has an address allocated on the visited
network.  We are trying to support cases where this is not true (FA
located COA to support minimal tunnel overhead and v4 address space
usage).  So it is appropriate to assign the private address using
Mobile IP, rather than DHCP as this draft advocates.

-Pete

---

From: "Martin Johnsson (ERA)" <[email-masked]>
Date: Wed, 19 Apr 2000 14:22:15 +0200

Please find my comments inline below.

-----Original Message-----
From: Pete McCann [mailto:[email-masked]]
Sent: den 11 april 2000 00:30
To: [email-masked]
Subject: Re: [MOBILE-IP] Dynamic Address Assignment in Mobile IP

Hi, Martin,

Martin Johnsson (MJ) writes:

MJ> Regarding the use of DHCP in corporate environment, the idea would
MJ> be to have the possibility to configure "everything" from the
MJ> beginning, i.e. both the address of the HA as well as MN's IP
MJ> address corresponding to the home network, and possibly also the
MJ> address corresponding to the visited network. This means that
MJ> tunneling via the HA (And FA) won't begin until you have all this
MJ> configured in the MN.

MJ> We have done this in actual implementation, and it works fine,
MJ> though there is a need to make some modifications in the DHCP
MJ> client when you request the IP addresses for both home + visited.

So are you saying that the MN uses DHCP to acquire both a home and
visited address?  What if the MN powers up on a network that is far
from home?  How do you contact the home network (which might be
another service provider) to allocate an address?  Do you tunnel the
DHCP request back to the home network?  And all this takes place
before the HA-FA tunnel is even set up... I am concerned that
solutions like this will start to look a lot like re-inventing Mobile
IP.

Maybe what you are doing is assuming that the MN always powers up "at
home," i.e., it gets a dynamically allocated HA in the visited
network.  This is OK for some situations, but what about when a user
wants to use an HA situated in a private network, and to use a private
address on that network?  The beauty of the NAI draft is that the
address can be allocated by the home network as part of the Mobile IP
registration, and the MN need not be given any sort of address on the
visited network.

Martin:
Well, as was agreed upon in a previous mail exchange, using NAI for remote access is fine, especially when it will be (eventually) possible to also dynamically configure the HA address located in the private network via DIAMETER.
What I referred to was the possibility to use DHCP within one network (domain of control) to configure IP addresses and HA in the MN. A valid requirement for many private networks today.

Now, if you come to a visited network whose DHCP server doesn't assign for instance IP address for home network and address for HA (most likely you only get a COA, if using colocated COA), the logic should be in the MN to use preconfigured values (e.g. address of HA) and then to use NAI.

Cheers,
   /Martin