Subject: Re: [mobile-ip] dynamic home addressing as a WG item??

From: James Kempf <[email-masked]>
Date: Thu, 12 Apr 2001 15:25:24 -0700 (PDT)

Hi Luca,

>I think I agree with Phil on this. I am not comfortable with the idea of
>coupling a routing protocol with something needed to distribute
>configuration information.
>

But you are comfortable with having an address provisioning mechanism
distribute service discovery and configuration information? Curious.

>I think that a clean separation between the two is needed.
>
>> OK, then what would you suggest? I think extending
>> DHCP to the mobile is just as much of a hack.
>
>I don't see why you consider "extending DHCP" to the mobile a hack:
>Mobile-IP is designed to transparently hide the movements of the client. So
>I don't see why you would see letting DHCP "transparently" run on top of
>the Mobile-IP tunnel a hack.
>
>

I consider it a hack because it involves a lot of mechanism (DHCP relays,
reverse tunneling) that is unnecessary. Besides, there is no requirement
for the home network to use DHCP to configure the mobile node, it
could use something different (LDAP for example). I rather think
the hiding should be done by on the mobile side, so that it does
not have to deal with how the home network configures.

Hmm, is this perhaps the problem? You, Sandy, and maybe Phil view the
mobile node as being an extension of the home network, correct? This
is the traditional mobile IP view. I have rather a different view.
I view the mobile node as mostly away from the home network, not
really bound to it except though routing. So a possible, even likely,
situation is that the mobile node gets a locally assigned home
address every time it comes up in someone's network. As a result,
the mobile node should be getting the configuration information from
where the home address is assigned, and I view it as rather too burdensome
to require every wireless network operator to have to deploy DHCP.

Besides, as I said at the beginning of this thread, I don't see why every mobile 
node in the world has to essentially support two address provisioning 
mechanisms, mobile IP and DHCP. Phil's comments notwidthstanding, mobile
IP does not just do routing, it also does address configuration. We need to find 
out some other way of doing lightweight configuration, since that is all DHCP 
will be used for on the mobile node. 

Maybe what we need is "DHCP lite" that extracts out the configuration
part of DHCP and gets rid of the need for a reverse tunnel for broadcast.

		jak

---

From: Luca Salgarelli <[email-masked]>
Date: Thu, 12 Apr 2001 20:46:27 -0400

Hi James.

> distribute service discovery and configuration information? Curious.

Hmmm, as far as I know, DHCP stands for Dynamic Host *Configuration*
Protocol. It has been designed exactly for distributing configuration
information.

> not have to deal with how the home network configures.

I agree that something different could be used, but the way it is
(very successfully) being done today is through DHCP. Network
administrators just seem to like it a lot, so I think supporting it should
be somthing we should make MIP capable of. If then we want to think at a
better way to do it, it is fine by me.

> to require every wireless network operator to have to deploy DHCP.

I agree, we are probably thinking about two different scenarios.
Nevertheless, I don't think anybody is saying that support for DHCP should
be a MUST for MIP. What I would like to see is some way for MIP to support
it, for the ISP's that think it is needed.

> Besides, as I said at the beginning of this thread, I don't see why every
> mobile node in the world has to essentially support two address
> provisioning mechanisms, mobile IP and DHCP. Phil's comments
> notwidthstanding, mobile IP does not just do routing, it also does
> address configuration. 

Again, that might work in the scenario you described above. It will not
work (very well, at least) in scenarios where the mobile goes home from
time to time, as Sandy pointed out already.

Luca

> We need to find out some other way of doing
> lightweight configuration, since that is all DHCP will be used for on the
> mobile node. 
>