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

From: kempf <[email-masked]>
Date: Thu, 12 Apr 2001 19:26:57 -0700 (PDT)

Hi Luca,

OK, please ignore the previous reply, with garbage, my keyboard started
going crazy in the middle, will my email woes ever subside...

Anyway ...

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

DHCP was originally designed to configure address information, it
was only due to the lack of a standardized service discovery mechanism
that everything else got dumped in. Now, there are far better ways
of doing configuration of service discovery information (LDAP, SLP, DNS SRV RR). 
And the only reason DHCP was needed to do address configuration was because
IPv4 doesn't have autoaddress config nor router-advertised subnet
prefixes.

>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.
>

The fact of the matter is that mobile IP is currently deployed in
3GPP2 networks without DHCP & there is no DHCP on 3GPP2 phones or
the brand new Sprint PCS modems I've just started seeing advertised
in the New York Times. They use PPP and Radius to configure the 
address information. So from the point of view of the system
administrators and users who are using mobile IP *today* this is a very big
change indeed, despite what enterprise network administrators think.

Not every IP node is connected to an enterprise network, in fact,
in the future, nodes homed and connected to enterprise networks
may be in the minority.

>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.
>

I disagree. I would rather see something that builds on the current
infrastructure, that won't involve 3GPP2 having to tear up their
current infrastructure. If DHCP is put in, people will think the
problem is solved.

>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.
>

Sure, it will work just fine when the mobile node goes home. The
mobile node has mobile IP with address and routability configuration
(see below for more on this), uses that to get what it needs from the 
home agent, home agent uses DHCP out the back end (or Radius/PPP
or Diameter if it is in a WAN situation) to get the address/routability
information, gives it to the mobile, mobile node uses service discovery
to find services.

Now perhaps some perspective (especially for PhilN's benefit). 

I think we are talking about three different kinds of configuration 
information supplied by DHCP:

1) Information that is required for basic routing of packets to the host.
On IPv4, this consists of the IP address, the subnet mask, and perhaps
the gateway router. On IPv6, this consists of the subnet prefix, perhaps
an IP address if one is assigned, the router can be discovered.

2) Borderline service discovery information that would be difficult
to bootstrap. This is primarily DNS.

3) Service discovery information such as printers, LDAP servers and
the like.

Now, I think we all agree that mobile IP shouldn't be delivering 3) and
I think that there are today better ways of doing 3) as I discussed
above. If DHCP is available, by all means use it, but it isn't
available on today's mobile IP networks and I don't think 3) is
enough justification to introduce DHCP.

As far as 1) is concerned, what's the problem with having mobile
IP deliver basic routability information? In IPv6, most of this
information is delivered by router advertisements or by address
autoconfig, which is part of the routing protocol. Since mobile
IP is concerned with routing, I think it should be involved in
distributing routing configuration.

That leaves only 2). My understanding is that the DNSng group is
working on ways to find a DNS server in IPv6 that don't require getting
it from DHCP. So that leaves one single piece of information in
IPv4 that doesn't fit in. This could be distributed by AAA or
even we could make one tiny exception and do it by mobile IP as well
(just as DHCP is used in enterprise networks  for all kinds of 
service discovery information), or we could come up with a protocol
like IPv6 is.

Bottom line for me is that DHCP is not used in mobile IP networks
today, Radius/PPP is. I would rather see us building on that
infrastructure than introducing new requirements for what the mobile
node has to support. And I don't buy the argument that we can do
it as an option. Once it is there, people will think they have
to support it. 

		jak

---

From: Luca Salgarelli <[email-masked]>
Date: Fri, 13 Apr 2001 09:49:30 -0400

Hi James.

> DHCP was originally designed to configure address information, it was
> only due to the lack of a standardized service discovery mechanism that
> everything else got dumped in. 

We can debate about this forever, but that does not mean that the DHCP
specs we have today for IPv4 don't do a good job in distributing
configuration information, and not only addresses. Otherwise how do you
justify its widespread use?

> >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.
> >
> 
> The fact of the matter is that mobile IP is currently deployed in 3GPP2
> networks without DHCP & there is no DHCP on 3GPP2 phones or the brand new
> Sprint PCS modems I've just started seeing advertised in the New York
> Times. They use PPP and Radius to configure the address information. So
> from the point of view of the system administrators and users who are
> using mobile IP *today* this is a very big change indeed, despite what
> enterprise network administrators think.

I agree on the 3GPP2 comment, and I also agree on the fact that 3GPP2 today
is the major utilizer of Mobile-IP. But I disagree with respect to a couple
of points:

1) Making Mobile-IP able to gracefully support DHCP does not mean that
every Mobile-IP network *MUST* deploy and use DHCP. It only means that who
*wants* to (e.g. corporate networks) will be able to do it.

2) The fact that today's 3GPP2 clients use PPP and RADIUS to configure
their addresses does not mean that they won't need something else to
configure their (corporate?) home addresses in some scenarios.

Again, I would like to stress point (1), which I pointed out already in my
previous e-mails: we are not talking about a mechanism that HAS TO be
deployed. We are talking about leaving the possibility open for ISP's that
want to use it.

> >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.
> >
> 
> infrastructure, that won't involve 3GPP2 having to tear up their current
> infrastructure. If DHCP is put in, people will think the problem is
> solved.

I disagree with you once more: we are not saying that DHCP must be put in.
If people want to use something else, fine! We don't want to mandate the
use of DHCP.

> Sure, it will work just fine when the mobile node goes home. The mobile
> node has mobile IP with address and routability configuration (see below
> for more on this), uses that to get what it needs from the home agent,
> home agent uses DHCP out the back end (or Radius/PPP or Diameter if it is
> in a WAN situation) to get the address/routability information, gives it
> to the mobile, mobile node uses service discovery to find services.

I don't know if you read previous notes from Sandy's about this (I think it
was a response to Pat), but this scheme won't just be so simple if the
mobile goes home. Simply put, if the HA is responsible for a pool of
addresses, the client will have to keep re-registering even if it is at
home in order to defend the address.

Luca