Subject: [MOBILE-IP] A practical question...

From: Matteo Berioli <[email-masked]>
Date: Mon, 9 Oct 2000 16:48:47 +0200

I would appreciate very much any explanation.
It's a little bit long, but I hope fast and clear!
Thank you.

PROBLEM: Let' s assume we have a Mobile Router, to which a Mobile Host
attaches. We know how the matters work with IPv4 and Mobile IP (see RFC
2002 par: 4.5 page 61-62). The problem is here that we have a double
re-direction of each packet directed to the Mobile Host. As a matter of
fact, each packet has to pass through the Home Agent of the Mobile Host
and then through the Home Agent of the Mobile Router.
Let's assume, now, that the mobile network is an IPv6 network. In IPv6
could be this double re-direction avoided?

I guess:

1° possibility
A pool of IPv6 addresses is assigned to the Mobile Router when it
desires to connect to the Internet; so the Mobile Router can assigned an
its own Care-of Address to each Mobile Host asking for one. This allows
the Mobile Host to inform by itself its Correspondent Nodes and its Home
Agent of this new Care-of Address, and this avoids the double
re-direction...

2° possibility
A single IPv4 address is assigned to the Mobile Router as its Care-of
Address, because, for example, the Edge Router to which the Mobile
Router attaches doesn't support IPv6. Now the problem comes!
It could be solved in this way (I wonder if it is possible and
realistic...):
when a Mobile Host attaches to the Mobile Router, it asks to the DHCP
server, which is in the Mobile Router, for a Care-of Address, and sends
its Home Address to it;
the Mobile Router could use Stateful Address Autoconfiguration (setting
M=1 in the Router Advertisement packets), and it could oblige all the
hosts in the mobile network, to acquire the same Care-of Address, that
is the one it got from the Edge Router!!
So all the hosts, both fixed and mobile hosts, share one Care-of
Address; but they don't care about this, because the Mobile Router set
M=1 in the Router Advertisement packets, so avoiding Stateless Address
Autoconfiguration and Duplicate Address Detection.
So each host on the mobile network can inform by itself its
Correspondent Nodes and its Home Agent of this new Care-of Address.
Now when a packet arrives to the Mobile Router, obviously it will be
encapsulated in an IPv4 packet (see figure in the attachment), so first
of all the Mobile Router has to decapsulate it.
Then if the packet comes from a Correspondent Node it will have, as
Destination IP Address, the Care-of Address of the Mobile Router and in
the Routing Header it will have the Home Address of the Mobile Host that
is on the mobile network, and with which the Correspondent Node is
communicating.
The Mobile Router knows the Home Addresses of the Mobile Hosts it has in
charge and knows to which link-layer addresses they are related; so the
Mobile Router has to recognize this address in the Routing Header and it
has to forward the packet directly in the local network to the Mobile
Host.
If the packet comes from the Home Agent of one Mobile Host that is
attached to the mobile network, the matters are similar. The only
difference is that the packet will be encapsulated in an IPv6 packet,
too; therefore the Mobile Router has to decapsulate again the packet,
again it has to recognize the Home Address of one Mobile Host it has in
charge, and it has to forward the packet to it through its link-layer
address.

Probably the picture I made can clarify the problem.

1° possibility:

2° possibility:

Thanks again to anyone will answer.

Matteo Berioli

---

From: Thierry Ernst <[email-masked]>
Date: Mon, 9 Oct 2000 17:57:08 +0200

Matteo Berioli wrote:
> attaches. We know how the matters work with IPv4 and Mobile IP (see
> RFC 2002 par: 4.5 page 61-62). The problem is here that we have a
> double re-direction of each packet directed to the Mobile Host. As a
> matter of fact, each packet has to pass through the Home Agent of the
> Mobile Host and then through the Home Agent of the Mobile Router.

Hi Matteo,

I have also been doing some thinking about mobile networks.  This issue
has not really been addressed nor even raised though there are many
interesting problems to be dealt with.   

At the time being, Mobile IPv6 does not support mobile networks at all.  
The Home Agent of the Mobile Router is unable to redirect packets sent
to a node attached to the Mobile Router (call it MNN - Mobile Network
Node), and no optimal routing is possible between the CN and the MNN.   
See my Internet Draft for the problem description on the IETF web site
or on my web page:
http://www.inrialpes.fr/planete/people/ernst/Documents/draft-ernst-mobileip-v6-network

> desires to connect to the Internet; so the Mobile Router can assigned
> an its own Care-of Address to each Mobile Host asking for one. This
> allows the Mobile Host to inform by itself its Correspondent Nodes and
> its Home Agent of this new Care-of Address, and this avoids the double
> re-direction...

You need a protocol to enquire and distribute the care-of address
between the Mobile Host and the Mobile Router.   

> Router attaches doesn't support IPv6. Now the problem comes!

Are you dealing with Mobile IPv4 or with Mobile IPv6 ?  

> server, which is in the Mobile Router, for a Care-of Address, and
> sends its Home Address to it;

The DHCP server is not necessarily on the Mobile Router.   The Mobile
Network may be composed of several routers (i.e. subnets).  What if the
Mobile Host does not attach directly to the Mobile Router ?

> the Mobile Router could use Stateful Address Autoconfiguration
> (setting M=1 in the Router Advertisement packets), and it could oblige
> all the hosts in the mobile network, to acquire the same Care-of
> Address, that is the one it got from the Edge Router!!

> Correspondent Nodes and its Home Agent of this new Care-of Address.

As a result, all hosts have to take active part in the mobility
management of the mobile router.     I don't find this solution
reasonable.   My solution is that all the mobility management is done by
the Mobile Router (MR) ; the MR advertises its CoA together with its
prefix asking all CNs of nodes located in the mobile network to use the
MR's CoA when they want to send a packet holding a destination address
matching the prefix of the MR.

> encapsulated in an IPv4 packet (see figure in the attachment), so
> first of all the Mobile Router has to decapsulate it.
> Destination IP Address, the Care-of Address of the Mobile Router and
> in the Routing Header it will have the Home Address of the Mobile Host
> that is on the mobile network, and with which the Correspondent Node
> is communicating.

> The Mobile Router knows the Home Addresses of the Mobile Hosts it has
> in charge and knows to which link-layer addresses they are related; so
> the Mobile Router has to recognize this address in the Routing Header
> and it has to forward the packet directly in the local network to the
> Mobile Host.

Same comment as before, if the MN does not attach directly to the MR.

Cheers,
Thierry.

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