Subject: Re: [mobile-ip] Mipv6 issue #182: Configured care-of addresses

From: Charlie Perkins <[email-masked]>
Date: Thu, 05 Dec 2002 07:51:12 -0800

Hello Thomas,

I can explain why one might want this.  If a mobile device
roams to a network (such as CDPD) where it will always
get the same IP address, it might wish to use that IP address
as its care-of address whenever it moves into that network.
This has been done for IPv4 networks (although not by me).
If you need to know details about:
   >    ....        how the device knows when it is connected to the
   > specific foreign link where it is allowed to use a particular address,
   > as opposed to some random link where that address would not work....
I can try to get them for you.

Regards,
Charlie P.

Jari Arkko wrote:

> Another issue from your long e-mail. You wrote:
>
>  > > In some cases, a mobile node may already know a (constant) IPv6
>  > > address that has been assigned to it for its use only while
>  > > visiting a specific foreign link.  For example, a mobile node may be
>  > > statically configured with an IPv6 address assigned by the system
>  > > administrator of some foreign link, for its use while visiting that
>  > > link. If so, rather than using Address Autoconfiguration to form a
>  > > new care-of address using this subnet prefix, the mobile node MAY use
>  > > its own pre-assigned address as its care-of address on this link.
>  >
>  > So, explain to me how the device knows when it is connected to the
>  > specific foreign link where it is allowed to use a particular address,
>  > as opposed to some random link where that address would not work....
>
> Perhaps it detects this from the RA that it hears. However,
> I'm not too happy with this function myself. Is there a specific
> reason why this is needed in some environment? Aren't regular
> IPv6 mechanisms sufficient? Is this in the spec for optimization
> reasons? Wouldn't it be better to work on optimistic DAD and improved
> beacons or other schemes instead, given that the configuration-based
> approach doesn't appear to be a very scalable solution in the first
> place.
>
> My proposal is to remove this feature and the paragraph above.
>
> Jari

---

From: "Ed Remmell" <[email-masked]>
Date: Thu, 5 Dec 2002 08:59:40 -0700

Charlie -

Good point. I actually implemented MN protocols for CDPD way back when for a
commercial product (Cincinnati Microwave MC-Dart). BTW, CDPD is being
discontinued (finally). It lasted awhile, considering the effective
throughput is no more than 14.4K baud even with data compression.

The CDPD mobile's NEI (IP address) is pre-configured by the service provider
in the MN. It never changes. It can be used on any AMPS cellular link
supporting CDPD, provided that link belongs to that service provider. It
could possibly even be used on CDPD links that don't belong to that service
provider, provided that there is some type of agreement in place between
service providers allowing that operation (I'd expect there would be a
roaming charge involved).

CDPD is kind of like a MAP as far as how it implements routing to the MN -
but this routing is done at the link-layer, not at the IP layer, so the MN
never uses a CoA when it moves, it just continues using its same home
address regardless of what CDPD network it is operating on. When the MN
moves to a new CDPD network, the MD-IS (i.e. the CDPD-aware router that
connects to the Internet, kind of like a HA because the MN must register its
home address with it) is notified of that move because the MN detects (via a
change in the area color code broadcast by the base station at the CDPD MAC
layer) that it is operating on a different foreign network (served by a
different MD-IS), it registers its NEI with that new foreign MD-IS. The
foreign MD-IS communicates with the home MD-IS to authenticate the MN
registration. The home MD-IS continues to intercept packets sent to the MN's
home address, and routes them (encapsulated in CLNP, I believe) to the
foreign MD-IS so that they can be delivered to the MN on the foreign
network.

One other interesting but slightly off-topic detail: whenever the MN changes
the link it is operating on, it sends a special link-layer frame (a polling
HDLC Receive Ready frame) to "ping" the base station (which may have
changed) at the link-layer. This is very important, because that information
goes all the way back to the serving MD-IS (i.e. the home MD-IS when the MN
is at home, or the foreign MD-IS when it isn't) to let the serving MD-IS
know what link and base station the MN is currently operating on so that it
can correctly route packets to the MN.

Thanks.
- Ed Remmell
Elmic Systems, USA
http://www.elmic.com

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Charlie Perkins
> Sent: Thursday, December 05, 2002 8:51 AM
> To: Jari Arkko
> Cc: Thomas Narten; Mobile IPv6 mailling list
> Subject: Re: [mobile-ip] Mipv6 issue #182: Configured care-of addresses
>
>
> Hello Thomas,
>

---

From: Jari Arkko <[email-masked]>
Date: Thu, 05 Dec 2002 22:29:23 +0200

> This has been done for IPv4 networks (although not by me).

This could be a valid scenario. However, this sounds awful lot
like the task for an IPv6 over Foo document and not the Mobile
IPv6 base specification.

Can I interpret "might want" and "has been done for IPv4" as
an indication that there is no urgent, burning need to do this
for any particular system? If not, I think we should just remove
the paragraph and let IPv6 over CDPD++ or whatever deal with it
later.

Jari

---

From: Charlie Perkins <[email-masked]>
Date: Thu, 05 Dec 2002 13:45:50 -0800

Hello Jari,

That's fine with me, as long as there is no language
that prohibits such uses.

Regards,
Charlie P.