Subject: Re: [mobile-ip] Mobile Routers support without optimization

From: James Kempf <[email-masked]>
Date: Thu, 16 Aug 2001 12:45:51 -0700 (PDT)

Alex,

>> >You mean that instead of a CoA, a visiting MR would obtain a CoP
>> >(care-of prefix) and renumber its MNN's with it?
>> 
>> I was thinking of the route optimization case, where the MR sends a
>> BU with a prefix. Should the autonomous system of the access network
>> reserve this prefix and should the prefix be advertised via BGP even
>> if there is no MR there?
>
>If by "access network" you mean the foreign network then the prefix in
>BU sent by MR doesn't belong to the foreign net but to the home net,
>so it's not advertised by that BGP right?
>

Sorry for sounding totally clueless, but I'm extrapolating what's
in the BU from what would be in if an MN were to send it. If
an MN sends it, the BU contains the care of address, which is
in the foreign network. Extrapolating, the MR would have
to send a prefix that is in the foreign network. The point of
the BU in the mobile host case is to tell the HA and CN to change
its routing to the new address. The point of the BU for a MR is
presumably to cause a change in the routing tables in subnets
that are corresponding with host behind the MR, including the
home network. That is, of course, if you want to completely
eliminate triange routing.

>If by "access network" you mean the home network then the BGP of the
>AS of that could freely advertise that prefix (a superset of it),
>because even if MR-not-at-home, its prefix would be defended by the HA
>when receiving a BU.
>
>> Seems like an invitation for even more growth in routing tables, but
>> if this isn't done, then I suppose one would have to wait for the
>> updates to propagate before the prefix was visible outside the
>> autonomous system.
>
>All valid argument.
>
>> But now that you mention it, what does a MR having a "home address"
>> mean?  According to Erik's previous definition of a router, a router
>> forwards traffic that is not sent to it. 
>
>I was thinking that MR's home address is like a classical MN's home
>address.  When MR is not at home, all incoming traffic from CN's to
>MNN's, would first go to HA, encapsulated, decapsulated by
>MR-not-at-home and forwarded to MNN.  Thus, the scenario agrees with
>Erik definition of a router: MR-not-at-home would still forward
>traffic not directed to itself.
>

This sounds like MIP + a NAT.

		jak

---

From: Alexandru Petrescu <[email-masked]>
Date: 17 Aug 2001 10:10:35 +0200

James Kempf <[email-masked]> writes:
> Sorry for sounding totally clueless, but I'm extrapolating what's in
> the BU from what would be in if an MN were to send it. If an MN
> sends it, the BU contains the care of address, which is in the
> foreign network. Extrapolating, the MR would have to send a prefix
> that is in the foreign network.

Right, this is what I would call CoP (care-of prefix).  But I'm still
wondering if there's a need to acquire a CoP and renumber all MNN's
when moving.  Keeping the same MR-subnet prefix wherever MR moves can
be done by updating only binding caches of HA's and CN's and not any
routing tables of anyone.  Keeping the same MR-subnet prefix also
leads to "binding cache-free" MNN's.

> The point of the BU in the mobile host case is to tell the HA and CN
> to change its routing to the new address. The point of the BU for a
> MR is presumably to cause a change in the routing tables in subnets
> that are corresponding with host behind the MR, including the home
> network.

Your extrapolation looks right.  With a twist: I would like MR to use
BU like MN/HA/CN use it.  That is update binding caches only and not
routing tables.

> That is, of course, if you want to completely eliminate triange
> routing.

The triangular routing would be eliminated by MR's telling CN's an
association of the form (CoA of MR, MR-subnet prefix).  And not by
telling CN's extrapolated associations like (CoP, Home Prefix).

> This sounds like MIP + a NAT.

As I see it, MR is not NAT because its subnet prefix is
Internet-routable.  By "triangular routing", but still routable.

Also, when CN has learned the MR CoA, it would send a packet to MNN by
putting MR's CoA and MNN's address into a routing header and off it
goes over the net, through MR and to MNN.  With a NAT you can't reach
nodes behind it whatever you try.

NAT uses a sort of translation table containing many-to-one
connections, but MR uses its routing table only.

Alex

---

From: Mattias Pettersson <[email-masked]>
Date: Fri, 17 Aug 2001 13:50:46 +0200

> leads to "binding cache-free" MNN's.

Although a beautiful way, I'm afraid such a renumbering is going to be
something really heavy. Some ISPs are really reluctant to renumbering,
and here we happy Mobile IPv6-people come and suggest mandatory
renumbering every 20 second or so... :)

> telling CN's extrapolated associations like (CoP, Home Prefix).

Exactly. Altering the routing tables of the CN is not enough. You would
need to use MR prefix-routes in every intermediate router between the CN
and MR in order to deliver the packets.

Or do you suggest some tunnelling/routing header mechanism?

/Mattias

---

From: Alexandru Petrescu <[email-masked]>
Date: 20 Aug 2001 10:10:28 +0200

Mattias Pettersson <[email-masked]> writes:
> Although a beautiful way, I'm afraid such a renumbering is going to
> be something really heavy. Some ISPs are really reluctant to
> renumbering, and here we happy Mobile IPv6-people come and suggest
> mandatory renumbering every 20 second or so... :)

Ok, renumbering should not happen very often.  Regarding the ISP, the
renumbering I was thinking of happens in the MMH-subnet only, so
invisible to access network.

This is to say renumbering could be an alternative for small
MMH-subnets.

Alex

---

From: Mattias Pettersson <[email-masked]>
Date: Mon, 20 Aug 2001 10:43:41 +0200

> invisible to access network.

I agree.

BTW, what does the MMH abbreviation mean? I seem to have missed that.

> This is to say renumbering could be an alternative for small

It's not impossible. 

/Mattias

---

From: Alexandru Petrescu <[email-masked]>
Date: 20 Aug 2001 12:46:31 +0200

> BTW, what does the MMH abbreviation mean? I seem to have missed

I think James coined it as Mobile Multihomed Host.  Could have been
MMHH Mobile Multi-Homed Host.

Alex