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

From: James Kempf <[email-masked]>
Date: Thu, 16 Aug 2001 10:36:11 -0700 (PDT)

>> Not to mention BGP. Should a BGP autonomous system be advertising
>> prefixes for "care-of" subnets, i.e. subnets that get their prefixes
>> doled out to mobile routers when they arrive, even though there may
>> be no mobile network there yet?
>
>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? 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. I'm
not a BGP expert, so maybe there is some clever way around this.

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. So other than for handling routing
updates and sending routing advertisements, it is not clear what
a "home address" means for a router. Am I missing something?

		jak

---

From: Alexandru Petrescu <[email-masked]>
Date: 16 Aug 2001 20:33:29 +0200

James Kempf <[email-masked]> writes:
> 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?

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.

Alex

---

From: Mattias Pettersson <[email-masked]>
Date: Fri, 17 Aug 2001 13:35:20 +0200

> not a BGP expert, so maybe there is some clever way around this.

I hope that what is happening at the edges of the foreign ISP won't be
reflected to BGP.

The CoP (if we now should have one) could be allocated by the MR from
the AR at the foreign ISP. The method used could be the prefix
delegation draft.

If the MR is there, the CoP is being used and should of course be a
routeable prefix. MR and AR would announce it upstream (but probably not
with BGP, but RIP or OSPF).

If MR is not there (or no other MR), the CoP is not being used and the
AR keeps it in its prefix pool. Now, AR still announces it upstream.

In both cases, aggregation is used outside the ISP, so that BGP doesn't
have to know about the CoP - it is rather a subset of the aggregated
address space of the ISP.

> a "home address" means for a router. Am I missing something?

But a MR is still a node as well. It could initiate and terminate
traffic just like any other node, if someone it currently using it as a
client/server or whatever. For this, it needs a home address.

/Mattias