Subject: RE: [nemo] Re: BU adds routes (was: Draft NEMO Agenda)

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Mon, 18 Nov 2002 22:11:59 -0000

Hi Erik:

> Depending on the address allocation inside the site these 
> routes might be aggregatable at the HA. For instance, if a HA 
> serves multiple MRs the Nemos attached to those MRs might get 
> addresses allocated so that the HA can inject a single route 
> into the IGP for all of them. Then the HA would only install 
> its local routes to the individual Nemos when the tunnels are 
> up. This would reduce both the size of the routing tables and 
> the rate of change to them, but it assumes that a given MR 
> always connects to the same MR. (Well, a longer prefix can be 
> injected should it connect somewhere else.)
> 

Hopefully this aggragtion exists soon as the number of MR grows. The
result is that all home agents advertise the aggregation at all times.
So any of them may get a packet to an individual Mnet at all time. And
need the Mnet->MR route present, either static/permanent or obtained
from the HA that got the registration. I do not see the value/cost ratio
of making that dynamic through a routing protocol since ND has to be
performed anyway. This is the point I tried to make in my earlier mail
when I said that "Another belief is that ND should be the one doing link
level resolution, not routing protocols". 

> There might be cases where one wants to multihome a MR (hence 
> a Nemo) at two different HAs inside the routing domain. Thus 
> the MR would have two different home addresses (and home 
> links). The MR establishes a tunnel with both HAs and both 
> HAs (when the tunnel is
> up) injects a route into the IGP. Thus uses the IGP to get 
> redundancy against HA and home link failures, but it assumes 
> that there is some basic liveness checks on the tunnels to 
> detect when a tunnel stops working.

In many cases -that would be a measure of our success-, the mobile nets
will be too numerous to be advertised individually at the normal, global
routing plane . Hopefully, the model will be of targetted, localized
routing overlay around the Correspondent (thus the concept of
correspondent router that I mentioned in my RO draft).

MIP HA redundancy will possibly be the primary mean for high
availability of MN, but there's no rule to impose. If the MNet can be
reached via 2 different HA clusters at any point of time, then
redistributing the aggregation from both HA sets still works.

If a Correspondent can not reach a HA cluster at all, then the
aggregated route to all MNets goes away with it - that one has never
been static- and the Correspondent has no choice but use the alternate
cluster. Seems to me there's no need for individual MNet routes, but for
RO. 
Is that correct?

Pascal

---

From: Erik Nordmark <[email-masked]>
Date: Tue, 19 Nov 2002 03:49:28 +0100 (CET)

> correspondent router that I mentioned in my RO draft).

My use of "inside the routing domain" was trying to say that
clearly you want these routes to aggregate in the IGP for the routing domain
and not appear as separate routes in the DFZ.

> redistributing the aggregation from both HA sets still works.

I don't understand. Was is a "HA cluster"? Are they on the same link
or in different parts of the routing domain?

   Erik