Subject: Re: [nemo] draft-ng-nemo-multihoming-issues-01.txt

From: Chan-Wah Ng <[email-masked]>
Date: 22 Jun 2003 11:00:54 +0800

Hi, Eun Kyoung,

On Sat, 2003-06-21 at 15:47, Paik, Eun Kyoung wrote:
> Hello, Chan-Wha,
> 
> > > > I personally feel that selection of egress interface is an
> > > > implementation issue. But there may be something I missed.
> > > 
> > > Good point. 
> > > We first distinguish the implementation issues from the
> standadization
> > > issues.
> > > If we have to make a consensus ons election of egress interface, 
> > > there may be some different choices, e.g. HA, MRs, and MNN.
> > > 
> > What do other people on the NEMO WG feels about this?
> 
> If we allow multiple BU with multiple CoAs(Care of Prefixes) of
> multiple MRs,
> HA may select the egress interface.
> 

I think you meant this: "given two routes to the same network prefix, HA
has to make the selection which route to use."

It can be based on routing metric, load balancing, or even just a
default route selection.  There shouldn't be any problem in doing that.

> We may also consider the cases that MRs or MNNs select the egress
> interface, however.
> For example, let's imagine the situation as follows.
> There is a big vehicle supports NEMO with multiple MRs.
> As time goes, availability may differes from egress interface to
> egress interface.
> Then, MRs should know and decide which MR's egress interface is
> connected to
> the Internet. So, MRs need to communicate with each other. 
> In this case, MRs select the egress interface as their availability, 
> don't they ?
> 
Right, but I am not too sure if communications between MRs is within the
scope of NEMO. I don't know if you have read the -00 version of the
multihomng draft, but in there, I have described a simple solution to
solve this without requiring special communications.  The solution is
left out of the -01 draft since we want to first identify the problem
before describing solution.

Anyway, here is a brief description:  each MR will actively listen to
the RA in their ingress link(s) to detect the presence of another router
which advertise an egress route to the Internet (lifetime!=0).  When an
MR looses its egress link, it can then set up a temporary tunnel with
its HA that passes through the other MR.  This way, we don't need any
special communications between MRs, and the MR can decide which route to
use specifically.

Another way to do it is for the MR to simply response with an ICMP
re-direct message when it looses its egress link.

The first way, the lost of egress link is transparent to MNNs.  The
second way, the MR inform MNNs that it has lost a route, and force MNNs
to re-direct their packets to other MRs.

/rgds
/cwng

---

From: Chan-Wah Ng <[email-masked]>
Date: 22 Jun 2003 11:00:54 +0800

Hi, Eun Kyoung,

/rgds
/cwng