Subject: [nemo] Multiple Egress vs multihoming

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Wed, 23 Apr 2003 09:38:50 +0100

In the v 00 of the requirements, Thierry had the multihoming included. 
This was discussed at the WG and you'll find the summary at
http://www.nal.motlabs.com/nemo/ietf56/chat-ietf56.txt

Since the requirement draft is the base for the design, I suggest we
finalize that one first, what do you think?

I understand that r16 is gone, so is r14.4. As of multihoming, I
understand that we would give names to specific situation, multihoming
being a catch all.

Now, if you look at this requirement:

      R13.1: The solution MUST support mobile networks with multiple
MRs,

I understand it as one mobile prefix owned by several MRs, considering
the problems Erik raised otherwise.

Say we have 2 MRs, MR1 and MR2. If there's no coordination between the
2, they may register to 2 different HAs.
One of them may be at home and not the other.

This impacts the choice of routing model between the HA and the MR. We
have 3 approaches:

- static: a static route in the HA(s) to the mobile profix via the MR
home address. Implicit in all drafts.
->If we use static, then the 2 MRs have to have the same home address or
to be both available at all time, because the HA will distribute the
packets over the available static routes. If they have the same Home
address, then the model is close to one MR, multiple careof (multiple
interfaces), as long as the 2 MRs register to the same Home Agent. In
case of DHAAD, this requires coordination between the MRs. 

- dynamic: MR tells HA about the mobile prefix. Present in Ryuji's and
TJ's draft.
-> Dynamic should work. But if one MR is at home and not the other, the
redistribution model must be studied. Note that there's no requirement
for home coming in version 00 of the draft. But that we were close to
reach a consensus that this model is not part of basic Nemo. Do we want
to open Pendora's box?

- delegation: HA tells MR about the mobile prefix. MR installs the
prefix. Present in Pekka's draft, and should be working using DHCP-PD on
MRHA as well.
-> Delegation must be extended to let the DHCP server know that those 2
MRs are paired. Again, this is not supposed to be addressed in basic
Nemo.

All this to say that in my humble view, dynamic will be the enabler for
R13.1. As a consequence, I believe that this requirement should be
delayed and not part of basic Nemo. What do you think?

Pascal

---

From: Chan-Wah Ng <[email-masked]>
Date: 23 Apr 2003 18:37:16 +0800

Hello Pascal,

> delayed and not part of basic Nemo. What do you think?

I beg to differ.  Requirement 13.1 does not equate to "Multiple MRs with
different HAs advertising same prefix".  Why in the first place would
two MR choose to advertise the same network prefix if they does not
belong to the same administration domain?

For static:
Why would we require both MR to be on at the same time?  If one MR is
down, its corresponding HA will not receive any BU from that MR, and
thus cannot establish a route to that MR.  Hence it will respond to any
packet that is destined to the mobile prefix with a ICMP destination
unreachable or ICMP redirect messgae.  Just as in the case of w
non-mobile, multiple router scenario.

In addition, I don't understand why DHAAD would require co-ordination of
both MRs, unless you are saying the two MR must discover the same HA. 
Question then is why?

-- 
Chan-Wah Ng <[email-masked]>
Panasonic Singapore Laboratories