Subject: Re: [ippm] IPMP : IP Measurement Protocol

From: "Henk Uijterwaal (RIPE-NCC)" <[email-masked]>
Date: Tue, 4 Dec 2001 09:26:06 +0100 (CET)

(Catching up on email after being offline for 2 weeks).

On 16 Nov 2001, stanislav shalunov wrote:

> Matthew Luckie <[email-masked]> writes:
>
> > [Henk writes:]
> >> The most important feature of this protocol is the possibility to
> >> (optionally) include information from intermediate routers, in the
> >> measurement packet.  I think the OWDP we're working on would
> >> benefit from this feature.
> >
> > To give those that haven't read the IPMP specification an idea on
> > how this feature is achieved, we make IPMP echo packets as obvious
> > as we can.
>
> It's important to keep in mind that there's a trade-off between being
> able to get information from intermediate routers and being able to
> test these routers.  In essense, IPMP implies fully co-operating
> routers while OWAMP expects that some routers will be configured to
> cheat and try to make measurement results appear better than they
> would be for ``real'' traffic.  To achieve that goal, OWAMP packets
> are made hard to identify (while IPMP packets are easy to identify by
> design with even a separate IP protocol number).

I agree with this.  What I would like to see is some sort of "switch" that
allows you to use IPMP or OWAMP, use the former if everybody agrees with
the measurement and the latter if there is benefit in hiding the packets.
This is probably best done in the control plane.

Henk

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From: stanislav shalunov <[email-masked]>
Date: 04 Dec 2001 04:00:07 -0500

"Henk Uijterwaal (RIPE-NCC)" <[email-masked]> writes:

> What I would like to see is some sort of "switch" that allows you to
> use IPMP or OWAMP, use the former if everybody agrees with the
> measurement and the latter if there is benefit in hiding the
> packets.  This is probably best done in the control plane.

I guess that's not unreasonable (but we do need to avoid featuritis in
general).  This brings up the next question:

Is IPMP really the right way to do that or would, perhaps, well-known
port numbers have some advantages?

You're not going to run OWAMP-Control in kernel space.  The
co-ordination between kernel and user land on the measurement stations
could quickly become a hassle with OWAMP-Control/IPMP: the amount of
state to hold is potentially large.

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

"The power of accurate observation is commonly called cynicism by
those who have not got it."			-- G. B. Shaw
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From: Matthew Luckie <[email-masked]>
Date: Tue, 4 Dec 2001 02:03:40 -0800 (PST)

> state to hold is potentially large.

There is no issue of co-ordination to consider that I can think of.

The kernel stamps the packets and passes them to userland applications.

I have plans to do an implementation of OWAMP-Control/IPMP as part of my
research in the near future.

Matthew Luckie
[email-masked]