Subject: [IMRG] Is there any work on IP option support in Internet?

From: "Zheng Zhang (W&N)" <[email-masked]>
Date: Tue, 9 Sep 2003 10:24:48 +0800

Hello all,

Is there any work that characterizes the routers' support in Internet for various IP options, e.g. timestamp, record route, source routing, etc, using a measurement-based study? How many routers support these IP options in current Internet? To the best of my knowledge, the only related work is "Ramesh Govindan, Hongsuda Tangmunarunkit, Heuristics for Internet Map Discovery, IEEE INFOCOM 2000". In addition to some heuristics for Internet map discovery, the authors studied the support for source routing IP option in Internet. They found that only a small fraction (about 8%) of routers support source routing.

And it is known that some routers would drop the packets with IP options they don't understand. Is there any work that studies how prevalence those routers are in current Internet?

A pointer to more information will be much appreciated. Thank you, all.

Best wishes,

Zheng Zhang, W&N Group, Microsoft Research Asia

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From: Mark Santcroos <[email-masked]>
Date: Tue, 9 Sep 2003 23:59:51 +0200

Hi Zheng,

I don't have numbers from studies, but I did some work with IP options,
read on ...

On Tue, Sep 09, 2003 at 10:24:48AM +0800, Zheng Zhang (W&N) wrote:
>    Is there any work that characterizes the routers' support in Internet
>    for various IP options, e.g. timestamp, record route, source routing,
>    etc, using a measurement-based study? 

Basically, our intention was to use the timestamp field for timestamping
purposes (surprise surprise). However, the spec/RFC (don't have the number
handy) defines only a time in ms, which is not that great.
We changed some machines we had control of to encode the time in us/ns.
While that of course worked, it was not very practical and useful.

>    And it is known that some routers would drop the packets with IP
>    options they don't understand. 

The routers I tested, didn't drop them, but clearly put them on a
different processing queue. We saw relatively huge differences in the
processing time of packets with IP options and packets without.

We concluded that IP options were not useful for the purpose we wanted to
use them: accurate delay measurements.

Most of the above facts don't play a role in record-route, source-route,
etc. But as you already refer to, study and practice has turned out that
in the "real Internet", IP options are not widely supported. (High volume
routers simply don't have the processing power to do that)

Mark

-- 
Mark Santcroos                    RIPE Network Coordination Centre
http://www.ripe.net/home/mark/    New Projects Group/TTM

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