[Iccrg] RE: Testing ECN support for UDP flows

[Ingemar Johansson S]

Hi

Tried with an MS-Windows version of tracert (ftrace), it was supposed to be able to set the ToS field. However it seems like when I run wireshark that the modified ToS field does not stick, it could be some Windows specific feature that simply clears the ToS field. I will try some traceroute tests on our Linux boxes next week when I really start working. It could be that this will do.

I also tried http://www.microsoft.com/windows/using/tools/igd/default.mspx as it claimed that my homelaptop is indeed ECN capable. The test seems however to be a bit limited and perhaps a bit faulty. The SYN packet sets ECE and CWR according to RFC3168, the ECE flag is however not set in the SYN-ACK packet, still the ECN test is marked as passe!. Also the ECN bits are never set in any subsequent data traffic which means that AFAIK nothing is really tested.

I have not looked at PlanetLab earlier, will have a look at it, thanks for the tip.

Regards
/Ingemar

> -----Original Message-----
> From: p.ohanlon at gmail.com [mailto:p.ohanlon at gmail.com] On 
> Behalf Of Piers O'Hanlon
> Sent: den 20 augusti 2009 18:38
> To: Ingemar Johansson S
> Cc: iccrg; tsv-area; carlberg; Colin Perkins; Magnus Westerlund
> Subject: Re: Testing ECN support for UDP flows
> 
> Hi Ingmar,
> 
> I found that one could do some quite useful tests using (on 
> Linux) traceroute -t <tos> hostname. Linux machines seem to 
> reflect the TOS byte contents even in ICMP error responses 
> and ICMP echos. Though DSCP bits are usually reset the the 
> ECN bits are more resilient... Since traceroute uses UDP as 
> default it's quite a neat test. And it seems that ICMP time 
> exceeded responses are more likely to get thru router filters 
> than plain ICMP responses - and the can carry ECN markings.
> Though it seems that that there maybe some bugs in certain 
> routers as I've seen the TOS byte reversed in some replies?!
> 
> As ken mentioned - I was thinking that wide area testing 
> could be most easily done using PlanetLab - though as far as 
> I'm aware it doesn't tunnel packets - though packet timings 
> can get skewed by the vserver implementation. Also the 
> network sharing system in use on Planetlab can make things 
> tricky if someone else on that machine using the same ports.
> 
> Additionally it may be worth checking with the methodology 
> used by Floyd et al when they did their [tcp] tbit testing:
> http://www.icir.org/tbit/ecn-tbit.html
> 
> Piers.
> 
> 2009/8/20 Ingemar Johansson S <ingemar.s.johansson at ericsson.com>:
> > Hi
> >
> > Sorry for the cross-post, I would believe that it is best 
> to reply to tsv-area only.
> >
> > I have previously asked people regarding the support of ECN 
> especially 
> > for UDP flows.. There seems to be a lot of uncertanities 
> around this and in general it is difficult to get any clear 
> view (if there is any ?) So... how do I best test this on a 
> larger scale ?
> >
> > 1) UDP port 7: The idea is to ping other host with UDP 
> packets on port 7, some of the packets are ECT(0)/(1) marked, 
> some are not. If I get things right, port 7 is not genarally 
> enabled these days, are there any host around that are known 
> to leave port 7 open.
> >
> > 2) Modified STUN client: The idea is to do STUN requests to 
> a number of STUN servers. Some of the STUN requests are ECT.
> >
> > 3) Setup a mesh of volountary hosts that installs a 
> software that agrees to communicate via a specific port, the 
> hack would need to implement some means to communicate NAT'ed 
> addresses etc. This would require some logistic effort to 
> gather up volounteers for the test-fest.
> >
> > Ideally the test should be able to tell if possible ECN 
> issues are located close to the user (e.g firewalls, WLAN 
> routers etc) or in the core-networks. Also I believe that 
> running UDP would be beneficial even though I know some 
> people have already tried with ICMP.
> >
> > Which would be the best alternative in order to do such a 
> test ?, comments/suggestions are welcome.
> >
> > Regards
> > Ingemar
> >
> > *******************************************
> > Ingemar Johansson
> > Senior Research Engineer, IETF "nethead"
> > EAB/TVK - Multimedia Technologies
> > Ericsson Research Ericsson AB
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> >
>