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Subject: Re: How to find a sick router with 2.6.17+ and tcp_window_scaling enabled
Date: Tue, 15 Aug 2006 14:07:20 -0400
Message-ID: <Pine.LNX.4.61.0608151404220.29941@chaos.analogic.com>
In-Reply-To: <44E208AC.2050906@everytruckjob.com>
Thread-Topic: How to find a sick router with 2.6.17+ and tcp_window_scaling enabled
thread-index: AcbAlabFllpjEcAPSN6E+Jnk33OmGQ==
References: <44E1F0CD.7000003@everytruckjob.com> <1155661308.24077.297.camel@localhost.localdomain> <20060815173046.GA2034@linuxace.com> <44E208AC.2050906@everytruckjob.com>
From: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
To: "Mark Reidenbach" <m.reidenbach@everytruckjob.com>
Cc: "Phil Oester" <kernel@linuxace.com>, <linux-kernel@vger.kernel.org>
Reply-To: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3019
Lines: 69


On Tue, 15 Aug 2006, Mark Reidenbach wrote:

> Phil Oester wrote:
>> On Tue, Aug 15, 2006 at 06:01:47PM +0100, Alan Cox wrote:
>>
>>> Ar Maw, 2006-08-15 am 11:05 -0500, ysgrifennodd Mark Reidenbach:
>>>
>>>> Does anyone have a way to find the broken router if you are not running
>>>> the networks involved?
>>>>
>>> You are almost certainly looking for a broken/crap NAT box, firewall or
>>> similar product. Routers that are just being routers don't touch the TCP
>>> layer so even if they are broken/crap/ancient they won't do any harm to
>>> it.
>>>
>>> The usual offenders are cheap NAT boxes and badly designed load
>>> balancers. They may not even show up in a trace but you should expect
>>> them to be at one end or the other, unless your ISP is providing you
>>> with NATted addresses or some kind of managed security service.
>>>
>>
>> Certain versions of BSD ipfilter are also broken.  Try some of Apple's
>> websites for examples.
>>
>> Is the destination box BSD or behind a BSD firewall?
>>
>> Phil
>>
> I'm not sure what OS the T1 provider's box is running.  I experience the
> same problems trying to access kernel.org or one of my servers hosted at
> Verio in Sterling, VA.
>
> Alan Cox says it's most likely a broken NAT box or firewall.  I'm not
> aware of any firewalls in between my office and my servers in Sterling
> other than the Cisco 1811 here in the office, and it is performing NAT
> and firewall services for our office.  I'm going to try a few cheapo
> home routers and see if the problem remains.  I would think the Cisco
> router would be better off than a home Linksys or Xincom one, but I
> figure it's at least worth a try.
>
> Thanks for your help.
>
> Mark Reidenbach
> EveryTruckJob.com
> M.Reidenbach@EveryTruckJob.com
> Phone: (205)722-9112

Some older Ciscos need to be upgraded to handle the ECN bit. If
your router is a couple years old and has not been upgraded, this
might be the problem. A few years ago, vger started running a
new kernel that used ECN. The result was chaos for a few weeks.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.62 BogoMips).
New book: http://www.AbominableFirebug.com/
_


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