Re: How to find a sick router with 2.6.17+ and tcp_window_scaling enabled

From: linux-os (Dick Johnson)
Date: Tue Aug 15 2006 - 14:05:25 EST

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 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
> M.Reidenbach@xxxxxxxxxxxxxxxxx
> 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.

Dick Johnson
Penguin : Linux version on an i686 machine (5592.62 BogoMips).
New book:

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