[X-Unix] [OT] TCP ACK...

[Simon Forster]

On 2 Feb 2006, at 21:58, Stroller wrote:

>> A bit more detail for those interested: We're accepting (on  
>> machine B) an HTTP file upload from a telco (sent by machine A) -  
>> unfortunately, frequently the uploaded data is truncated  
>> (particularly large files during busy times). I've looked at  
>> output from tcpdump, and  can quite clearly see the data coming in  
>> from machine A and ACKs going out fro machine B after every couple  
>> of datagrams (terminology?). On the interrupted feeds, you'll see  
>> an ACK go out... and then nothing. After 5 minutes, our server  
>> sends a finish every one minute, after which a reset will be  
>> returned (sometimes after a few finishes have been sent).
>
> I would take the stance that this is pretty damning evidence that  
> the other party's machine isn't doing it's job, although to be  
> honest I'd feel happier if I were seeing it by packet-sniffing on a  
> second machine (I bridged two network interfaces on a second  
> machine and ran ethereal, I think, maybe snort, when I wanted to do  
> this). There's surely no way to prove (with the equipment available  
> to you) that the ACK packets are leaving your network past the ADSL  
> router, but a reasonable log of what you're seeing should be  
> sufficient to pass the onus onto the other party to prove that  
> their machine isn't misbehaving.

Stroller

How goes it?

I've had the client's network guys check the firewall and they're  
seeing the TCP acknowledgement packet from us going out. At the  
moment we're playing a game of "who blinks first" with the telco  
guys, and I think they've blinked by escalating this on to the  
application development guys. Now I want to know why. I think it's  
'cause their server should initiate the next TCP event - because they  
haven't received an acknowledgement from our server. However, I'd  
like to know for sure. It's called lining up your ducks just in case ;-)

And beer sounds very good. Sunday or Monday for a swift pint,  
Wednesday for a more leisurely sup of ale.

ATB

Simon Forster
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