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jgrotepass
Titel: Weird Connectivity issues with 2.6.17 Kernel versions  BeitragVerfasst am: 06.07.2006, 19:47 Uhr



Anmeldung: 21. Jun 2006
Beiträge: 4

I already posted it in the German network folder, but it might be worth to put this here too.

In Kernel version 2.6.17 is a redesign for allocating rmem and wmem parameters of the IP stack. This result in probable connection issues.
Depending on other boxes on the way like Firewalls, Routers or even the Server connection might fail or data retrieval will not succeed.

A possible workaround is to set the window-scaling option to "disable" via the /etc/sysctl.conf
Just enter
net.ipv4.tcp_window_scaling=0

Another way is to adjust the "max" Value for both the
net.ipv4.tcp_rmem and
net.ipv4.tcp_wmem

The original discussion was found here
http://kerneltrap.org/node/6723

Keep on the good work

Regards,
Jochen
 
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Crust
Titel: RE: Weird Connectivity issues with 2.6.17 Kernel versions  BeitragVerfasst am: 06.07.2006, 19:54 Uhr



Anmeldung: 20. Okt 2005
Beiträge: 278

It may be because I use the 2.6.17.3-slh-up-1 version, but everything seems fine with me. www.everymac.com looks fine to me. (I could be missing something)

-Crust
 
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piper
Titel: RE: Weird Connectivity issues with 2.6.17 Kernel versions  BeitragVerfasst am: 06.07.2006, 20:00 Uhr
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Anmeldung: 03. Mai 2005
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hmm, I can't access this ......... http://www.everymac.com/

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slh
Titel: RE: Weird Connectivity issues with 2.6.17 Kernel versions  BeitragVerfasst am: 06.07.2006, 20:15 Uhr



Anmeldung: 16. Aug 2004
Beiträge: 1905

It will only fail if one of the routers higher up in the chain is broken and doesn't support scaling properly, this is something to fix - not in the linux kernel which conforms to accepted standards, but in affected systems.
 
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jgrotepass
Titel: Re: RE: Weird Connectivity issues with 2.6.17 Kernel version  BeitragVerfasst am: 06.07.2006, 20:19 Uhr



Anmeldung: 21. Jun 2006
Beiträge: 4

Crust hat folgendes geschrieben::
It may be because I use the 2.6.17.3-slh-up-1 version, but everything seems fine with me. www.everymac.com looks fine to me. (I could be missing something)

-Crust

I guess that they switched the server to window-scaling disabled.

We made the experience by accessing a 2.6.17er box via a vpn. It worked perfect with 2.6.14 and 2.6.16. Switching to 2.6.17 we were unable to get the ssh connection.
Analyzing the tcpdump, we found that the window-size was lowered extremely when the Init-Key-Exchange took place. We did not receive the Key-Exchange from the ssh-server.
Playing around we saw some differences in the tcp-parms.
The rest was googling until I found the mentioned article.

We have a similar network structure than the one that failed and did not had any issues.
So, it is a weird issue that gives no clear indication why something doesn't work. For this reason I thought I should post it here to give a hint if something fails.

Jochen
 
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piper
Titel: Re: RE: Weird Connectivity issues with 2.6.17 Kernel version  BeitragVerfasst am: 06.07.2006, 20:35 Uhr
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slh hat folgendes geschrieben::
It will only fail if one of the routers higher up in the chain is broken and doesn't support scaling properly, this is something to fix - not in the linux kernel which conforms to accepted standards, but in affected systems.


So is my router broke ? Winken

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slh
Titel: Re: RE: Weird Connectivity issues with 2.6.17 Kernel version  BeitragVerfasst am: 06.07.2006, 23:17 Uhr



Anmeldung: 16. Aug 2004
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piper hat folgendes geschrieben::
So is my router broke ? ;)

Maybe your router, maybe on of your ISP's routers, maybe a router just in front of the webserver you're about to visit, maybe some router you're coincidently passing - time to investigate.
 
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schnorrer
Titel: RE: Re: RE: Weird Connectivity issues with 2.6.17 Kernel ver  BeitragVerfasst am: 07.07.2006, 00:21 Uhr



Anmeldung: 09. Jan 2006
Beiträge: 1721

No piper not by default. Your router NIC's has a fixed RX/TX-Buffer size between 256 and 32K for each Dir and Port.

What they discuss is the buffer in the PC corresponding to NEW Cpu-handled NIC's. This means the cpu does the convert parallel to serial and the linking to the PHY for Voltage converting. Older NIC's may not have this kind of problem. Even so older Chipsets which controlls the memory.
 
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piper
Titel: RE: Re: RE: Weird Connectivity issues with 2.6.17 Kernel ver  BeitragVerfasst am: 07.07.2006, 01:57 Uhr
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Thanks slh, schnorrer for explaining it to me Smilie

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xweber
Titel:   BeitragVerfasst am: 07.07.2006, 07:39 Uhr



Anmeldung: 20. Okt 2004
Beiträge: 64
Wohnort: Kaiserslautern
same to me, unreachable

then with
Code:
sysctl -w net.ipv4.tcp_window_scaling=0


its working.

so i will put
Code:
net.ipv4.tcp_window_scaling=0

in the sysctl.conf

Alex
 
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Swynndla
Titel:   BeitragVerfasst am: 07.07.2006, 08:51 Uhr



Anmeldung: 05. Dez 2005
Beiträge: 414
Wohnort: Auckland, New Zealand
I can't get to http://www.everymac.com/ from either:
2.6.17-kanotix-1
or:
2.6.17.3-slh-up-1

Putting:
net.ipv4.tcp_window_scaling=0
in:
/etc/sysctl.conf
works after a reboot
... or this works without having to reboot (as I discovered on my other pc):
/sbin/sysctl -p /etc/sysctl.conf

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piper
Titel:   BeitragVerfasst am: 07.07.2006, 17:28 Uhr
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All good here now too Winken

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jgrotepass
Titel:   BeitragVerfasst am: 07.07.2006, 19:46 Uhr



Anmeldung: 21. Jun 2006
Beiträge: 4

Just as a quick reminder:
Setting window-scaling to 0 means that there might be some performance degradations. Especially with High-Speed Links this can delay the response.
I am currently looking for a setting of
net.ipv4.tcp_rmem
and
net.ipv4.tcp_wmem

that will work without any trouble.
There is a discussion that the old values (until Kernel 2.6.16) might result in some issues - at least they worked...

Also, the amount of Memory is related to this issue, because both vaules for rmem and wmem are calculated from there.

So setting window_scaling=0 is just a "quick-and-dirty" Workaround

It really seems that there are specific boxes involved in this issue (in the middle).

Cheers,
Jochen
 
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schnorrer
Titel:   BeitragVerfasst am: 07.07.2006, 23:49 Uhr



Anmeldung: 09. Jan 2006
Beiträge: 1721

@jgrotepass, this missleading widow_scaling can have more than one reason.

R1: memory mapping between NIC's-Ram and DMA. let it lead to bufferoverfflow when Buffersize is to large for dma.
R2: Paket to large to fit in Buffer either in NIC's-Ram or w(w)mem. Let it lead to a NAK-cycle and a resend-paket.
R3: window_size and position has changed within the addresss-space where the buffers should found
R4:New Soft-NIC is used and w/rmen window is within the cache. Cachemiss while the next paket should written or read by the CPU.
R5: more exceptions can occure at the same time

Best way to get rid use window_scaling=0
 
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