Linux Router: TCP slow, UDP fast

Nickola Kolev nikky at
Sat Feb 14 14:18:54 UTC 2009

Hello, Chris,

So, as it seems you have problem with TCP, and not UDP, maybe this is
something with regard to TCP segmentation offloading.

It could be a total shot in the dark, but can you see what
ethtool -k <devname> says?

Then you can have a look at 'man ethtool' and turn on/off the appropriate

On Sat, 14 Feb 2009 13:48:53 +0000
Chris <chris at> wrote:

> Thanks loads for the quick replies. I'll try and respond individually.
> Lee > I recently disabled tcp_window_scaling and it didn't solve the
> problem. I don't know enough about it. Should I enable it again ? Settings
> differing from defaults are copied in my first post.
> Mike > Strangely I'm not seeing any errors on either the ingress or egress
> NICs:
>           RX packets:3371200609 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:3412500706 errors:0 dropped:0 overruns:0 carrier:0
> The only errors I see anywhere are similar on both NICs. Both connect to the
> same model of switch with the same default config:
>      rx_long_byte_count: 1396158525465
>      rx_csum_offload_good: 3341342496
>      rx_csum_offload_errors: 89459
> and it may be worth noting that flow control is on. Are these a reasonable
> level of pause frames to be seeing ? They seem to be higher on non-routing
> boxes.
> Total bytes (TX)2466202288Unicast packets (TX)3436389971Multicast packets
> (TX)213310Broadcast packets (TX)4952902Single Collision Frames (TX)0Late
> Collisions (TX)0Excessive Collisions (TX)0Transmitted Pause Frames (TX)27806
> Florian > They're running without obvious errors. Auto Neg has taken 1Gbps,
> Full. Can Auto Neg cause these symptoms do you think ?
> Thanks again,
> Chris

Best regards,

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