Linux Router: TCP slow, UDP fast

Lee ler762 at
Sat Feb 14 14:57:13 UTC 2009

On 2/14/09, 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.

I don't know if the tcp window size makes any difference when the box
is acting as a router.  But when UDP works as expected & each
additional TCP connection gets 300-600kbps the first thing I'd look at
is the window size.  If it was a duplex mismatch additional TCP
connections would make things worse instead of each getting 3-600Kb

> The only other change to the box is that over Christmas IPtables
> (ip_conntrack and its associated modules mainly) was loaded into the kernel

If all else fails, backing out recent changes usually works :)


More information about the NANOG mailing list