Linux Router: TCP slow, UDP fast

Mathias Wolkert mathias.wolkert at gmail.com
Sun Feb 15 04:10:44 CST 2009


I would turn off ethernet flow control. Maybe you already have.

It can be really mean on tcp's own flow control if the switch has an  
issue of some kind (load).

/Tias

15 feb 2009 kl. 10.24 skrev Chris <chris at ghostbusters.co.uk>:

> Thanks, Karl, Allen and Nickola.
> I failed-over to another router last night and briefly had full  
> expected
> throughput but this morning despite dropping providers and moving  
> between
> routers again for trial and error I still see _outbound_ TCP at  
> about the
> same 300 - 600kbps per session.
>
> I eliminated conntract modules firstly, then iptables as a whole. I've
> eliminated TSO and checksumming (which caused very sticky  
> connections) on
> the e1000 NIC.
>
> The failover router has a slightly older kernel and was working before
> Christmas so it's not most likely not kernel versions. I've also tried
> removing FIB_TRIE as a stab in the dark with no success. And the  
> failover
> router connects using FE not GE so I've eliminated NICs and connection
> speeds to a front-facing switch.
>
> The only constant is the front-facing switch (it's negotiating  
> perfectly at
> FD though) so all I can think of is removing that from the equation.
>
> It's definitely only _outbound_ TCP getting buffered though ! I've  
> pushed
> 92Mbps on a FE link with UDP and uploaded at 16Mbps on a 16Mbps link.
>
> Any last ideas appreciated before causing headaches removing  
> switches would
> be appreciated.
>
> Thanks,
>
> Chris





More information about the NANOG mailing list