[c-nsp] Centos upload speed slower on 1000m than 100m over WAN links

[Lee]

On 6/28/10, Joe Loiacono <jloiacon at csc.com> wrote:
> OK I'm jumping in on this thread late as I just got back from some
> vacation, don't know if this particluar observation has been discussed,
> but ...
>
> We've seen this problem a lot when moving up to new local connection
> speeds. The problem for us has been that unless the entire path can
> support the new speed (e.g., 1G) switches down the path that connect to
> slower speeds (e.g. 100M) will overflow and put your data transfer into
> TCP slow-start recovery. As soon as the sending NIC is 'downgraded' (e.g.,
> back to 100 M) the overflows disappear, slow-start is avoided, and
> performance improves. Bitterly ironic.

Have you checked to see if selective acks are enabled on both sides of
the connection[s]?

Lee


>
> Joe
>
>
>
> From:
> Paul <paul at gtcomm.net>
> To:
> cisco-nsp at puck.nether.net
> Date:
> 06/27/2010 03:08 AM
> Subject:
> [c-nsp] Centos upload speed slower on 1000m than 100m over WAN links
>
>
>
> I'm not even sure this is the right forum but since we use mainly Cisco
> equipment I'll give this a shot. :)
> I have tried several centos based servers and compiled various kernels
> and the results have been extremely weird.
> 90% of the cases the remote hosts can download from a server at
> 1-5megabytes per second, and most of these are over
> the internet ranging from 30-200ms away.  Local (1ms or less) is super
> fast 100MB/s for example.
> Ok that sounds normal since it's going over the internet, etc.  But
> here's the )(!@*! part..
> If I set the port speed to 100 megabits full duplex on the switch and
> server , the clients that get 1-5MB/s now get 11MB/s which is
> approximately the limit of the 100mbit port.
> Totally stumped here, tried different nics, servers, even 4 different
> switches.  Is a very interesting problem and I'm probing to see
> if anyone else has encountered it.
> So far the only OS i have tried is centos, but different versions and
> kernels and hardware.
> All the switches/routers are Cisco based, but I seriously doubt that has
> anything to do with this. :P
>
> --
> GloboTech Communications
> Phone: 1-514-907-0050 x 215
> Toll Free: 1-(888)-GTCOMM1
> Fax: 1-(514)-907-0750
> paul at gtcomm.net
> http://www.gtcomm.net
>
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