Using gigabit NIC and switch with 100Mbps clients doesn't work

[Gavin McCullagh]

Hi,

On Wed, 03 Jan 2007, Scott Ledyard wrote:

> It's suggested that the server connect using a gigabit NIC to a gigabit
> switch port. I've installed Edubuntu 6.10 accordingly and find that clients
> cannot connect successfully. The NIC works fine when used with a 100Mbps
> switch. The gigabit switch (D-Link DGS-2208) seems to work well in other
> situations. The client is an old IBM PC 300GL using a Intel 10/100 Intel
> NIC.
> When the thin client boots (using Ethreboot so the boot dialog displays) is
> can see that the server has assigned the thinclient the IP of
> 192.168.0.250then it displays:
> Running /scripts/init-btom... Done.
> Then it waits for about 60 seconds and displays [ 103.939343] nfs: server
> 192.168.0.254 not responding, still trying.
> This repeats every 15 seconds or so. If I replug both the server and
> thinclient into a 100Mbps switch EVEN DURING this time, all works well.
> Has anybody seen this behavior before? Any suggestions?

The behaviour suggests your client cannot get to the nfs server while
you're on the 1Gb port but can when you're on the 100Mb port.  That's quite
strange.  It's certainly not fundamental to gigabit use -- we have a server
on 1Gb and it works fine.

It sort of looks like there's something wrong with the gigabit link but
it's strange that you say it works in other situations.  Perhaps you're
getting packet loss but this is only obvious in certain applications whose
error checking is not so good (ie UDP ones such as NFS).

A few guesses would include:

 - a faulty or below spec cable (for GBit you should need Cat5E/Cat6)
 - software errors at gigabit speeds
 - a slightly bad gigabit connection on the switch
 - some ACL rule blocking nfs traffic on the gigabit port of that switch
   (if the switch is even capable of that)

You could try checking:

 - output of /sbin/ifconfig for errors
 - /var/log/syslog and /var/log/messages for errors
 - try bringing up a linux machine (not as a thin client) and see can you
   consistently mount the nfs share by hand on 100Mb and 1Gb.
 - ping the server for a while on each port and see is there any difference
   in losses (both should presumably be zero).

Let us know how you get on,

Gavin