[Ukfreebsd] Copper port link strangeness

andy thomas andy at time-domain.co.uk
Thu Aug 15 23:09:20 BST 2013

On Wed, 14 Aug 2013, Jon Schneider wrote:

> Sorry for the completely off-topic mail but I know some of you deal with
> infrastructure.
> Has anybody seen any issues with copper ports on a large manufacturer's
> router model 28xx or 3945 unexpectedly not linking with _certain_ other
> pieces of kit ?

I have had problems in the past with Intel Pro100 NICs refusing to 
auto-negotiate an error-free full duplex link with Cisco 1910 10 Mbit/s 
switches - they'd negotiate a half-duplex connection with a huge number of 
collisions & TCP re-transmits. Attempts to force either end to negotiate a 
fixed 10 Mbit/s FD connection would result in no link at all. The 
workaround I eventually adopted was to put a cheap 100 Mbit/s D-Link 
switch "in series" between the Cisco and the servers with Intel Pro100 
NICs - both were happy to auto-neg with the D-Link switch.

> Or links that come up and go down at random but without any errors
> (including but not limited to FCS, Jabber, RxErrors...) when up ? Cable
> problems ruled out.

Occasionally, some servers we have with Broadcom giga-bit NICs connected 
to 3Com switches will suddenly drop from 1000 Mbit/s FD down to 10 Mbit/s 
HD for no apparent reason. Restarting networking services on the servers 
sometimes resolves this but more often I need to power-cycle the switch. 
No idea why this happebs but it does!

> Sorry this is a bit vague but that's how strange some problems we've seen
> recently are.

Yeah, I've seen weird things happen...


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