[CentOS] [OT] Network switches

Tue Mar 24 20:49:49 UTC 2009
Les Mikesell <lesmikesell at gmail.com>

Rainer Duffner wrote:
>>   i am often not very
>> impressed by network performance and need standardized benchmarks to
>> figure out if there may be an issue at the NIC driver, switch or on up
>> to a virus shield.   It was either a ~2004 Dell Power magazine or
>> ~2004 Network World article that mentioned that 3Com NICs didn't
>> perform well with Cisco switches and vice versa.
> Hm. I think I saw something like that (I was at a site that used
> Catalyst 6500-switches to connect desktops - in 2001).
> Autosensing was useless...

They've had that fixed for most of this century...

>>   They also wrote
>> about other vendors and i don't remember any of them performing
>> extremely well across vendor.   Now that NICs are a commodity, the
>> problem could be worse.

> Here, autosensing sometimes doesn't work. Then, you've got to set it
> fixed on both the client and the switch-port.

Usually the problem is that due to earlier Cisco autosensing issues you 
have set the switch configuration to not negotiate and replaced the 
connected device with one that does.  With current equipmement and 
software auto negotiation almost always works, but if one end has been 
locked, the other has to assume half-duplex which is always wrong.

If you still have very old equipment you might still have to lock a port 
or two.  Strangely, none of the usual network monitoring tools will 
detect a duplex mismatch - although if they are both Cisco's they will 
see it with CDP and log it.  And to make this slightly relevant to 
Centos, net-snmp doesn't seem to expose the duplex setting of an 
interface if a tool did want to check.

   Les Mikesell
    lesmikesell at gmail.com