[vortex] duplex problems with 3c905

[ruben@nutz.nl]

On Mon, Sep 17, 2001 at 01:38:34PM +0200, Bogdan Costescu wrote:

> > It's plugged directly into a media converter, then a length of fibre,
> > then another media converter, and then a Cisco 4500M.

> I don't have experience with media conversions,

I do.

> but my common sense makes
> me believe that the media converters and the intermediate media itself has
> to support full-duplex communication in order for the whole end-to-end
> segment to be full-duplex capable. 

Completely correct. :) 

One could concoct a scheme where a 200Mbit HD link emulates a 100Mbit FD
link, but the added latency would screw up collision-detection pretty
effectively.

> Even more, my impression is that the
> media converter becomes the partner (or remote end) of the connection, so
> in fact you have 3 segments: card-converter1, converter1-converter2 and
> converter2-Cisco. 

Some do, some don't. The ones that do are generally more expensive, but also
more reliable. A dumb extender cannot signal one station that the link to
the other is down. It can only emulate a broken cable to signal problems. :)

Start tcpdump on an appropriate machine. Pull the fiber out, and ping
something on the other site before the arp-cache expires. If you get a
ICMP-destination-unreachable you have a smart bridge (ie.: a two-port switch
with a different media on the second port), if you see nothing but a timeout
you have a dumb one. Serial-numbers which look like MAC-addresses or
different MAC-addresses in the caches on either side are also tell-tale
signs.

-- 
Ruben

	Q: How many IBM 370's does it take to execute a job?

	A: Four. Three to hold it down, and one to rip its head off.