This is one of the networking principles in fact. Interface speed can be nowadays somewhere between 64Kbit and 1Gbit (on single plain interface) - keeping it simple. One of the good things™ is interface speed auto-sensing in ethernet-based networks.
If you connect ethernet devices together, they usually come to an agreement what speed to use... If both devices are 1gbit they will probably negotiate 1gibt link speed. If you have 100mbit and 10mbit on the other side they will work at 10mbit as the faster one will tune down to be able to work with the slower device... As an addition there is a negotiation of the mode - full or half duplex which defines if both parties can speak at the same time (full duplex) or only one is sending while the second one is receiving (half duplex).
With network cards, routers and more advanced switches you can set those parameters by hand - either to force your settings or... set them by hand to avoid problems with auto-sensing.
And that's the solution... In my setup I have a fibre link with ethernet ports coming out of the kit, ethernet set to 10mbit full duplex and nothing else... I've connected Cisco Catalyst 2950 switches that support auto-sensing by default on all interfaces. This works very well if you connect a PC to it... then it's fine...
If connecting non-PC hardware to your switches, for your own sake set port speed and duplex parameters by hand. This will save you a lot of time!
As another example - Mikrotik (which is really fantastic router software - really worth checking at www.mikrotik.com) can set that very easily on network cards attached to it... but sometimes it still won't help. When I did it in Mikrotik the link was fine but still I had a lot of problems, so I introduced another device on it's way - Catalyst 2950 with 2 FastEthernet ports in one VLAN... one port took ethernet from the fibre kit, other one got Mikrotik router on it and with first port parameters set by hand all problems disappeared.
At the same time I should find it out much faster and myself... Great thanks go to Dan Goscomb for throwing an obvious question across MSN - 'Have you set port speeds and duplex manually?' :-) When I saw collision and retransmition counters on the interface on my Catalyst I was simply shocked! That was so obvious! Thanks Dan!
The whole story just proves, that sometimes in IT there is no logic at all - some devices will just not work with each other the way they should, even if they speak the same protocols. Probably it's some vendor specific issue - difference in implementation of some functions, where one has some extensions to the standard or doesn't implement part of it's requirements the way it should. This happens all the time...
The best things about the standards is that there is so many to choose from!
I wish I didn't waste a week time (including several nights and almost the whole weekend) on this stupid issue. Next time I'll set all the parameters before I start any tests :-)
Happy Easter everyone!
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