I have little experience in expanding networks. Wondering whether if I can expand an existing 100Mbps network comprising of two fast Ethernet switches placed about 60m apart. What I need to do is connect a couple of workstations residing in another building which is about 90m from one of the existing switches. Is it possible to run a cat6 from the switch to the new building and install another switch there?
I'm far to lasy to read 802.1d, but I recall a 3-4-5 rule :-)
Read back in this newsgroup: from an ethernet point of view, there is no problem at all.
From a 'cabling', 'safety' and 'regulatory' point of view it is not advisable --or even prohibited-- to run such a length of copper between 2 buildings.
It is basically not that much a hard limit but a recommendation, so that the STP topology information cached in the switches does not time out in an unreasonably short time (or even before the STP BPDU actually would have arrived). Aside from that, it would actually require to have the 802.1d Spanning Tree implemented *and* activated to fall under this guideline. When using RSTP (which is far more common now) or when you know what you are doing (and are able to set your own max_age), you will not be affected.
It actually does not have any relation to round trip times of your links or the processing power of your switches. The trouble is, that the "message age" of a BPDU is increased by one at each bridge. And the sum value of the message age is subtracted from the max_age (which will be 20 seconds in most defaults) when building topology information.
There is no such rule in any of the standards. It used to be a "safe" guideline for nowdays rather antiquated equipment to stay within the boundaries of maximum propagation delays prescribed by the Ethernet standards. However, as switched networks separate collision domains, it absolutely does not apply here.
There is nothing in the standards that restrains you from having a 90m link. Actually, you might have a working unrepeated 150m copper link operating over standard ethernet equipment, if you get it right. Anything longer than 90m however would be outside of the structured cabling standards defined in the ISO/IEC IS 11801 or TIA/EIA 568 respectively.
While it is true that interbuilding links might (and often enough will) introduce problems with equalizing current between the two linked points, such links may as well work stable for years, even despite of lightning strikes.
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