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Re: Transit LAN vs. Individual LANs

  • From: Warren Kumari
  • Date: Mon Feb 27 14:09:40 2006

On Feb 25, 2006, at 9:23 PM, Owen DeLong wrote:

--On February 25, 2006 8:09:22 PM +0000 "Christopher L. Morrow"
<[email protected]> wrote:

On Sat, 25 Feb 2006, Neil J. McRae wrote:

An argument could be made for individual VLANs to keep things
like b- cast storms isolated.  But I think the additional
complexity will cause more problems than it will solve.
Vlans will not stop all typres of broadcast storm.

So, perhaps I missed the earlier explanation, but why use switched
segments at all? if the purpose is to connect routers to routers putting
something that WILL FAIL in the middle is only going to increase your
labor costs later :(

So, for router-router links, GE doesn't have to mean switched...
Very true.  In fact, GE is even easier because part of the GE standard
for UTP requires it to be Auto-MDI-Sensing (MDI vs MDI-X is handled
automatically in ALL compliant GE/TP interfaces).
Unfortunately it seems that not all devices actually implement MDI/MDI-X

IEE Std 802.3ab-1999, 40.4.4 (Page 93) says:
"Implementation of an automatic MDI/MDI-X configuration is optional for 1000BASE-T devices".

IEE Std 802.3ab-1999, 40.8,2 (Page 93) says:
"Although the automatic MDI-<DI-X configuration (see 40.4.4) is not required for successful operation of 1000BASE-T, is is a functional requirement that a cross-over function be implemented in every link segment to support the operation of Auto-Negotiation"

Now, seeing as Auto-Negotiation is required, it implies that automatic MDI/MDI-X is also required -- however, certain vendors seem to ignore this....


Thus, you can use
any eia-568[ab] cable, straight or crossed between them.  (Note, USOC
cables still won't work, it has to be 568a or 568b pairing)


If it wasn't crypto-signed, it probably didn't come from me.