Transit LAN vs. Individual LANs

Warren Kumari warren at
Mon Feb 27 19:08:47 UTC 2006

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

> --On February 25, 2006 8:09:22 PM +0000 "Christopher L. Morrow"
> <christopher.morrow at> 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)
> Owen
> -- 
> If it wasn't crypto-signed, it probably didn't come from me.

More information about the NANOG mailing list