From: Jason Aarons (jaarons@hotmail.com)
Date: Thu Feb 28 2008 - 00:15:37 ARST
The issue we had on site was that the fibre connections to the newly installed
3750 switches with GLC-LH-SM would either flap or not come up at all. We were
replacing 3500Xls that had WS-G5486. Both sides had mode conditioning cables
running over multimode, that had been in production for 4 years. Are there
any known 3750 bugs, etc?
The supplied sfps/gbics were single mode long haul fibre gbics and the fibre
patch leads were mode conditioning. The site originally had single mode long
haul gbics (in most cabinets) however the patch leads were multi mode in most
cases (from memory there was one mode condition cable). This was unusual given
that the fibre backbone is 62.5 micron multimode and that the longest fibre
run was no longer than around 250m (this is from memory of reading the site
fibre audit). It would appear that the single mode GBICS are much more
tolerant than the single mode fibre sfps as they were working without any
known issues even though single mode long haul gbics across a mutli mode back
bone in theory shouldnt especially given the short distances that most
cabinets had.
The fix on the day was to use short haul multi mode sfps and gbics and multi
mode fibre patch leads. We had some extra multi mode fibre gbics and sfps and
had to purchase fibre patch leads on the day to get the site cutover. We also
had to lend customer multi mode sfps from our lab.
I believe the problem was that it was assumed, and rightly so, that because
the site had single mode long haul gbics originally, that replacing them with
a like for like setup would be ok. I would have made the same assumption,
however I had suggested through another email stream that a fibre audit would
be a good idea prior to ordering the sfps/gbics but I understand that it
would be a difficult thing to do as this may require an outage to do so.
In summary, as it is a confusing issue, the structured fibre backbone is multi
mode 62.5 micron with the longest fibre run , according to a fibre site audit,
being no longer than around 250m. This would mean that short haul gbics/sfps
with multi mode patch leads would be required and not long haul single mode as
was supplied.
This archive was generated by hypermail 2.1.4 : Sat Mar 01 2008 - 16:54:50 ARST