From: Cacca Mucca (caccamucca@gmail.com)
Date: Mon Mar 03 2008 - 03:30:22 ARST
Maybe one of the GLC-LH-SM is bad?
On Thu, Feb 28, 2008 at 3:15 AM, Jason Aarons <jaarons@hotmail.com> wrote:
> 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 GBIC S are much more
> tolerant than the single mode fibre sfp s as they were working without any
> known issues even though single mode long haul gbics across a mutli mode
> back
> bone in theory shouldn t 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 sfp s
> 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 sfp s/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.
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