[c-nsp] LX vs LH Transceivers

[Justin Krejci]

There appears to be a fair amount of threads online about using LX and LH
together on a SMF link. I have a situation where there is a 7206VXR with an
NPE-G1 that has a LX GBIC installed that is talking via SMF to a 12000
series router to one of our providers that is using an LX transceiver. This
gigE link has been up and running happily for a while.

 

We are running into some performance issues on the 7200 when under load so
we have a 6509 sup720 3bxl. The sup720 has one sfp port and one sfp/rj45
combo port. We have one GLC-LH-SM SFP transceiver installed into the
sfp-only port but when cutting over the above mentioned link from the 7200
to the 6509 we get no eth link at all. We verified fibers are clean, light
levels are within spec and strands connected in the correct tx/rx slots on
the transceiver. A simple hard loop at the FDP causes the gig interface to
come right up on the 6509 so I know the transceiver and gig port are
producing and receiving light at a hardware level but it seemed odd this was
not working when talking to the provider's LX GBIC. 

 

Everywhere online that I could find seems to indicate LX and LH are 100%
compatible with each other and that Cisco even uses these two
interchangeably (to the dismay of some).

http://marc.info/?l=cisco-nsp
<http://marc.info/?l=cisco-nsp&m=120612428712150&w=2> &m=120612428712150&w=2

http://en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE-LX

 

 

When talking with this provider they are adamant that their Cisco LX
equipment is not at all compatible with regular Cisco LH equipment and
mentioned that they are not using standard IOS but are using some customized
OS on their Cisco which is why there is this incompatibility. This to me
seems very suspicious like they don't want to troubleshoot this problem but
I can't dismiss their claims as invalid since I am not real knowledgeable in
this regard. They also claim they are not able to support LH connectivity
for this circuit due to this compatibility. From what I've read it seems the
LH/LX compatibility is really more of a hardware difference and software
driving the hardware would have no real bearing on this but again I don't
have anything to back up my line of thought. Do I need to press my provider
a little harder on this issue or are their claims true/possible and I am
just going to have to get an actual "LX" SFP for this circuit or figure
something else out.

 

Thanks!

Justin Krejci