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Understanding why an optic sees Rx Power but does not bring up Link



  • I have a 1000Base-LH transceiver (Cisco GLC-LH-SMD) which sees Receive Power and brings up link when inserted into several devices … but does not bring up link when inserted into several other devices
  • This is novel behavior to me:  Would anyone have a model to offer for why?



  • In each case, I remove the GLC-LH-SMD from the original device and insert it into the listed device
  • Link Comes Up
    • Fluke LinkRunner:  successfully pings the default gateway, DNS server, and
    • Netscout Optiview XG:  successfully captures and sees ARP Requests from the far side
  • Link Stays Down
    • NetAlly Linkrunner 10G
    • Cisco Nexus 93180YC-EX (aka 'N9K’ in the output below:  this is the device where I want the GLC-LH-SMD to work)
    • Cisco Catalyst 2960X


  • The diagnostics on the optic report Rx Power:


N9K# sh int eth1/13 transceiver details


    transceiver is present

    type is 1000base-LH

    name is CISCO

    part number is TRPUG1CLXECISE2G

    revision is 01

    serial number is OPM23170SHM

    nominal bitrate is 1300 MBit/sec

    Link length supported for 9/125um fiber is 10 km

    cisco id is 3

    cisco extended id number is 4

    cisco part number is 10-2625-01

    cisco product id is GLC-LH-SMD

    cisco version id is V01


           SFP Detail Diagnostics Information (internal calibration)


                Current              Alarms                  Warnings

                Measurement     High        Low         High          Low


  Temperature   38.06 C        89.00 C     -9.00 C     85.00 C       -5.00 C

  Voltage        3.29 V         3.59 V      3.00 V      3.50 V        3.09 V

 Current       21.63 mA       69.90 mA     4.50 mA    64.95 mA       5.50 mA

  Tx Power      -6.25 dBm       0.99 dBm  -13.56 dBm   -3.00 dBm     -9.50 dBm

  Rx Power      -9.24 dBm       0.99 dBm  -23.01 dBm   -3.00 dBm    -19.20 dBm

  Transmit Fault Count = 0


  Note: ++  high-alarm; +  high-warning; --  low-alarm; -  low-warning




N9K# sh int eth1/13 status



Port          Name               Status    Vlan      Duplex  Speed   Type


Eth1/13       To CTL             notconnec 2001      auto    auto    1000base-LH



  • I inserted a Fluke SimpliFiber Pro and measured -9.23 dBm at 1310nm Receive Power



  • This pathway services a flat-rate 1G Commercial Internet service rented from a carrier (the service is marketed as 'Internet IQ').  We rent (2) of these services.
  • The service has worked  all year … but @ 1:20am PDT on Tuesday 9/14, these (2) 'Internet IQ' services went down.  The other service returned to life ~20 minutes later; this one did not.  I’m working a ticket with the carrier; they reported finding a problem on their end and ‘reset a router port’, which sounds promising but hasn't helped
  • The carrier reports that their Ethernet gear is a Juniper MX960



Stuart Kendrick

2 Replies 2

VIP Community Legend VIP Community Legend
VIP Community Legend

Couple of testing :


1. try adding command - speed nonegotiate

config t

interfface eth x/x

speed nonegotiate

shut and no sut bot the sides


2. Try to twitst Fible lead










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I would agree with speed nonegoiate being a feature needed some times. Have seen this ALOT with ASR9k 1000nv Satellite pannel -> ASR920 with 1G LX SFPs! Have to add/ remove the command on the correct side to get it to work, some times it is opposite of what we did last time

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