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Cisco Nexus 5548UP Link is not connected


I am trying to connect two Cisco Nexus 5548UP switches together using GLC-SX-MMD with multimode fiber but link is still down. Set the interface speed to 1000 and swap the SFP to other slot but result is still down. Kindly help me. Output is below

Switch-A# show int ethernet 1/31 brief

Ethernet      VLAN    Type Mode   Status  Reason                   Speed     Port
Interface                                                                    Ch #
Eth1/31       1       eth  trunk  down    Link not connected         1000(D) --
Switch-A# show int ethernet 1/31 capabilities
  Model:                 N5K-C5548UP-SUP
  Type (SFP capable):    10Gbase-(unknown)
  Speed:                 1000,10000
  Duplex:                full
  Trunk encap. type:     802.1Q
  Channel:               yes
  Broadcast suppression: no
  Flowcontrol:           rx-(off/on),tx-(off/on)
  Rate mode:             none
  QOS scheduling:        rx-(6q1t),tx-(1p6q0t)
  CoS rewrite:           no
  ToS rewrite:           no
  SPAN:                  yes
  UDLD:                  yes
  Link Debounce:         yes
  Link Debounce Time:    yes
  MDIX:                  no
  Pvlan Trunk capable:   yes
  TDR capable:           no
  FabricPath capable:    yes
  Port mode:             Switched
  FEX Fabric:            yes

Switch-A# show int ethernet 1/31 cable-diagnostics-tdr

Interface      Speed Pair Cable Length   Distance to fault   Channel Pair Status
-------------- ----- ---- -------------- ------------------- ------- -----------

Switch-A# show int ethernet 1/31 transceiver calibrations
    transceiver is present
    type is SFP-1000BASE-SX
    name is CISCO           
    part number is FTLF8519P3BNL-CS
    revision is A   
    serial number is FNS175111EN     
    nominal bitrate is 1300 MBit/sec
    cisco id is --
    cisco extended id number is 4

                SFP Internal Calibrations Information
                Slope  Offset      Rx4/Rx3/Rx2/Rx1/Rx0
    Temperature     0      0
    Voltage         0      0
    Current         0      0
    Tx Power        0      0
    Rx Power                       0.0000/0.0000/0.0000/0.0000/0.0000

Switch-A# show int ethernet 1/31
Ethernet1/31 is down (Link not connected)
 Dedicated Interface
  Hardware: 1000/10000 Ethernet, address: 002a.6aa3.37c6 (bia 002a.6aa3.37c6)
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec
  reliability 0/255, txload 1/255, rxload 1/255
  Encapsulation ARPA
  Port mode is trunk
  auto-duplex, 1000 Mb/s, media type is 10G
  Beacon is turned off
  Input flow-control is off, output flow-control is off
  Rate mode is dedicated
  Switchport monitor is off
  EtherType is 0x8100
  Last link flapped never
  Last clearing of "show interface" counters 00:54:36
  30 seconds input rate 0 bits/sec, 0 packets/sec
  30 seconds output rate 0 bits/sec, 0 packets/sec
  Load-Interval #2: 5 minute (300 seconds)
    input rate 0 bps, 0 pps; output rate 0 bps, 0 pps
    0 unicast packets  98 multicast packets  0 broadcast packets
    98 input packets  720 bytes
    0 jumbo packets  0 storm suppression bytes
    98 runts  0 giants  0 CRC  0 no buffer
    98 input error  0 short frame  0 overrun   0 underrun  0 ignored
    0 watchdog  0 bad etype drop  0 bad proto drop  0 if down drop
    0 input with dribble  0 input discard
    0 Rx pause
    0 unicast packets  0 multicast packets  0 broadcast packets
    0 output packets  0 bytes
    0 jumbo packets
    0 output errors  0 collision  0 deferred  0 late collision
    0 lost carrier  0 no carrier  0 babble 0 output discard
    0 Tx pause
  0 interface resets


6 Replies 6

Waqas Butt



It seems you are able to transmit successfully from Switch A, can you send across the log for Switch-B (Interface details)




Zar Ni Lay Thwin



           Remove transceiver from that port and issue command " default interface  ethernet 1/31"

And set the speed to 1000 " speed 1000 " and insert your transceiver into the port. After that configure the trunk configuration on that port.


let me know if it works.



Issue has been resolved  as the fiber cable was faulty. After replacing the cable the issue has been resolved. Thanks for your support.

Hi, how did you solve it?


I have the same issue :


HCSN5KLONEQ1# show int Eth1/28 brief

Ethernet VLAN Type Mode Status Reason Speed Port
Interface Ch #
Eth1/28 1 eth trunk down Link not connected 10G(D) 21



Jose Zapata

I just saw the cable was faulty :)
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