FC interface link failure

So a few hours ago I was in a rack rental lab (with the N2K/SAN add-on), when I notice that one of the FC links refuses to come up. With three others links already up, this looks like a physical layer failure for me.

I quickly open an emergency ticket, only to have it dismissed just as quickly, with what is probably the best conversation I've ever had with tech support:

[Me] "I'm getting a link failure on the link between N5K-1, fc2/2 and MDS-3, fc1/2 on rack 1. Please check cable"

[TS] "Cable is there. Check your config" 

:)

Unfortunately, I was completely unable to figure out what the problem was, so I had to continue my lab with that link down. I'm now posting the output here, in the hope that someone can tell me what I had done wrong.

The two FC links are parallel to each other (Nexus FC2/1 to MDS FC1/1, and Nexus FC2/2 to MDS FC1/2). One was up, the other wasn't. I'm posting the output from both to make the comparison easier.

 

N5K1# sh run int fc2/1-2

 

!Command: show running-config interface fc2/1-2

!Time: Sun Jan 19 10:45:08 2014

 

version 5.1(3)N2(1c)

 

interface fc2/1

  switchport speed 2000

  switchport mode E

  channel-group 51 force

  no shutdown

 

interface fc2/2

  switchport speed 2000

  switchport mode E

  channel-group 51 force

  no shutdown

 

N5K1# sh int fc2/1-2

fc2/1 is trunking

    Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)

    Port WWN is 20:41:00:0d:ec:a2:ed:80

    Peer port WWN is 20:01:00:0d:ec:26:ea:80

    Admin port mode is E, trunk mode is on

    snmp link state traps are enabled

    Port mode is TE

    Port vsan is 1

    Speed is 2 Gbps

    Transmit B2B Credit is 255

    Receive B2B Credit is 16

    Receive data field Size is 2112

    Beacon is turned off

    Belongs to san-port-channel 51

    Trunk vsans (admin allowed and active) (101)

    Trunk vsans (up)                       (101)

    Trunk vsans (isolated)                 ()

    Trunk vsans (initializing)             ()

    1 minute input rate 200 bits/sec, 25 bytes/sec, 0 frames/sec

    1 minute output rate 128 bits/sec, 16 bytes/sec, 0 frames/sec

      1733006 frames input, 3542215988 bytes

        10 discards, 0 errors

        0 CRC,  0 unknown class

        0 too long, 0 too short

      2078343 frames output, 4284165076 bytes

        0 discards, 0 errors

      1 input OLS, 2 LRR, 1 NOS, 0 loop inits

      3 output OLS, 4 LRR, 2 NOS, 0 loop inits

    last clearing of "show interface" counters never

      16 receive B2B credit remaining

      255 transmit B2B credit remaining

      0 low priority transmit B2B credit remaining

 

fc2/2 is down (Link failure or not-connected)

    Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)

    Port WWN is 20:42:00:0d:ec:a2:ed:80

    Admin port mode is E, trunk mode is on

    snmp link state traps are enabled

    Port vsan is 1

    Receive data field Size is 2112

    Beacon is turned off

    Belongs to san-port-channel 51

    1 minute input rate 0 bits/sec, 0 bytes/sec, 0 frames/sec

    1 minute output rate 0 bits/sec, 0 bytes/sec, 0 frames/sec

      0 frames input, 0 bytes

        0 discards, 0 errors

        0 CRC,  0 unknown class

        0 too long, 0 too short

      0 frames output, 0 bytes

        0 discards, 0 errors

      8 input OLS, 0 LRR, 14076 NOS, 0 loop inits

      1284 output OLS, 0 LRR, 13443 NOS, 0 loop inits

    last clearing of "show interface" counters never

 

MDS3(config)# sh run int fc1/1-2

version 4.1(3a)

 

interface fc1/1

  switchport speed 2000

  switchport mode E

  channel-group 51 force

  no shutdown

 

interface fc1/2

  switchport speed 2000

  switchport mode E

  channel-group 51 force

  no shutdown

 

MDS3(config)# sh int fc1/1-2

fc1/1 is trunking

    Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)

    Port WWN is 20:01:00:0d:ec:26:ea:80

    Peer port WWN is 20:41:00:0d:ec:a2:ed:80

    Admin port mode is E, trunk mode is on

    snmp link state traps are enabled

    Port mode is TE

    Port vsan is 1

    Speed is 2 Gbps

    Transmit B2B Credit is 16

    Receive B2B Credit is 255

    Receive data field Size is 2112

    Beacon is turned off

    Belongs to port-channel 51

    Trunk vsans (admin allowed and active) (101)

    Trunk vsans (up)                       (101)

    Trunk vsans (isolated)                 ()

    Trunk vsans (initializing)             ()

    5 minutes input rate 144 bits/sec, 18 bytes/sec, 0 frames/sec

    5 minutes output rate 168 bits/sec, 21 bytes/sec, 0 frames/sec

      2078354 frames input, 4284195300 bytes

        0 discards, 0 errors

        0 CRC,  0 unknown class

        0 too long, 0 too short

      1733017 frames output, 3542172940 bytes

        0 discards, 0 errors

      3 input OLS, 4 LRR, 1 NOS, 0 loop inits

      6 output OLS, 2 LRR, 1 NOS, 1 loop inits

      255 receive B2B credit remaining

      16 transmit B2B credit remaining

      14 low priority transmit B2B credit remaining

 

fc1/2 is down (Link failure or not-connected)

    Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)

    Port WWN is 20:02:00:0d:ec:26:ea:80

    Admin port mode is E, trunk mode is on

    snmp link state traps are enabled

    Port vsan is 1

    Receive data field Size is 2112

    Beacon is turned off

    Belongs to port-channel 51

    5 minutes input rate 0 bits/sec, 0 bytes/sec, 0 frames/sec

    5 minutes output rate 0 bits/sec, 0 bytes/sec, 0 frames/sec

      1 frames input, 152 bytes

        0 discards, 0 errors

        0 CRC,  0 unknown class

        0 too long, 0 too short

      1 frames output, 152 bytes

        0 discards, 0 errors

      0 input OLS, 0 LRR, 0 NOS, 0 loop inits

      0 output OLS, 0 LRR, 0 NOS, 1 loop inits

 

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