Re: Cable-diagnostics don't match up / CRC Errors

joebrug · ‎10-07-2019

Noticed a bunch of errors on this interface earlier. I also noticed that the Pair's dont match up when doing a "sh cable-diag" on this interface. Is that of concern or a display bug? (2960-X)

2960X-Downstairs#sh cable-diagnostics tdr interface gi3/0/10
TDR test last run on: October 03 16:18:25

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi3/0/10  1000M Pair A     58   +/- 10 meters Pair B      Normal
                Pair B     58   +/- 10 meters Pair A      Normal
                Pair C     58   +/- 10 meters Pair D      Normal
                Pair D     58   +/- 10 meters Pair C      Normal

2960X-Downstairs#show interfaces gi3/0/10 controller
GigabitEthernet3/0/10 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 00eb.d590.928a (bia 00eb.d590.928a)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:21, output 00:00:02, output hang never
  Last clearing of "show interface" counters 3d17h
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 8000 bits/sec, 1 packets/sec
     729519 packets input, 154997258 bytes, 0 no buffer
     Received 29005 broadcasts (21028 multicasts)
     5 runts, 0 giants, 0 throttles
     6001 input errors, 3575 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 21028 multicast, 0 pause input
     0 input packets with dribble condition detected
     3059368 packets output, 1360328658 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

     Transmit GigabitEthernet3/0/10           Receive
   1805540922 Bytes                       1988104127 Bytes
     12018154 Unicast frames                 7075757 Unicast frames
     18462901 Multicast frames                232408 Multicast frames
      8946505 Broadcast frames                 79018 Broadcast frames
            0 Too old frames              1889743187 Unicast bytes
            0 Deferred frames               44917021 Multicast bytes
            0 MTU exceeded frames            6891177 Broadcast bytes
            0 1 collision frames                   0 Alignment errors
            0 2 collision frames               34041 FCS errors
            0 3 collision frames                   1 Oversize frames
            0 4 collision frames                   0 Undersize frames
            0 5 collision frames                  20 Collision fragments
            0 6 collision frames
            0 7 collision frames             3298245 Minimum size frames
            0 8 collision frames              636555 65 to 127 byte frames
            0 9 collision frames             1848026 128 to 255 byte frames
            0 10 collision frames             632311 256 to 511 byte frames
            0 11 collision frames             462144 512 to 1023 byte frames
            0 12 collision frames             558591 1024 to 1518 byte frames
            0 13 collision frames                  0 Overrun frames
            0 14 collision frames                  0 Pause frames
            0 15 collision frames
            0 Excessive collisions             19737 Symbol error frames
            0 Late collisions                   5086 Invalid frames, too large
            0 VLAN discard frames                  0 Valid frames, too large
            0 Excess defer frames                 24 Invalid frames, too small
      6783379 64 byte frames                       0 Valid frames, too small
     16031538 127 byte frames
      7692311 255 byte frames                      0 Too old frames
       932228 511 byte frames                      0 Valid oversize frames
      1084855 1023 byte frames                     0 System FCS error frames
      6903249 1518 byte frames                     0 RxPortFifoFull drop frame
            0 Too large frames
            0 Good (1 coll) frames
            0 Good (>1 coll) frames

Leo Laohoo · ‎10-07-2019

I agree. TDR don't match. Not only that, it is very, very rare to see a TDR length are all the same.
I would still say the cable is faulty, particularly the punch block at the remote end.
NOTE: I've seen this several times (on 2960S, mostly). The only explanation I can say is the pair is actually holding on "by a thread". Vibration cause the FCS to spike. In one case I've seen, the cable was taut against the A/C duct. Whenever the A/C goes on the vibration causes the cable to shake and the cable would flap (like a guitar string).

joebrug · ‎10-08-2019

hi Leo,
thanks for response. I got around to going to the desktop.. ran a cable tester on it and through the switch.. no errors with that. Took port apart, looked like it was terminated properly, nothing loose, etc. Went to desktop and realized there was a POE injector placed between wall and phone. (side note: if power goes out or we reboot Cisco switches, a good portion of our Shoretel phones have issues booting with POE, so we have to use injectors sometimes to "wake them up"). I removed the POE injector and now cable-diag shows pairs matching and haven't seen any CRC's since:

2960X-Downstairs#show cable-diagnostics tdr interface gi3/0/10
TDR test last run on: October 08 11:47:11

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi3/0/10  1000M Pair A     62   +/- 10 meters Pair A      Normal
                Pair B     62   +/- 10 meters Pair B      Normal
                Pair C     62   +/- 10 meters Pair C      Normal
                Pair D     62   +/- 10 meters Pair D      Normal
2960X-Downstairs#show int gi3/0/10
GigabitEthernet3/0/10 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 00eb.d590.928a (bia 00eb.d590.928a)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:04, output 00:00:15, output hang never
  Last clearing of "show interface" counters 00:59:09
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 8000 bits/sec, 3 packets/sec
     1650 packets input, 773224 bytes, 0 no buffer
     Received 234 broadcasts (170 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 170 multicast, 0 pause input
     0 input packets with dribble condition detected
     27997 packets output, 3825600 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

Leo Laohoo · ‎10-08-2019

Thanks for the update.