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Interface Resets?

Hello -

I have some 2960x stacks that are dropping their 10g connections back to their main closets. This is a straight fiber connection to and from the main switch in the building and the edge switch drops it's connection to the main switch for about a minute to 5 minutes before coming back online by itself. On the two switches recording these issues, there are no errors on the interfaces, just a lot of interface resets. Can anybody shed some light as to why this might be occurring? Note the counters have not been cleared however, the switch has only been online for a few months.

TenGigabitEthernet1/0/1 is up, line protocol is up (connected)
  Hardware is Ten Gigabit Ethernet, address is 5067.ae62.48b3 (bia 5067.ae62.48b3)
  Description: To: 
  MTU 1500 bytes, BW 10000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive not set
  Full-duplex, 10Gb/s, link type is auto, media type is SFP-10GBase-LR
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:28, output 00:00:19, output hang never
  Last clearing of "show interface" counters never
  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 47932000 bits/sec, 7751 packets/sec
  5 minute output rate 19873000 bits/sec, 3389 packets/sec
     7158547139 packets input, 3880768818865 bytes, 0 no buffer
     Received 155085467799 broadcasts (579400050 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 579400050 multicast, 0 pause input
     0 input packets with dribble condition detected
     48840025693 packets output, 61229415186197 bytes, 0 underruns
     0 output errors, 0 collisions, 512 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



I suggest you do clear the counters to make sure the "interface resets" counter is incrementing when you are having the issue.

When you are not sure what interface counters are for you may find some information in Cisco IOS Interface and Hardware Component Command Reference.

For example, this counter for show interface GigabitEthernet means:

Number of times an interface is completely reset. This may occur if packets that are queued for transmission were not sent within several seconds. Interface resets may occur when an interface is looped back or shut down.

Not sure TenGigE have exact same behavior but it is very possible. This could mean some low-level forwarding problem which is rare in my experience.

I see this is a fibre link. Did you check optical power of the link in both directions?

Use show interface transceiver to display Rx and Tx if DOM is supported on your transceiver and hardware.

Good luck!



I have a Cisco 1921 router and this is happening inf on ge0/1. I've cleared counter and do see this specific counter only incrementing.

The interface has a Zyxel C1100Z DSL modem connected ted to it. 

It is causing a secondary VPN tunnel to build and then shut down triggering alerts for us of the tunnel building and breaking down shortly after. 


Modem's CSU timer or KeepAlive malfunction?


What say you?