[c-nsp] Strange switchport traffic problem

[Eric Van Tol]

Hi all,
I am encountering a strange problem that I don't think I've ever seen before.  I've got an ME3400-12CS switch with an 'up/up' interface that is showing no traffic on the input/output rate counters, but the 'packets output' and 'bytes output' counters are incrementing.  Also, my NMS is showing about 4-5Mb/s output on this port.  Here's the port config and 'show int' output - timestamp shows timespan and rate of increase:

interface GigabitEthernet0/2
 switchport trunk allowed vlan 50,51
 switchport mode trunk
 load-interval 30
end

switch1#clear count gi0/2
Clear "show interface" counters on this interface [confirm]
switch1#sh int gi0/2
Load for five secs: 7%/0%; one minute: 6%; five minutes: 6%
Time source is NTP, 08:08:07.812 EDT Tue Jun 17 2008

GigabitEthernet0/2 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 001e.f6d2.d902 (bia 001e.f6d2.d902)
  MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 0/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is 1000BaseLX SFP
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:01, output hang never
  Last clearing of "show interface" counters 00:00:03
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 0 bits/sec, 0 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec
     4 packets input, 280 bytes, 0 no buffer
     Received 0 broadcasts (4 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 4 multicast, 0 pause input
     0 input packets with dribble condition detected
     2188 packets output, 1583091 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     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
switch1#sh int gi0/2
Load for five secs: 8%/0%; one minute: 6%; five minutes: 6%
Time source is NTP, 08:08:11.880 EDT Tue Jun 17 2008

GigabitEthernet0/2 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 001e.f6d2.d902 (bia 001e.f6d2.d902)
  MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 0/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is 1000BaseLX SFP
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:05, output hang never
  Last clearing of "show interface" counters 00:00:07
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 0 bits/sec, 0 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec
     9 packets input, 890 bytes, 0 no buffer
     Received 0 broadcasts (9 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 9 multicast, 0 pause input
     0 input packets with dribble condition detected
     4529 packets output, 2910397 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     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

Any ideas on what this might be?  I have another port on the same switch, configured pretty much the exact same way and I'm not seeing this weirdness.

-evt