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How to see unknown protocol drops on 2811 Router

I have an issue where UDP packets are constantly being dropped through a 2811 router.  When I do a show vlan 600 I get the following:

Vlan600 is up, line protocol is up
  Hardware is EtherSVI, address is 0025.84fb.7590 (bia 0025.84fb.7590)
  Description: Cisco Management Segment
  Internet address is
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 2/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 1w6d
  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 1037000 bits/sec, 176 packets/sec
  30 second output rate 57000 bits/sec, 78 packets/sec
     198077267 packets input, 2636187411 bytes, 0 no buffer
     Received 12450725 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     88773918 packets output, 3948583617 bytes, 0 underruns
     0 output errors, 0 interface resets
     95053 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out

The counter continually increases.  I tried to setup a span session with the VLAN on the Router, but got the following:

(config)#monitor session 1 source vlan 600
SPAN Source Vlan is not supported in this platform

IOS: Version 12.4(15)T9

How can I find out why these packets are being dropped?



Unknown protocol drops reports the packets with unknown or un-configured protocol on a per interface basis.

If the router reports unknown protocols, this means that if the router interface is running IP, then it received e.g IPX beside the IP packets... so it drops it, because this protocol is not running on the interface... anyways.. this has something to do with the network and PCc connected... it is nothing major..

You can use a sniffer to identify the unknown protocol.

Hope this clear you.

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