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Unknown protocol Drops on 3900 router

Unanswered Question
Dec 30th, 2013
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can someone explain why i am seeing unknown protocol drops on the interface and also unknown media type detected and this is a MPLS WAN interface.


GigabitEthernet0/0 is up, line protocol is up

Hardware is PQ3_TSEC

  MTU 1500 bytes, BW 20000 Kbit/sec, DLY 100 usec,
  reliability 255/255, txload 25/255, rxload 49/255

  Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set

  Keepalive set (10 sec)

  Full-duplex, 100Mb/s, media type is unknown media type

  output flow-control is unsupported, input flow-control is unsupported

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters 01:15:00

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 38

  Queueing strategy: Class-based queueing

  Output queue: 0/1000/0 (size/max total/drops)

  5 minute input rate 3910000 bits/sec, 579 packets/sec

  5 minute output rate 1976000 bits/sec, 475 packets/sec

     2045331 packets input, 1515620832 bytes, 0 no buffer

     Received 154 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 151 multicast, 0 pause input

     0 input packets with dribble condition detected

     1783756 packets output, 1109751258 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     151 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


Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.0(1)M1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
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sh run int gig0/0
Building configuration...

Current configuration : 208 bytes
interface GigabitEthernet0/0
description ATT MPLS Circuit ID: xxxxxxxxxxxxxxx

bandwidth 20000
no ip address
ip nbar protocol-discovery
duplex full
speed 100
max-reserved-bandwidth 100

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John Blakley Mon, 12/30/2013 - 13:02
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Unknown protocol drops are anything that the router doesn't understand. The most common cause is DTP frames from the switchport. If you turn negotiation off and clear counters, you may see that they're not incrementing any longer.


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SACHIN SHARMA Tue, 12/31/2013 - 05:58
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John ,

this interface is a uplink to service provider WAN router, we dont know what is the device connected on their side?



John Blakley Tue, 12/31/2013 - 06:59
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Not sure. Is this an ethernet handoff to an ATT switch? If so, you may have to contact them to see if they can turn negotiation off.


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Richard Burts Tue, 12/31/2013 - 07:27
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From the fact that there is no IP address configured on the physical interface and from this line in the output of show interface

Encapsulation 802.1Q Virtual LAN, Vlan ID  1

I believe that we can be quite confident that the router is connected to some type of Ethernet switch. Therefore it is somewhat likely that the unknown frames are DTP.




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