Showing results for 
Show  only  | Search instead for 
Did you mean: 
New Contributor

Input errors and CRC errors on interfaces

I am seeing input and CRC errors on WAN interface at one of branch router. Topology overview is :   WAN----> Adtran 3430 (eth 0/1) -------> Juniper 2200 (LAN via eth 0/2).

We are using site to site VPN at this router.

Interface configuration:

show run int eth 0/1

Building configuration...



interface eth 0/1

  description Spectrum IP is ************

  speed 100

  ip address  ***************

  ip access-policy Public

  ip crypto map VPN

  no shutdown

  no lldp send-and-receive



Here is details output for interface:

sh int eth 0/1        

eth 0/1 is UP, line protocol is UP

  Description: Spectrum IP is ************

  Hardware address is **************

  Ip address is **********, netmask is

  IP MTU is 1500 bytes

  BW is 100000 Kbit

  100Mb/s, full-duplex

  ARP type: ARPA; ARP timeout is 20 minutes

  Last clearing of "show interface" counters: 02:51:50

  5 minute input rate 138080 bits/sec, 29 packets/sec

  5 minute output rate 72320 bits/sec, 36 packets/sec

    Queueing method: fifo

    Output queue: 0/256/0 (size/max total/drops)

    Interface Shaper: NOT ENABLED

    426676 packets input, 238919227 bytes

    426620 unicasts, 56 broadcasts, 0 multicasts input

    0 unknown protocol, 0 symbol errors, 0 discards

    3731 input errors, 0 runts, 0 giants

    0 no buffer, 0 overruns, 0 internal receive errors

    0 alignment errors, 3731 crc errors

    463362 packets output, 131887741 bytes

    463362 unicasts, 0 broadcasts, 0 multicasts output

    0 output errors, 0 deferred, 0 discards

    0 single, 0 multiple, 0 late collisions

    0 excessive collisions, 0 underruns

    0 internal transmit errors, 0 carrier sense errors

    0 resets, 0 throttles

Please suggest me some troubleshooting tips.

0 Kudos
1 Reply
Honored Contributor
Honored Contributor

Re: Input errors and CRC errors on interfaces

You probably have a duplex mismatch. When you specify "speed 100" that turns off auto-negotiation. The other side will then fall back to half-duplex. I would suggest that you remove the "speed 100" statement in the interface configuration. This will probably cause the interface to bounce. Then clear counters and see if the errors continue to increment.

If this doesn't fix it or the interface doesn't recover, you may need to use a crossover cable if the other side doesn't do auto-MDI-X.

If it still doesn't want to behave, you may need to go to the connected device on eth 0/1 and configure both sides to 100Mbits and full duplex. I bet simply removing the "speed 100" statement will fix it.

config t

interface eth 0/1

no speed 100


clear counter eth 0/1

show int eth 0/1

[wait a couple of minutes]

show int eth 01

Look for incrementing errors.