Need help troubleshooting CRC errors

Discussion in 'Cisco' started by pfisterfarm, Sep 17, 2009.

  1. pfisterfarm

    pfisterfarm Guest

    Some of our older remote sites are connected via ATM. Two or three T1s
    come into an Cisco 8510, and from there a 155mbps OC3 connection over
    fiber to a 3640 router. Lately, I've been noticing that pretty much
    every one of them is showing what I think is a rather high receive
    error count on the 3640 end of the OC3 connection, and it all seems to
    be CRC errors. Not much of any errors are showing up on the 8510 end
    of the OC3 connection. For example, one site yesterday late afternoon
    showed 63, 763 receive errors for the day. Several others were in the
    20Ks. I'm not really certain what the cause might be, or where to
    start. Can anyone help?

    Thanks!
    pfisterfarm, Sep 17, 2009
    #1
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  2. pfisterfarm

    Thrill5 Guest

    The transmit fiber on the 8510 is probably having an issue. Since this is
    OC3, I'm going to assume that the fiber has been in place for quite a long
    time. Could be as simple as some dust and you just need to use a can of air
    to clean everything out, or it could be a bad connector and you need to
    reterminate one or both ends. The glues that were used way back did not
    hold up over time and would eventually fail. Could also be faulty optics on
    either the transmit or recieve. You can try swapping the trasmit and
    receive on both ends and if you see the errors on the 8510, then you
    definately have a fiber problem. If you still see errors on the 3640, then
    its probably with the transmit optics on the 8510.


    "pfisterfarm" <> wrote in message
    news:...
    > Some of our older remote sites are connected via ATM. Two or three T1s
    > come into an Cisco 8510, and from there a 155mbps OC3 connection over
    > fiber to a 3640 router. Lately, I've been noticing that pretty much
    > every one of them is showing what I think is a rather high receive
    > error count on the 3640 end of the OC3 connection, and it all seems to
    > be CRC errors. Not much of any errors are showing up on the 8510 end
    > of the OC3 connection. For example, one site yesterday late afternoon
    > showed 63, 763 receive errors for the day. Several others were in the
    > 20Ks. I'm not really certain what the cause might be, or where to
    > start. Can anyone help?
    >
    > Thanks!
    Thrill5, Sep 18, 2009
    #2
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  3. pfisterfarm

    pfisterfarm Guest

    I have a little more detail about the problem now:

    'show atm pvc x/y' shows:

    CrcErrors: 69402, SarTimeOuts: 2, OverSizedSDUs: 0, LengthViolation:
    69294, CPIErrors: 0

    Also, the router side shows, on 'show int':

    MTU 1500 bytes, sub MTU 1500, BW 155000 Kbit, DLY 80 usec,

    router side, on 'show atm int atm':

    Max. Datagram Size: 1558

    8510 switch side, on 'show int':

    MTU 4470 bytes, sub MTU 4470, BW 155520 Kbit, DLY 0 usec,

    Would this be a problem?
    pfisterfarm, Sep 18, 2009
    #3
  4. On Sep 17, 4:32 pm, pfisterfarm <> wrote:
    > Some of our older remote sites are connected via ATM. Two or three T1s
    > come into an Cisco 8510, and from there a 155mbps OC3 connection over
    > fiber to a 3640 router. Lately, I've been noticing that pretty much
    > every one of them is showing what I think is a rather high receive
    > error count on the 3640 end of the OC3 connection, and it all seems to
    > be CRC errors.


    If you look at the outputs from 'sh controller T1 X/Y' on the 3600
    series, do you see FEBE (Far End Bit Error), LCV (Line Code
    Violations) or PCV (Path Code Violations) counters increment ? If it's
    Path code, I'd point my finger towards the 8510, or the transport
    network, If it's Line code, then it's most likely local (to the 3600)
    cabling.


    >Not much of any errors are showing up on the 8510 end
    > of the OC3 connection. For example, one site yesterday late afternoon
    > showed 63, 763 receive errors for the day. Several others were in the
    > 20Ks. I'm not really certain what the cause might be, or where to
    > start. Can anyone help?
    >
    > Thanks!


    Have a read over this doc:
    http://www.cisco.com/en/US/tech/tk713/tk628/technologies_tech_note09186a00801095a3.shtml#topic1
    , it'll outline what the counters on 'sh controller t1' mean, then you
    can step it up to this doc (Mostly specific to the PA-A3, however the
    counters mean the same on every controller, they're just might be
    called something else) :
    http://www.cisco.com/en/US/products...oducts_tech_note09186a00800d76fb.shtml#topic2

    Keep an eye on which counters are incrementing, and at which rate
    (hint, use 'ter exe pr t' to put a timestamp at the top of every show
    command).

    Regards,
    Ruairi
    Ruairi Carroll, Sep 21, 2009
    #4
  5. pfisterfarm

    Thrill5 Guest

    Yes the MTU could mismatch could be the problem. Set the MTU on the 8510 to
    1500 using the command "mtu 1500" on the sub interface.


    "pfisterfarm" <> wrote in message
    news:...
    >I have a little more detail about the problem now:
    >
    > 'show atm pvc x/y' shows:
    >
    > CrcErrors: 69402, SarTimeOuts: 2, OverSizedSDUs: 0, LengthViolation:
    > 69294, CPIErrors: 0
    >
    > Also, the router side shows, on 'show int':
    >
    > MTU 1500 bytes, sub MTU 1500, BW 155000 Kbit, DLY 80 usec,
    >
    > router side, on 'show atm int atm':
    >
    > Max. Datagram Size: 1558
    >
    > 8510 switch side, on 'show int':
    >
    > MTU 4470 bytes, sub MTU 4470, BW 155520 Kbit, DLY 0 usec,
    >
    > Would this be a problem?
    Thrill5, Sep 22, 2009
    #5
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