Errors and Discard on Wan Link with QoS Applied

Posted on 2011-10-12
Last Modified: 2012-05-12
I have a number of remote sites connected to either T1 or DSL's which provide telephone service for those remote sites.  I have noticed after setting up Cacti/MRTG that I am getting a High number of Errors on the link.

WIll QoS enforcements cause errors or drops ?  Or is it more likely that there is an issue with the Circuit ?  
I notice that the errors seem to increase in proportion to CPU and Traffic Load.  We are still well under the link bandwidth max at all the sites.

Question by:GerryDalton
    LVL 5

    Assisted Solution

    Qos does not cause errors,
    Errors can be for CRC's (medium/carrier) and Drops caused by misconfiguration
    Run a Sniffer to see where's the problem.
    -hope helps-

    Author Comment

    OK errors I kinda suspected were really errors, how about DISCARDS ?  

    LVL 5

    Accepted Solution

    Well Discards occurs by a few situations:
    - The router has access rules
    - Virus/DoS/Boadcast/Multicast/P2P...Something is consume the routers/links resources (not just in BW also in number of packets)
    - Firewall restrictions
    - QoS Rules (priority packets are accepted over lower QoS)

    >Check logs
    >Use a Sniffer like tcpdump or whireshark
    >Also check etherape and ntop.


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