2 Replies Latest reply: Jul 19, 2007 12:01 PM by jweiner RSS

Receive Discards on Switch uplinks

Before someone mentions it, let me say that I already did a search for "discards" on the forum and did not find anything relating to my issue.


With that said, I am using SW Engineer Toolset v9, Network Performance Monitor, and am seeing millions of receive discards on 3 of 7 ports which are active on a Cisco 3508.  All 7 active ports are uplinks to other Cisco switches - not connections to servers that might be congested or to routers or firewalls.  4 ports that uplink to other Cisco switches have no problems (no errors reported), 3 have millions.  I would think, if the Cisco switch is having problems keeping up with all packets it is receiving, all the ports would show some number of receive discards.


Also, to make matters more confusing, receive discards is not a statistic that the Cisco switches seem to keep track of.


Question - what might cause packets on specific uplinks to be discards, but not packets on other uplinks?


FYI, all 7 active ports on the 3508 seem to have a fairly consistent 1500-1700 packets/sec output rate.  Most have virtually no input rate (0-50packets/sec) 2 have 1500-1700 packets/sec input rate, neither of which is one of the probelmatic error filled ports.


 Any advice would be most helpful,


JW


 P.S.  CPU Utilization on the 3508 is at 35%.  Mem Ultilization is at 58%


 
  • Re: Receive Discards on Switch uplinks
    Network_Guru

     I did a search on the whole site for 'receive discards' & found the following posts which might be helpful in your situation:

     
     Re: Receive Discards

    One reason for receive discards on a switch is mismatched VLANs.
    We had this problem show up all of a sudden on a "tagged" or trunk
    port between our switches.

    Check the Configured VLANs on each switch port.
    The port with the RX discards will be "missing" a VLAN
    as compared to the other end of the trunk.
    The switch just "discards" the packets arriving on the missing VLAN.

    Once the VLANs were matched up, the discards stopped.
    • Re: Receive Discards on Switch uplinks

      I checked all switches at the facility.


      All switches have the same VTP domain.


      All switches are client (except for the main MDF switch which is server)


      All uplinks are set for trunk mode, dot1q encapsulation


      All switches have records of the same VLANs in their list.


      All uplink switch ports have the same active trunking VLANs