Cisco 3750 switch stack layer 2 fault ?

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  • Mal

    I am trying to troubleshoot a local connection problem on a Cisco 3750 switch stack.
    From my site (site A – separate subnet addressing to two other sites – sites B and C, these are also on their own subnets) I can ping server addresses and connect using remote desktop connection from my laptop terminal across the corporate network to the servers at sites B and C. However if I go to site C and plug in my laptop terminal (having changed the IP address to one on the local subnet), to the local 3750 switch stack (2 switches in the stack), I can ping and use remote desktop to connect to servers at site B across the corporate network. However if I try to ping and connect using remote desktop connection to the servers connected to the same switch stack as my terminal and with addresses all in the same subnet and vlan, I get the following problem:
    1) When I ping a server address in the same subnet and vlan which I can successfully ping across the network the ping replies the first time followed by the remaining three replies ‘Request Timed Out’.
    2) If I try to connect to the server using remote desktop connection, I cannot connect to the server.
    I am assured these servers could be accessed locally from a laptop plugged into the local switch stack with a suitable local subnet address in the past. There has recently been a power failure which is when the problems seemed to of stemmed from and the local switch stack is trunked out of a port to an ASA device. The servers are in a vlan on the switch stack with their own subnet and the laptop terminal address when connected locally is in this subnet. There is no port security on the switch ports and the terminal when connected to the switch shows in the MAC address table. Other laptops have been tried as well. When a server is pinged the first reply appears to show it is seen but then the connection drops and the same is true if an extended ping is run, the first reply works then all the rest are timed out. Am I right in assuming as the terminal and servers are in the same vlan and subnet, it is not a routing issue – connection can be made across the corporate network anyway, but that it is a local layer two issue on the switch stack. Is the problem to do with conflicts in the MAC address table and would clearing the MAC address table resolve this issue, or is it to do with an ARP issue, or the recent power failure and losing unsaved configuration changes or issues created through being trunked out through an ASA device? Any suggestions or pointers in the right direction to resolve this issue would be gratefully received.


    Re: Cisco 3750 switch stack layer 2 fault ?

    You can try “traceroute mac” command to check the connectivity on layer 2.
    For further details on usage of this command please take a look at the link below for your switch “3750 switch command reference”:


    Re: Cisco 3750 switch stack layer 2 fault ?

    Many Thanks for your suggestion which helped to isolate the problem to a problem with the NIC cards on the servers having to be reset after a power failure.


    Re: Cisco 3750 switch stack layer 2 fault ?

    I am glad that I can help you.

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