Can I used a managed switch to tell if the comms loss is another switch or a NIC?

Discussion in 'Networking & Security' started by ICE_9, Apr 5, 2018.

  1. ICE_9

    ICE_9 2[H]4U

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    Work related issue I am trying to solve. A network port keeps losing comms for 3-6 seconds and it screws up my tool. I have had all the cables replaced, new ports, even a new computer installed. Only common thing is the switch that it connects to.

    Their box shows the comms loss but they blame the comms loss on my tool. My tool shows solid connection. I am thinking of putting a managed switch between their box and mine to see if it can tell me where the loss is coming from. Suggestions?
     
  2. Cmustang87

    Cmustang87 [H]ardness Supreme

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    What kind of gear is connected to what?

    Do they participate in SNMP? CDP/LLDP?
     
  3. ICE_9

    ICE_9 2[H]4U

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    Switch to Port. Port to NIC. Static IP. Port security enabled. That is all I really am allowed to know.
     
  4. Cmustang87

    Cmustang87 [H]ardness Supreme

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    What tool are you using and what kind of switch is this device connected to is what I'm asking about?
     
  5. MikeRotch

    MikeRotch Limp Gawd

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    You don't need managed switch, you need a packet sniffing tool. Something like Wireshark.
     
  6. Cmustang87

    Cmustang87 [H]ardness Supreme

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    How frequently is the switch port going down? MikeRotch is right, but unless you can communicate with that VLAN/Subnet, wireshark could be tricky. You can place devices inline/TAP and view the traffic as well. Could be tons of variables here, STP, port negotiation, broadcast storm, etc.
     
  7. Kelter

    Kelter Limp Gawd

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    A manage switch would definitely make this easier plus would probably have logs detailing if the port actually flapped and if so, why if it is something on the switch side. Otherwise ya, could use tcpdump/wireshark if your device supports it.. if not, again, a managed switch would come in handy.. could span the port off to another host which does support tcpdump/wireshark and get your capture that way, although it will only be at the switch side, and ideally you would want both the switchside and client side traces.
     
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  8. ICE_9

    ICE_9 2[H]4U

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    So the IT guys I think have some packet sniffing thingy they hooked up in line. As soon as they did, it errored out a lot. We replaced the network cable from the box to the network port in the floor and it stopped. They walked away saying it was fixed 2 hours later. Same exact issue has came back just a couple days later and they will not come back out as "we fixed it" is their answer.

    Frequency is really random. It usually stays down for 3-6 seconds on average. Some days it will happen 3 times that day. Others it will be on the order of about every 10 minutes. I think it personally is the house switch. I got a call this weekend and they replaced the computer again while I was gone to appease the engineer. I will be monitoring it this weekend myself for errors again.

    There are other computers on the network that have the same issue just to a much lesser extent. Some have never had the problem at all. Realize when I say network, we are talking a major company network with a massive order of network connections.
     
  9. Cmustang87

    Cmustang87 [H]ardness Supreme

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    This reeks of a network loops/spanning tree problem and/or port negotiation/mismatch problem.
     
  10. Stoly

    Stoly [H]ardness Supreme

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    Its possible that there are other pcs that are affected but don't notice the problem.

    I had a similar problem a few years back, a couple of pcs would randomly disconnect from the network. Long story short, I discovered that 4 ports on the switch went bananas.
    In fact I still use that switch (in the service area). Its a 24port SMC Tigerstack IIRC. Now it only has 8 fullly working gigabit ports and the rest either work at 100mb, randomly disconnect or not work at all.
     
  11. Kelter

    Kelter Limp Gawd

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    It could just be that your patch panels/network drops in the cubes are bad. Have you tried connecting directly into the switches?
     
  12. ICE_9

    ICE_9 2[H]4U

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    Well, I can't connect directly into the switch due to distance. This is a manufacturing environment and the switch is on a different floor. Either way, the new box was configured and low and behold, their switch started detecting the drop outs! Now we are in the process of a new TO drop to see if this resolves the issue.
     
  13. Dead Parrot

    Dead Parrot [H]ard|Gawd

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    To answer the OP's original question, yes if the smart switch keeps logs. Connect port 1 to upstream device. Connect port 8 to your tool. When the drop happens, if the switch shows port 1 went down, upstream problem. If port 8, it is your tool or the connecting cable. If the switch reboots, power problem.