Switch diagnostics

Discussion in 'Computer Support' started by Japhy, Aug 10, 2006.

  1. Japhy

    Japhy Guest

    Hello,
    We have a "cheap" unmanaged Linksys switch for our 20 PC network.
    On occasion, it "locks up". Systems are all up, but no PC can ping
    another. We had the same problem with another switch that we replaced
    with the Linksys. I don't think it is an environmental problem
    (electrical, etc).

    If I buy a managed switch, is there somehow I could see the traffic
    running
    through the switch, to see if it is just getting overwhelmed with
    traffic?


    What combination of hardware/software could I use to diagnose this
    problem.
    Hopefully with free/shareware.


    Thanks!
    Japhy
     
    Japhy, Aug 10, 2006
    #1
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  2. Japhy

    John Holmes Guest

    Japhy "contributed" in 24hoursupport.helpdesk:

    > Hello,
    > We have a "cheap" unmanaged Linksys switch for our 20 PC network.
    > On occasion, it "locks up". Systems are all up, but no PC can ping
    > another. We had the same problem with another switch that we replaced
    > with the Linksys. I don't think it is an environmental problem
    > (electrical, etc).
    >
    > If I buy a managed switch, is there somehow I could see the traffic
    > running
    > through the switch, to see if it is just getting overwhelmed with
    > traffic?
    >
    >
    > What combination of hardware/software could I use to diagnose this
    > problem.
    > Hopefully with free/shareware.
    >
    >
    > Thanks!
    > Japhy
    >
    >


    Let the administrator take care of it.

    --
    Your mother was an appalling moron who farted constantly in a prison
    cell.
     
    John Holmes, Aug 10, 2006
    #2
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  3. Japhy

    Dan Evans Guest

    "Japhy" <> wrote in message
    news:...
    > Hello,
    > We have a "cheap" unmanaged Linksys switch for our 20 PC network.
    > On occasion, it "locks up". Systems are all up, but no PC can ping
    > another. We had the same problem with another switch that we replaced
    > with the Linksys. I don't think it is an environmental problem
    > (electrical, etc).
    >
    > If I buy a managed switch, is there somehow I could see the traffic
    > running
    > through the switch, to see if it is just getting overwhelmed with
    > traffic?
    >
    >
    > What combination of hardware/software could I use to diagnose this
    > problem.
    > Hopefully with free/shareware.


    SNMP polling with MRTG
    http://oss.oetiker.ch/mrtg/

    Dan





    .................................................................
    Posted via TITANnews - Uncensored Newsgroups Access
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    Dan Evans, Aug 10, 2006
    #3
  4. Japhy

    Meat Plow Guest

    On Thu, 10 Aug 2006 14:59:54 +0200, Dan Evans wrote:

    > ubject: Re: Switch diagnostics
    > From: "Dan Evans" <>
    > Newsgroups: 24hoursupport.helpdesk
    > Date: Thu, 10 Aug 2006 14:59:54 +0200
    >
    >
    > "Japhy" <> wrote in message
    > news:...
    >> Hello,
    >> We have a "cheap" unmanaged Linksys switch for our 20 PC network. On
    >> occasion, it "locks up". Systems are all up, but no PC can ping
    >> another. We had the same problem with another switch that we replaced
    >> with the Linksys. I don't think it is an environmental problem
    >> (electrical, etc).
    >>
    >> If I buy a managed switch, is there somehow I could see the traffic
    >> running
    >> through the switch, to see if it is just getting overwhelmed with
    >> traffic?


    You don't need a managed switch. I've used SMC for years on high traffic
    networks with no problems. Look at their SMCGS24.


    --
    COOSN-266-06-25794

    Pierre Salinger Memorial Hook, Line & Sinker, June 2004
     
    Meat Plow, Aug 10, 2006
    #4
  5. Japhy

    why? Guest

    On 9 Aug 2006 16:38:25 -0700, Japhy wrote:

    >Hello,
    >We have a "cheap" unmanaged Linksys switch for our 20 PC network.


    No model number?

    >On occasion, it "locks up". Systems are all up, but no PC can ping
    >another. We had the same problem with another switch that we replaced
    >with the Linksys. I don't think it is an environmental problem


    No model / make?

    >(electrical, etc).
    >
    >If I buy a managed switch, is there somehow I could see the traffic
    >running


    Ethereal / Wireshark / Analyser or other packet sniffer to see traffic.

    See old posts in 24HSHD with snmp, mrtg, ethereal for more info and
    URLs.

    >through the switch, to see if it is just getting overwhelmed with
    >traffic?


    Even an unmanaged switch usually has a link / collision / activity LED.

    Yes, as mentioned SNMP with MRTG. If you need better than 5 minute
    samples then MRTG + RRDTool + Routers2.cgi on a webswerver. That will by
    default give you bandwidth in and out of each port.

    As SNMP will give you all sorts of info, you simply find where it's
    located in the table, massage the target attributes MRTG is to read and
    you could get stuff like,

    bad / good packets / cpu % util / number of ports connected.

    There is lot of documentation / examples on MRTG on the MRTG site.

    At it's most basic, MRTG reads values using, target from interface @
    location

    Target[myswitch]: 1:public@wellfleetA

    At work we have a stack of 8 switches, each with independant uplinks,
    MRTG will tell me the total for each uplink by default. However to
    create a graph of the total uplinks for all 8, I had to manually edit
    the target line to.

    Target[myswitch]: 1:public@wellfleetA + 1:public@wellfleetB +
    1:public@wellfleetC and so on.

    >
    >What combination of hardware/software could I use to diagnose this
    >problem.
    >Hopefully with free/shareware.


    SNMP is a feature of a managed switch. The rest is free, runs on
    Unix/Linux/Windows.

    >
    >Thanks!
    >Japhy


    Me
     
    why?, Aug 10, 2006
    #5
  6. Japhy

    why? Guest

    On 9 Aug 2006 16:38:25 -0700, Japhy wrote:

    >Hello,
    >We have a "cheap" unmanaged Linksys switch for our 20 PC network.
    >On occasion, it "locks up". Systems are all up, but no PC can ping
    >another. We had the same problem with another switch that we replaced
    >with the Linksys. I don't think it is an environmental problem


    As it's 20 PCs, you unplugged each one (or 2 at a time) , depending how
    often the lockup is and with a particular PC out it didn't happen?

    Cables are all okay?

    All PCs are running at auto speed / duplex or fixed?

    Faulty NIC on 1 PC, generating bad noise on the wire?

    When you say replaced, as in returned / ditched the other switch?
    If you still have both, put 10 PCs in 1 , 10 in the other and link then
    together, maybe you will get lucky and 1 only will lock up.

    >(electrical, etc).


    Despite the other post I made, it may not help you as if you needed a
    managed switch / diag tools you would have knows this already and have
    set something up.

    >If I buy a managed switch, is there somehow I could see the traffic
    >running


    So you will be looking for what traffic? Ethereal or it's new version
    Wireshark has color syntax highlighting, and a summary of traffic etc.
    It's the sort of situation unless you know what you are looking for it
    won't mean anything to you.

    >through the switch, to see if it is just getting overwhelmed with
    >traffic?


    If it's some faulty hardware, a managed switch would usually isolate a
    port when it see lots of particular errors.

    Also a managed switch may have a web interface, some PC installable
    management tool to let you check ports for the error counters, that may
    help. However at work with 60 something switches and 3000 ports only
    twice have I seen an individual port lockup.

    Generally the only error counter, when systems move / are reconfigured
    is the duplex setting causing collisions. Generally all other error
    counters say at 0 even after 3 years. This tends to annoy managers when
    they want to blame something on a network fault.

    <snip>

    Me
     
    why?, Aug 10, 2006
    #6
  7. Japhy

    Japhy Guest

    Hello,
    Thanks for the replies. You've given me some good troubleshooting
    ideas.
    I have played around with ethereal some. I think it was only capturing
    data
    to/from the PC where it was running. Can I make it 'promiscuous', so
    it would
    see all traffic on the switch?
    I guess I would be looking for any of the following :
    1) a particular station generating an unusually large amount of
    traffic.
    2) a particular protocol generating an unusually large amount of
    traffic.
    3) Large number of errors
    4) ???

    I'll check the NIC configuration settings...good idea.
    How to isolate a bad cable???? Would a managed switch isolate
    a port to which was attached a bad cable...yes, I think so...

    We still do have the other switch, but since we got lockups on each,
    the think the
    problem lies elsewhere.

    Thanks,
    J

    why? wrote:
    > On 9 Aug 2006 16:38:25 -0700, Japhy wrote:
    >
    > >Hello,
    > >We have a "cheap" unmanaged Linksys switch for our 20 PC network.
    > >On occasion, it "locks up". Systems are all up, but no PC can ping
    > >another. We had the same problem with another switch that we replaced
    > >with the Linksys. I don't think it is an environmental problem

    >
    > As it's 20 PCs, you unplugged each one (or 2 at a time) , depending how
    > often the lockup is and with a particular PC out it didn't happen?
    >
    > Cables are all okay?
    >
    > All PCs are running at auto speed / duplex or fixed?
    >
    > Faulty NIC on 1 PC, generating bad noise on the wire?
    >
    > When you say replaced, as in returned / ditched the other switch?
    > If you still have both, put 10 PCs in 1 , 10 in the other and link then
    > together, maybe you will get lucky and 1 only will lock up.
    >
    > >(electrical, etc).

    >
    > Despite the other post I made, it may not help you as if you needed a
    > managed switch / diag tools you would have knows this already and have
    > set something up.
    >
    > >If I buy a managed switch, is there somehow I could see the traffic
    > >running

    >
    > So you will be looking for what traffic? Ethereal or it's new version
    > Wireshark has color syntax highlighting, and a summary of traffic etc.
    > It's the sort of situation unless you know what you are looking for it
    > won't mean anything to you.
    >
    > >through the switch, to see if it is just getting overwhelmed with
    > >traffic?

    >
    > If it's some faulty hardware, a managed switch would usually isolate a
    > port when it see lots of particular errors.
    >
    > Also a managed switch may have a web interface, some PC installable
    > management tool to let you check ports for the error counters, that may
    > help. However at work with 60 something switches and 3000 ports only
    > twice have I seen an individual port lockup.
    >
    > Generally the only error counter, when systems move / are reconfigured
    > is the duplex setting causing collisions. Generally all other error
    > counters say at 0 even after 3 years. This tends to annoy managers when
    > they want to blame something on a network fault.
    >
    > <snip>
    >
    > Me
     
    Japhy, Aug 10, 2006
    #7
  8. Japhy

    why? Guest

    On 10 Aug 2006 15:34:38 -0700, Japhy wrote:

    How about less top posting and reply inline where appropriate with your
    questons / answers next to the original comments.

    >Hello,
    >Thanks for the replies. You've given me some good troubleshooting
    >ideas.
    >I have played around with ethereal some. I think it was only capturing
    >data
    >to/from the PC where it was running. Can I make it 'promiscuous', so
    >it would
    >see all traffic on the switch?


    That option is on the capture dialog screem as you have used it before
    you will be aware of possible issues with enabling this mode, depending
    on drivers / NIC support. Although it's better than it used to be. (both
    the ability to turn on promiscuous mode and Ethereal)

    Also depends on the placement of the sniffer, of course , on a manged
    switch it's usually possible to span / mirror 1 port to another, like
    the uplink port.

    >I guess I would be looking for any of the following :
    >1) a particular station generating an unusually large amount of
    >traffic.


    Unless you have SNMP on each PC and MRTG collects from that, i.e. you
    don't need a managed switch.

    If you don't want to do that, than you do need a managed switch, and
    point MRTG to it.

    Ethereal , and others will give you conversation lists, sort by packets
    / bytes.

    >2) a particular protocol generating an unusually large amount of
    >traffic.


    See the Stats / Protocol Hierarchy.

    >3) Large number of errors


    Same thing, will also be flagged in the color coded detailed packet
    capture.

    >4) ???
    >
    >I'll check the NIC configuration settings...good idea.
    >How to isolate a bad cable???? Would a managed switch isolate
    >a port to which was attached a bad cable...yes, I think so...
    >
    >We still do have the other switch, but since we got lockups on each,
    >the think the
    >problem lies elsewhere.


    Hence if it's a bad NIC, the 10PCs on each switch.

    >Thanks,
    >J


    >why? wrote:
    >> On 9 Aug 2006 16:38:25 -0700, Japhy wrote:
    >>
    >> >Hello,
    >> >We have a "cheap" unmanaged Linksys switch for our 20 PC network.
    >> >On occasion, it "locks up". Systems are all up, but no PC can ping
    >> >another. We had the same problem with another switch that we replaced
    >> >with the Linksys. I don't think it is an environmental problem

    >>
    >> As it's 20 PCs, you unplugged each one (or 2 at a time) , depending how
    >> often the lockup is and with a particular PC out it didn't happen?
    >>
    >> Cables are all okay?
    >>
    >> All PCs are running at auto speed / duplex or fixed?
    >>
    >> Faulty NIC on 1 PC, generating bad noise on the wire?
    >>
    >> When you say replaced, as in returned / ditched the other switch?
    >> If you still have both, put 10 PCs in 1 , 10 in the other and link then
    >> together, maybe you will get lucky and 1 only will lock up.


    <snip>

    Me
     
    why?, Aug 12, 2006
    #8
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