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Wired Networks Thread, Switch Problem? in Technical; Hi folks, Firstly, excuse my naivety when it comes to switches. I know very little about them. We've had an ...
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    Gongalong's Avatar
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    Question Switch Problem?

    Hi folks,

    Firstly, excuse my naivety when it comes to switches. I know very little about them.

    We've had an ongoing problem in one particular IT classroom where the network is anecdotally often very slow, and gets worse and worse over a period of time (typically months).

    Today was the first chance I've had to look at the problem properly, and been able to reproduce it e.g. websites taking 20-30 seconds to open, whereas elsewhere in the school they were opening normally.

    I checked PCM and there was no load on the classroom’s switch, nor the web filter/Internet. I pinged the web filter, and it showed a solid <1ms response with no packet loss. I rebooted the switch, and everything went back to normal i.e. was quick.

    The switch itself is a 3Com 5500-48 (model no. JE103A, ROM = 2.02, SW Version = 3.02.03s56), which anecdotally is around 6-7 years old.

    I was curious as to whether this highlights a problem with the switch and it should just be replaced, or whether it’s expected to need to reboot these every few months?

    TIA

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    sonofsanta's Avatar
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    Shouldn't need to reboot it, we had a 24-port 500G at the core of our network until a year ago and it didn't display that issue.

    With websites being slow to load - is it just sitting at a blank screen for 20 seconds then loading in a rush? That's been a DNS issue for me in the past, though how it's happening here I don't know.

    I can only think it's the ARP table getting overwhelmed, althought the 5500 is a high enough spec switch that it shouldn't be a problem. Next time it's an issue (however long that may be ), instead of rebooting the switch, telnet in and type
    reset arp all
    Delete all entries when asked. It will build itself up again as traffic moves through the switch. If performance picks up again, you know that's the issue, although I've no idea why it would be happening.

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    Gongalong (2nd May 2013)

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    cpjitservices's Avatar
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    Has this always been the case or has it been happening a while ? Have you added more devices to the switch ? Does sound like an ARP table getting full or the RAM is going iffy, you could maybe try a firmware update if you havent already got the latest.

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    Gongalong (2nd May 2013)

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    Gongalong's Avatar
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    sonofsanta: yes, blank browser for about 20-30 seconds, then the page will load. It doesn't load instantly as such, but it isn't slow to then load. This was using both IE and Chrome.

    I wasn't getting any obvious slow down with file transfers, but then it's hard to say whether that's a problem or not. PING certainly wasn't showing any packet loss.

    I'll try the reset arp next time.

    cpjitservices: it sounds like it predates me, and I've been here almost 2 years. The number of devices on the switch hasn't changed.

    I'm wary of touching the switch, but will see if I can figure out the firmware update.

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