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Wireless Networks Thread, Network Infrastructure in Technical; Originally Posted by eduabncs Nagios is good. But for monitoring bandwith. cpu & memorey use etc MRTG is better IMHO. ...
  1. #16

    localzuk's Avatar
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    Re: Network Infrastructure

    Quote Originally Posted by eduabncs
    Nagios is good. But for monitoring bandwith. cpu & memorey use etc MRTG is better IMHO.
    I believe Cacti has replaced MRTG hasn't it?

    Cacti is a very nice tool for spotting odd network behaviour - such as 100Mb spikes on individual workstations.

  2. #17

    Geoff's Avatar
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    Re: Network Infrastructure

    No, rrdtool has replaced MRTG. Cacti simply provides a nice GUI interface to configuring and organising your graphs.

    Cacti and Nagios really aim to do different things. Where as Cacti can tell you what was happening on your network last week Nagios can tell you what is happening now. So you really need to use both tools together to get a complete overview.

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    Re: Network Infrastructure

    Quote Originally Posted by rusty155
    Thanks for all of the replies.

    Are there any good (free??!!) network monitoring tools to keep an eye on network traffic and expose bottlenecks?
    I like PRTG on Windows. The free version only gives you 3 monitors at once, but I don't think the paid-for version is expensive. Very easy to set up.

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    Re: Network Infrastructure

    If your diagram is correct it would appear to be fairly optimal for the equipment you have.
    If the 3coms are correctly stacked they should be counted as a single switch and not 3 hops. These can be trunked to improve bandwidth from core to the more populated stacks.

    I would be on the look out for broadcast traffic as you do not illustrate any routers or L3 routing switches configured you seem to be operating a single broadcast domain where one bad nic will kill the lot!

    Unless you are load balancing these servers then use perfmon to watch the disk queue lengths as it is more likely with so many end nodes and so few resources the bottlenecks could be at the disks and not at the lan at all.

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    Re: Network Infrastructure

    Ok big update i'm afraid!

    Ok!! I've been able to spend some time on this problem and have discovered the following:

    First of all, the problem that I am having is not related to MS Access at all! I has just been highlighted by it due to the apparent sensitivity of Access to network issues.

    The problem actually lies with the 3COM switches. They are all Superstack 3 4200 series switches (4226T more specifically).

    They appear, for whatever reason, to be resetting themselves approx every 10-20 minutes. This is causing the workstations attached to them to drop off the network for about 10-15 secs before they pick up an address again.

    If I try to manage the switches through a web browser, I receive the error:

    "Error in SNMP read. Failed to get system information."

    I am then prevented from viewing / changing any settings for the switch.

    If I Telnet in, I am able to view most settings, and can reset to factory defaults. I have done this, which does not reslove the problem. I am not able however to view or change any settings with regard to the IP address. If I attempt to, the following error occurs:

    "Invalid option, or combination of options selected"

    Out of 12 3COM switches, across 3 separate cabinets, this occurs on 5 switches. The strange thing is, that the switches that I can manage are uplinked to at least one other 3COM switch. That is, the problem 3COM switches are either directly linked to the core switch, or pass through a non-3COM switch before the core.

    Another strange occurance with regard to the first stack of 4 switches in the diagram is that I can get in to the management of the 2nd, 3rd and 4th switches in the stack, and thus view the stack as a whole. I am however unable to view or change the device settings of the stack - just see an overview. Within this overview, I can see the IP Address of the switch that I have pulled up through the browser, but the other switches in the stack show an IP of 0.0.0.0. This is the case for the last 3 Switches in the stack - I recieve the snmp error if I try to open up the management page of the first switch in the stack.

    I am sorry for the bombardment!! - I have been looking into this for the past couple of days with an engineer sent from RM without much success. (He has never seen or heard of anything like this before!)

    I am severely stuck at this point, and sinking increasingly out of my depth!!

    As a further note, I have contacted 3COM who only offer support for 90 days after purchase, and are only able to assist via a paid support option which I really do not want to pursue at this time!! I cannot find anything of use on their knowledgebase either!

    HELP!!

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    Re: Network Infrastructure

    Obvious things to check:

    1) Are you suffering from a network loop and thus an ARP storm? Try enabling STP. Check with a packet sniffer for excess ARP traffic.

    2) Make sure your switches are running the latest firmware. You may be the victim of a bug.

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    Re: Network Infrastructure

    Ok thanks Geoff - firmware update on all of the switches did the trick! ops:

    I thought about updating the firmware early on but thought i'd try a few other things first.

    Why would these problems suddenly happen? one day fine and the next chaos!!?? Is buggy firmware common in switches and how does it come about?

    Thanks again for all the help!

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    Re: Network Infrastructure

    This problem seems to occur on a lot of the 3com switches, you may find that it will start happening again even if you have firmware upgraded them. I hav a customer with around 30 3com switches and they have all reset at some point radom like. We think we have sorted the problem out now by putting in a aggrigation switch (4200g) using the spf slots for the fibre in and the gig ports to manage the stack rather than cascading. To put it simply the 3com switches do not work well with the cascading as they are designed to be solo / edge switches (they in theory should cascade but dont always work!). If it starts happening again i would suggest buying some of these!!!

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