Network Bottlenecking

145 pts.
Tags:
Network monitoring
Network performance
How can I monitor the network for bottleknecking. Every Monday and/or tuesdays our network is so slow. Is there a way I can pinpoint what going on here? Free tools?

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Is there a specific time that your network slows down? Do you share your connection with other businesses in the building?

You may also want to check into changing your passwords for wireless access, one of the previous employees here was connecting to our wireless system from his home via a cantanna after he was let go and using the bandwidth here to play WoW -.-

There may be monitoring software already configured in your firewall or router pending on what hardware you are using.

http://www.spiceworks.com/ Has a free trial that you can run that is supported by their forums.

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A few things to consider:

1. Malicious software – are machines infected and downloading payloads?
2. Application updates being downloaded.
3. Mis-matched speed/duplex settings. This might only show up during periods of higher utilization. Check switch ports for error counters incrementing. You do have a switched network architecture, right? If not, remove any hubs and replace them with switches. Again, make sure the links are set to appropriate speed with full duplex.
4. Is this a DSL or cable link? If it is, remember that this is a shared bandwidth architecture. The carrier (ISP) may have significantly oversubscribed their network and may not be able to deliver the bandwidth you expect. You should review the SLA with your provider for the language about delivered capacity vs normal usage capacity. If you do enable QOS at your network edge, remember that the provider may not “honor” the tags that the Cisco boxes put on the traffic. It’s just something to be aware of and not of major concern. Maybe your provider can provide usage reports, request them. They are worth getting to show what is being delivered at the price you are paying.
5. Perform some network analysis. Place a network tap between the router and the LAN. See my <a href=”http://itknowledgeexchange.techtarget.com/it-trenches”>blog series on using a network tap</a>. Get a spare computer and install <a href=”http://www.ntop.org/”>ntop</a> and attach to the network tap port. It will give you the ability to see what all IP traffic is going across the link. It won’t show other protocols very easily though. You may need to use <a href=”http://www.wireshark.org/”>Wireshark</a> to see other issues on the network.

Here’s a blog entry on <a href=”http://itknowledgeexchange.techtarget.com/it-trenches/network-speed-capacity-are-not-the-same/”>Network speed & capacity are NOT the same</a> that may also help with your understanding of the network and potential capacity/speed issues.

See this similar <a href=”http://itknowledgeexchange.techtarget.com/itanswers/network-speed-slow-down-over-distance-and-time-upgrades-needed-revised/”>question and answer</a>.

Good luck & let us know how it goes!

In the IT trenches? So am I – read my <a href=”http://itknowledgeexchange.techtarget.com/it-trenches”>IT-Trenches blog</a>

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  • JennyMack
    Moderator Note: I have added comments below from Jsuarez which were submitted in a new question. Jsuarez: In the future, please include all follow-up comments in the "Discussion" section of the original question. Thanks! We have a Sonic wall 2040 pro firewall >>3690G switch >2x 2960G switches. Everyone keeps complaining about the slowness when they are opening outlook or just working off the network. We have a for our ISP SDSL line 1.1 U/D. This is a Museum so there is a lot of data that usually gets accessed here. How can I pinpoint what is going on and give my boss an overview as to why this is happening.
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  • Jsuarez
    Take a look at server performance metrics also. Check antivirus settings on both the clients and servers. Be sure backups are not happening during working hours. There are a lot of things that can cause slow client performance and you just have to chip away at the layers. This is where the OSI 7-layer model comes in handy and you should familiarize yourself with it to become a good IT staff member. Read the entire section shown at the link above. Post more about what troubleshooting steps you have taken and their results and we will be glad to assist further.
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  • Jsuarez
    I believe the issues lies with RPC. I found this @ technet. http://technet.microsoft.com/en-us/library/cc540454.aspx I am just getting adjusted to the exchange server. Put the problem discussed in this article are the problems we are having.
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  • BlankReg
    I would recommend that you first do some benchmarking when the network is definately not busy (evening/weekend). Check and measure response times across the network, and to all of the servers, and services available. Repeat this when it is moderately busy, and also when you get the reports that is bad. Even just a PING and a quick login to a service will give you some figures that let you know what is 'normal' or not. By comparing the results, you can help to narrow down if it is a network issue, or a server/service issue. If some devices still respond at about the same times, then it is probably not a major network issue, if they take a lot longer then there is some congestion. If some servers respond well, and others not, then that also narrows down the posibilites. Having a good (accurate) network diagram can help to highlight possible bottlenecks, and allows you to target the use of the tools that the other guys were talking about. Do some simple checks first, and you can save a lot of time later :-)
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  • Kevin Beaver
    I was contacted by a client recently for slow connection between their LAN and the Internet and it ended up being users who were streaming audio and video on the network combined with a slow/mis-matched Internet connection (T1 for 200+ users). There was also a suspect system that was running some malware and another with an exploitable vulnerability via the Internet that were contributing to the problem. Whether it's internal only or internal-external (like above) you need a network analyzer to see what's happening. I recommend OmniPeek because it's very easy to use and has what's called "monitor mode" where it will monitor traffic patterns, top talkers, network errors, and so on without you ever having to capture a single packet. Keep in mind that when it comes to network analyzers you get what you pay for.
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