Monitoring LAN traffic

Hi,

I've got a LAN with somewhere between 20-30 systems connected which has recently started running incredibly slowly.  By slowly I mean network traffic, especially related to Internet services.  I have run virus scans and they have come back clean.

I want to find some tools / software which I can install on a system within the LAN to try and establish what's causing the slowdown.  I know about Wireshark, although I'm a relative novice.  I know how to inspect the I/O graphs which will be a good starting place.

What I would really like is a piece of software which I can run, and it builds up a graphical representation of network traffic, with source & destination IPs and ports etc.  I expect this exists, but I must be Googling the wrong terminology as I can't find what I want.  I have a fairly limited budget for this, so enterprise $$ software is out of the question.

If anyone can point me in the right direction would be very grateful.
fred2k3Asked:
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
The 8ssue with monitoring LAN like you want to do is impossible by just watching traffic "silently". You'll only see broadcasts and other undirected traffic, plus specific traffic for the device running the monitoring. Because doing that is exctly what switches are used for.
It might be sufficient to get an idea of general issues like massive congestion, overly sent broadcasts aso., but you'll not see which endpoints tak to each other.

Since Internet traffic is always going thru the corresponding router, that is a good point to start with. The router might support Netflow, a protocol you can use to get network metrics collected and sent to a monitoring software or device for further analysis.
The switches, if managed, might also support that.
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fred2k3Author Commented:
Thank you Qlemo - that makes sense.

If I was able to situate a system with 2 NICs in between the router and the LAN switch, is there anything I can run which would forward all packets through, whilst collecting metrics (perhaps using Netflow)?
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
Putting a router between LAN and router works, and what you suggested is nothing else than a router ;-). Netflow would not be required then, because you can collect all necessary info at the router.

You should be able to use a Windows machine for that, but it might be necessary to set a reg entry to switch on routing, and run the Routing and Remote Access service (if available). Then you can record with WireShark, and apply some analysis to the result.

But I would look first at the existing router, and whether it can give you some hints without adding effort. If your Internet bandwidth is not saturated, and the router CPU does not have issues, it is probably useless to monitor Internet traffic ...
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TjnoNetwork AdministratorCommented:
You can use Zabbix, it is free and easy to configure. Some screenshots here:

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fred2k3Author Commented:
Hah, yes that's a good point lol  

Appreciate  your advice, thank you.
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