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I have a Cisco DPC3825 DOCSIS 3.0 modem/router combo. I want to monitor the traffic that passes through my router such as bandwidth usage.

I have bandwidth meters like DuMeter on my PC to monitor traffic that goes through the PC. But I have other devices like my PS3 or mobile devices that connect wirelessly and I want to monitor that traffic as well. So I can have a more accurate log of bandwidth usage.

I need some sort of router software to do so. The only way I can do so is by installing some custom firmware for the router. Now I don't think there's any custom firmware for this specific device and the fact that it's both a modem and router makes it troublesome to install custom firmware.

My motherboard actually has two ethernet ports. I read a method where one can mirror all packets going through the router and forward it all to a spare ethernet port on the router. I'm thinking of connecting port 4 to the spare ethernet port and having packets mirrored to port 4. Does anyone have any more information on this method?

Alternatively I'm also looking into a separate router that either has such a feature or is moddable to install custom firmware to do what I'm looking for. I'd like one that's relatively cheap < 100 and can support 50+ Mbps throughput.

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the router might be featuring a web interface or something like that...see the documentation of router to see the support it offers.. –  Vineet Menon Feb 9 '12 at 7:04

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up vote 5 down vote accepted

The normal way to do this is using an SNMP monitor.

Typical tools include MRTG enter image description here

Since the Cisco DPC3825 either doesn't support SNMP or has it disabled you may need to use a different router.

Someone with similar needs wrote

Another, and perhaps more functional way to get what you want would be to put the DPC3825 into bridge mode, and add an outboard Linksys router capable of running the "Tomato" third-party firmware. The Tomato firmware will provide you with the type of usage information you need.

At this point, I own a number of the Linksys WRT54G/L type routers which can be used for this.

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the linksys WRT54G is an amazing router for the price, Tomato or DD-WRT should both work for this. I have a couple of them myself. –  Rob Feb 9 '12 at 13:39
    
Do you know anything about the packet mirroring method to duplicate all packets and send it to a computer of my choosing to analyze? I had an old WRT54G from 2009 but it seems to bottleneck my speeds to ~30Mbps. –  Jack Feb 11 '12 at 5:31
    
@Jack, some Ethernet switches (particularly the more expensive "managed" switches) support port-mirroring especially for the purpose of packet montoring of all traffic on a LAN segment. However if your DSL router doesn't support SNMP it is unlikely to support port-mirroring on it's built-in Ethernet switch. SNMP is the best way to get overall statistics about bytes/sec in and out of your LAN. –  RedGrittyBrick Feb 11 '12 at 11:57

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