[mrtg] MRTG

Steve Shipway s.shipway at auckland.ac.nz
Mon Aug 4 00:16:58 CEST 2008

To monitor how much traffic in total goes through an interface is easy with MRTG, provided the device supports SNMP.

However to monitor this split by source/destination IP address requires something called an RMAN probe, or similar.  Not may devices support this, and usually you need an extra device to do it.  This is because most routers/switches only count packets at the level below IP (I've forgotten my OSI model numbers...).  To count grouped by IP, they would need to do deeper packet inspection.  This is the same problem as when people ask to graph just the Web traffic on their network, which requires packet inspection down to the transport layer (TCP) to get the port number.

I've actually set up my home router to do exactly this, using the Linux firewall.  It counts internet traffic based on whose machine it is from/to, so I can hassle the appropriate teenager for using our data allocation...  This works because I have my wireless AP connected to the linux firewall, which then connects to the DSL, and the linux takes care of the NAT, DNS, DHCP, and firewall.  In your case it sounds as if your WRT54G is doing everything.  I also have a close relative of the WRT54G at my place, but I disabled the DNS,DHCP and DSL capabilities of it so as to use the Linux server for this instead (my DSL is not compatible with the WRT54G anyway)

In brief, I don't believe you can do what you want without additional more intelligent hardware, such as a linux firewall, or RMAN probe, or network sniffer.


From: mrtg-bounces at lists.oetiker.ch [mailto:mrtg-bounces at lists.oetiker.ch] On Behalf Of Al Grant
Sent: Sunday, 3 August 2008 10:04
To: mrtg at lists.oetiker.ch
Subject: [mrtg] MRTG

Hi Folks,

A bit of a newbie here.

Could someone please tell me if I can monitor how much traffic is being used monthly by a IP on the LAN using DD-WRT and MRTG?

Thanks in advance,

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