I would like to monitor the traffic between my router/modem and my ISP. However, I am led to believe that traffic other than what is meant for my network may be sent and thrown away by my router/modem. Is this true? If so I can appreciate the security implications and thus not enable the ISP / router/modem monitoring. If this is not true then is it possible to monitor this traffic? If so how can this be accomplished?
thanks,
ian t.

depending on your ISP, the WAN side of your router/modem may be constantly bombarded by ARP packets from their head-end, as well as occasional DHCP messages. it's all normal traffic, necessary for operation of the ISPs network. it would be possible to monitor this traffic if you have the requisite tools available on the router; though i'm not sure how interesting the results would be. and no, you typically cannot see other subscribers traffic.

Thank you psycroptic.
"Tools on the router." Can you give the name of these tools?
cheers
ian t.

sure; tcpdump, and its many associated front-ends (wireshark, tshark, etc.) is a packet trace utility. ran on the WAN interface of the router, it prints out info/payload for every packet that hits it.

i will say, if you do not have command-line access to the router, then it will be virtually impossible to run this (or any other utility) from its GUI config screens. though custom firmwares may. if this is one of those "combo" units rented out by ISPs, then you're hosed.

Thanks for your info. I use wireshark on my NIC but it only shows the traffic on the local side, even with promiscuous mode set. I was hoping to see the other side of the modem/router.
ian t.

right, you would have to run wireshark ON the router directly, not on your machine.

Depending on your system, you may or may not easily be able to actually monitor the wan. In some cases you can put your modem in bridged mode and authenticate via the computer.
In some cases you can nat the wan or dmz it to a computer.

But, yes, in most tcp/ip type situations where there is an IP address at the modem, there is also (could be) a lot of traffic. It may depend also on how your isp has devices configured and who is out trying to access your network. Millions of crooks have automated systems trying to attack any ip out there.