sniff cable modem

Hi, @user_689a3c, thank you for taking the time to reach out on our Xfinity Forums. Are you still in need of assistance regarding your connection set up? 

hi yes still needing help.

@user_689a3c Three suggestions-

1. I believe there are programs that run on desktop OS machines, such as Little Snitch for MacOS and ZoneAlarm for Windows. They won't see requests from other machines, however.

2. Another thing you could try is, buy a wifi+ethernet router that supports packet sniffing (aka the TAP protocol, I think?). You'd connect that router to the Comcast modem, disable wifi on the Comcast, plug one ethernet cable into the Comcast, the other end into your other/new router. All your traffic will pass through your new router. Now you'll need to use a program that can monitor the router.

Some brands of router support "mirroring traffic to a port" which means they'd copy all traffic, passing between the Comcast router and the wifi+ethernet router you added to it, to another machine on the network. That machine will need to run a program that knows how to process that traffic.

https://superuser.com/questions/503907/sniffing-and-logging-http-traffic-through-my-wireless-router

3. if you are feeling ambitious, putting two ethernet cards (aka NICs) into a purpose-built PC, and placing the PC between your Comcast modem and your own router, will provide the opportunity to analyse and filter traffic with the most flexibility. Your Comcast router may still accept wifi clients, which would bypass your two NIC PC. See if you can disable Wifi on the Comcast modem/router, if you want *all* traffic analysed & filtered. You'd then need your own router (which in this network arrangement you will anyways) which has wifi, for phones and tablets, and then that wifi traffic would be seen by your two NIC PC.

There are programs, such as snort (https://www.snort.org/), which provide ability to analyse and filter traffic passing through a two NIC PC.

There are Linux distros which have snort and other similar utilities baked-in, scroll down to 3rd Party Projects on snort's downloads page:

https://www.snort.org/downloads/#rule-downloads

Fair warning: you'll be entering system admin territory. If you've never run a Linux, don't know what a bash/csh/zsh is, I'd look for a Windows-based solution (or MacOS if that's your thing.)

See also- https://forums.xfinity.com/conversations/your-home-network/port-mirroring-on-xfinity-xfi-gateway/602db14ec5375f08cd4c6d27