Capturing packets from my WAN/Router

{O_o} · 10-11-2005, 04:26 PM

hello,

I like to use tcpdump to monitor incoming packets, however i just got a new router for adsl and rather than listening to whats coming in to me i want to listen to whats happening on the routers WAN. I can access the firewall logs, but they are not very verbose (and i like verbosity). My router is ip 10.0.0.x as is my desktop, is it possible to use the router as an interface rather than just forwarding everything to me?

Brian1 · 10-11-2005, 09:07 PM

Not to my knowledge. The router is setup to block incoming traffic, unless up portforward. Some routers can actually setup something called a DMZ, but I do not know if that transmit the network packets to that IP you define. You need to connect your computer directly to the adsl modem to get that info.

Brian1

Slim_Pikins · 10-12-2005, 09:08 AM

hi

what I do is use transparent bridging (sometimes called half bridging) even most of the cheapest adsl routers usually have this option what make is yours?
What it does is pass the wan ip to your pc (kind of like forwarding all ports) and then you can run tcpdump to see whats happening on the wan side.

Dont forget this effectively disables the router firewall so get one on the pc first

Slim Pikins

slacky · 10-12-2005, 01:35 PM

Linux can do bridging too (http://bridge.sourceforge.net/) - what you could do, if you have an extra pc, you can put two NICs in it, bridge them without assigning an ip address, connect your WAN to one, then your router to the other, and run tcpdump (or snort or whatever) on the Linux bridge and monitor away. I also suppose if you put two extra NICs in your main PC you could use them as a bridge as well.

{O_o} · 10-12-2005, 04:56 PM

Brian1: My router does indeed have a DMZ zone setting, though i don't actually know what this means (im still new to the whole networking thing) ill go google it.

Slim_Pikins: It also has a virtual bridge section which i have used in the past for port forwarding, but i dont like this. As you said it disables the firewall, and i like having the routers firewall to control incoming connections and my os firewall to control outgoing it makes me feel () safe

slacky: Your suggestion sounds both like the best solution (and also sounds like it would be fun) i have a spareish laptop i can try that with?

Thanks again for the info, most helpfull.