Help answer threads with 0 replies.
Go Back > Forums > Linux Forums > Linux - Security
User Name
Linux - Security This forum is for all security related questions.
Questions, tips, system compromises, firewalls, etc. are all included here.


  Search this Thread
Old 10-11-2005, 05:26 PM   #1
Registered: Mar 2004
Distribution: Slackware 14
Posts: 70

Rep: Reputation: 16
Capturing packets from my WAN/Router


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?
Old 10-11-2005, 10:07 PM   #2
LQ Guru
Registered: Jan 2003
Location: Seymour, Indiana
Distribution: Distribution: RHEL 5 with Pieces of this and that. Kernel, KDE 3.5.8 and KDE 4.0 beta, Plu
Posts: 5,700

Rep: Reputation: 62
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.

Old 10-12-2005, 10:08 AM   #3
LQ Newbie
Registered: Jul 2004
Location: Manchester UK
Posts: 21

Rep: Reputation: 15

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
Old 10-12-2005, 02:35 PM   #4
Registered: Feb 2004
Location: USA
Distribution: Debian
Posts: 174

Rep: Reputation: 16
Linux can do bridging too ( - 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.
Old 10-12-2005, 05:56 PM   #5
Registered: Mar 2004
Distribution: Slackware 14
Posts: 70

Original Poster
Rep: Reputation: 16
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.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Find WAN ip from behind router Rizla Linux - Networking 7 05-27-2005 05:19 AM
VoIP Packets capturing in linux fastian Linux - Networking 1 03-25-2005 12:34 PM
capturing ethernet packets shrike_912 Programming 5 08-02-2004 02:46 PM
Linux router WAN Issue trees Linux - Networking 2 04-13-2004 03:20 PM
Capturing packets in ethereal as non-root user? maxor Linux - Software 6 08-27-2003 04:05 PM > Forums > Linux Forums > Linux - Security

All times are GMT -5. The time now is 05:23 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration