How to sniff packets from router

What is the best way to look at real time traffic on you r router?? Can this be done with Linux/Unix? IS there some kind of command line tool to do this.

Thanks


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andrew_89Asked:
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grsteedCommented:
"Also how would you re-route traffic say for ftp"

You don't mention what kind of routers you have but if they are Cisco you may be able to use Policy Based Routing to do this. (other routers support this as well) It still depends on your topology.

Basically Policy Based Routing uses access lists and route-maps to make routing decisions. If you use Extended access lists, the decision could be based on TCP ports, along with Source and Destination. It doesn't control the destination of a packet, but can control the path it takes.  

Here's a few links if you want to read more.

http://www.21stcenturyarticles.com/Article/Cisco-CCNP---BSCI-Exam-Tutorial---Introduction-To-Policy-Routing/580
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfindep.htm#wp1001398
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt1/qcfpbr.htm

 
Cheers,

Gary

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andrew_89Author Commented:
Also how would you re-route traffic say for ftp to your secondary router to alleviate bandwidth consumption on the primary router?
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Tony GimenezInternshipCommented:
http://www.ethereal.com

Its for Windows and Linux and its free!
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Tony GimenezInternshipCommented:
If you need other programs for similar uses this should help
http://www.google.com/search?hl=en&lr=&q=real+time+network+monitoring&btnG=Search

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giltjrCommented:
What is the router connected to?  If it is a switch, then you need to have a managed switch that you can mirror the port that the router is connected to, that is you tell the switch to send a copy of all data that is going to or coming from port "A" to port "B"  Then you connect a computer to port "B" that has packet caputer software (like Ethereal).

That I am aware of I don't know of away to route traffic based on the application (ftp, http, telnet).  Routing is based on destination IP address.  Do you want to route all FTP traffic, or say ftp traffic from a specic host?  You should just change that hosts  default route.  Or, you could setup a ftp proxy server and have its default route be your "secondary" router.

However, in order for this to work, not only would you need a secondary router, you would need a secondary connection to the Internet.  Wouldn't it be less expensive to just increase the bandwidth on the primary connection?
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ragnarok89Commented:
You can monitor the amount of traffic going through a switch using Getif or a similar program that uses SNMP. This program can tell you (for example) the number of packets sent or received on a particular interface.

In order to see inside each packet, you will need a packet analyser such as ethereal, which can examine the headers and data inside each packet.

In order to route traffic, you will need a router with which you can create a port forwarding rule. So any traffic received for port 22 (ftp) would be directed to a specific IP address on your internal network - like your ftp server.
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DazmCommented:

Try this easy to use program
"Ether Detect Packet Sniffer"
http://www.etherdetect.com

Maybe not the best, But truly the best : )
Is so easy that i don't have to tell you nothing else here.

Try it and let me know.
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Psyco_666Commented:
If you dont have a managed switch you could replace the cable from your router to your internal network with 2 cables and a 4 port hub in between. This way you can plug in an ethereal laptop in any time to check on traffic loads. Only really works if you have a one in one out setup.

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