From mboxrd@z Thu Jan 1 00:00:00 1970 From: chuck gelm Subject: Re: tcpdump: How do I filter 'bootp' packets? Date: Wed, 08 Dec 2004 17:56:22 -0500 Message-ID: <41B78696.7000500@gelm.net> References: <5.1.0.14.1.20041207220544.01f98370@celine> <41B6FDFC.3070309@gelm.net> <41B77BE5.6000001@verizon.net> Reply-To: chuck@gelm.net Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <41B77BE5.6000001@verizon.net> Sender: linux-newbie-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Jim Nelson Cc: linux-newbie@vger.kernel.org Jim Nelson wrote: > chuck gelm wrote: > >> Howdy: >> >> I have cable modem access to the internet now and the download speed is >> double my original DSL speed. :-) However, I am concerned about >> security. >> >> Can other cable modem subscribers see my packets? >> > > IIRC, most modern cable modems filter anything not addressed to them - > you'd have to hack your modem to get it to go into promiscuous mode. > > It's not easy to do, and it relies on brain-dead network admins to leave > some back doors in. > > OTOH, you could probably find hardware to do just this - if you were in > law enforcement. > >> To test this, I am trying to use tcpdump to monitor packets that my >> cable modem is sending to my 'router'. >> >> I am using these arguments: >> tcpdump -i eth1 -c 9 -nt not arp and not host W.X.Y.Z > \ >> http://gelm.net/tcpdump.txt >> >> >> ( == My assigned IP address) >> >> I am still seeing many 'bootp' packets. >> >> How do filter out 'bootp' packets with tcpdump? >> >> Regards, Chuck Hi, Jim: I am filtering 'my ip', port 67, and 'arp' and, for several minutes now, tcpdump has displayed zero packets. So, I seems that... It would require special hardware for others to view my packets. I wanted to be sure that it wouldn't be easy. Regards, Chuck - To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs