At 08:13 AM 12/8/2004 -0500, 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?

 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



(<W.X.Y.Z> == My assigned IP address)

 I am still seeing many 'bootp' packets.

How do filter out 'bootp' packets with tcpdump?

Since bootp packets necessarily preceed assignment of an IP address, they are commonly broadcast (255.255.255.255) packets, removing the option of filtering by address. But they do come from standaard ports -- 67 for the server, 68 for the client -- so you can try filtering on port number.


Information connecting port numbers to service labels can be found in /etc/services (for the common ones), for future reference.







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