Re: tcpdump: How do I filter 'bootp' packets?

[chuck gelm <chuck@gelm.net>]

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
>>
>>
>>  (<W.X.Y.Z> == 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


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