help with tcpdump cmd syntax

Karol Kwiatkowski freebsd at
Sat Apr 8 13:19:55 UTC 2006

On 08/04/2006 14:56, fbsd_user wrote:
> I tried 
>    tcpdump -i rl0 src host -w /usr/
>    tcpdump -i rl0 host -w /usr/
>    tcpdump -i rl0 src ip -w /usr/  
> but got syntax error msg with no hint of what was wrong
> If I remove the -w stuff it works. Meaning it prints to the screen.
> But I want to write to file
> Can you help me out here on the syntax error?

Have a look at 'tcpdump -h' (or man, of course). Expression (i.e. 'src
host') is the last argument. This should work:

tcpdump -i rl0 -w /usr/ src host

> One other thing. When does tcpdump get access to the packet?
> My firewall has a block log rule for that ip address. 
> Does tcpdump see the packet before ipfilter ipnat does?

Yes. I'm not familiar with kernel code, but I can perfectly see all
packets with tcpdump.



Karol Kwiatkowski  <freebsd at orchid dot homeunix dot org>

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