dumping net traffic to log file

[Steel City Phantom]

   im trying the command
   tcpdump -i em0 > traffic.log
   and i get the response
   tcpdump: (no devices found) /dev/bpf0: No such file or directory
   im doing it as root.  this is a dell poweredge 2850 and we are using
   the standard gigabit network cards that came onboard.  here are the
   details on the nic
   em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
           options=b<RXCSUM,TXCSUM,VLAN_MTU>
           inet 192.168.245.246 netmask 0xffffff00 broadcast
   192.168.245.255
           ether 00:13:72:56:aa:ca
           media: Ethernet autoselect (100baseTX <half-duplex>)
           status: active
   in my dev directory em0 is mapped to net1.  when i try the same
   command with net1, i get the same thing.
   Darrin Chandler wrote:

On Mon, Jul 24, 2006 at 03:20:32PM -0400, Steel City Phantom wrote:
  

i am troubleshooting an application and am having a hell of a time with 
it.  with bsd 6.1 is there a way where i can dump all traffic coming 
over the nic to a log file so i can see exactly what is coming in?
    

tcpdump works nicely for this. :)