Hi, for some reason Wireshark doesn't capture SIP messages even 
  when I'm leaving the filter empty.
It is also configured to capture packets 
  in promiscuous mode.
I am using 
SIPp (version 3.1.1) to generate the 
  SIP messages.
SIPp is a program that can generates SIP messages and check 
  that they are being received.
I'm running SIPp in two separate shells, 
  one that runs a default client scenario (uac) that generates INVITE 
  messages,
and in another shell a default server scenario (uas) that 
  receives the INVITE and confirms them with 200 OK responses.
Here is 
  the screenshoot of the client:
http://img231.imageshack.us/i/sippuac.jpg/Here 
  is the screenshoot of the server:
http://img207.imageshack.us/i/sippuas.jpg/As 
  you can see, the client sends INVITE messages and receives 200 OK responses 
  from the server,
and the server receives INVITE messages and sends 200 OK 
  to the client.
So the problem is not with the sending/receiving of the 
  messages but with wireshark.
Do you know what could be the problem and 
  how to fix it?
Thanks