[Click] Accessing port values from header

[Michael Gellman]

On Thu, 2006-04-06 at 18:03 +0100, Daniel Braund wrote:
> Hi. I am running in circles trying to figure out how to extract the port value 
> for a packet in a similar manner to the way I extract a packets source and 
> destination addresses:
> 
> packet_src=iph->ip_src.s_addr;
> packet_dst=iph->ip_dst.s_addr;
> 
> essentially I want to know if I can do something like
> 
> packet_port=iph->ip_dst.port;
> 

IP Headers don't have ports -- but TCP and UDP headers do. For UDP, you
would access the ports of a Packet p using:

  p->udp_header()->uh_sport
  p->udp_header()->uh_dport

assuming the transport header has been set in the packet.

> I have looked, but cannot find a list or description of what values I can plug 
> into here to gain the data I want. Does one exist somewhere? Also, s_addr I 
> assume implies string, is there a binary/hex variant?

s_addr is a 32-bit integer. It is the only member of the in_addr struct
which is defined in <linux/in.h> under Linux.

Michael Gellman
-- 
Intelligent Systems & Networks Group
Dept of Electrical & Electronic Engineering
Imperial College London
London SW7 2BT