[Bro] is_tcp_port

Christian Kreibich christian at whoop.org
Wed Aug 3 13:41:26 PDT 2005

On Wed, 2005-08-03 at 14:34 -0500, Mike Muratet wrote:
> Hello Again
> I was trying to figure out the tcp/udp flag in conn.bro:record_connection 
> from is_tcp_port and I got as far as bro.bif before I got lost.

The functions listed in .bif files are Built-In Functions, i.e.,
functions implemented in the core. To find such a function's
implementation, go to the src directory, and find the corresponding .bif
file, in this case bro.bif, which shows:

function is_tcp_port%(p: portval%): bool
	return new Val(p->IsTCP(), TYPE_BOOL);

Next you need to know that a portval in the policy is mapped to a
PortVal object in the core, so the implementation of PortVal::IsTCP() is
found in Val.cc.

> I was 
> looking at the iana.org site and it looks like it's a pretty degenerate 
> test, i.e., all the ports can be either.

Yeah sure, both UDP and TCP can have ports 0-65535.

> How does bro determine tcp vs udp?

>From looking at the IP header of the sniffed packets, which tell Bro
what protocol is at the transport layer. Check NetSessions::DoNextPacket
around line 436 and Stevens' TCP/IP Illustrated Vol 1 for details.


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