Schedule fw monitor to run unattended /fw monitor command reference

Not a groundbreaking idea but worth remembering that you can also run scheduled fw monitor using the cron. In case you have some problem occurring at the late night hours or you want to run debug at night when system is loaded less or put your case here this is one of the ways to do it.
First, the script named timed_fw_monitor.sh that starts the fw monitor:

#!/bin/bash
# We have to source Checkpoint environment variables for fw monitor to work
. /etc/profile.d/CP.sh
/opt/CPsuite-R71/fw1/bin/fw monitor -o /home/lambada/capture.cap -e 'accept icmp or port(25);'

Then of course I will want to stop fw monitor , here is the script named stop_fw_monitor.sh that I also put in cron jobs that stops previously started fw monitor :

#!/bin/bash
ps ax | grep 'capture.cap' | grep -v grep | awk '{ print ("kill -s 3 " $1) | "/bin/bash" }'

Now my crontab looks like this:

# DO NOT EDIT THIS FILE – edit the master and reinstall.
# (/tmp/crontab.4760 installed on Sat May 29 11:00:22 2010)
# (Cron version — $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)
03 23 * * * /home/lambada/timed_fw_monitor.sh > /dev/null
17 23 * * * /home/lambada/stop_fw_monitor.sh > /dev/null

fw monitor command reference

This is a quick reference sheet of all usable options for the fw monitor tool .At the end I put a list of fw monitor examples. The previous experience with the tool is assumed, i’ll just say that if you are serious about debugging Checkpoint products learn it and learn it well.
By default the fw monitor sniffing driver is inserted into the 4 locations on
the Firewall kernel chain .

Here they are:

 i (PREIN) – inbound direction before firewall Virtual
Machine (VM, and it is CP terminology) . Most important fact to know about that
is that this packet capturing location shows packets BEFORE any security rule
in the policy is applied. That is, no matter what rules say a packet should at
least be seen here, this would prove that packets actually reach the firewall
at all.
 I (POSTIN) – inbound direction after firewall VM.
 o (PREOUT) – outbound direction before firewall VM,
 O (POSTOUT) – outbound direction after firewall VM.

You can change point of insertion within the fw chain with :

# fw monitor –p<i|I|O|o> <where to
insert>

easiest way to specify where to insert is to first see the chain:
# fw ctl chain 
then give relative to any module you see there <+|->module_name

Now the usage itself:

# fw monitor

Usage: fw monitor [- u|s] [-i] [-d] [-T] <{-e
expression}+|-f <filter-file|->> [-l len] [-m mask] [-x offset[,len]]
[-o <file>] <[-pi pos] [-pI pos] [-po pos] [-pO pos] | -p all [-a
]> [-ci count] [-co count]

Round up of options:

-m mask , which point of capture is to be displayed, possible: i,I,o,O
-d/-D debug output from fw monitor itself, not very useful IMO.
-u|s print also connection/session Universal ID
- i after writing each packet flush stdout
-T add timestamp, not interesting
-e expr expression to filter the packets (in detail later)
-f filter_file the same as above but read expression from file
-l <len> packet length to capture

Expressions 
On the very low level fw monitor understands byte offsets from the header
start. So to specify for example 20th byte of the IP packet (that is source IP)
you can just use:

# fw monitor -e 'accept [12,b]=8.8.8.8;'

Where:
12 – offset in bytes from the beginning of the packet
b – mandatory, means big endian order.
4 – not seen here but size (in bytes) of how many bytes to look for from the
starting offset (default is 4 )

To look for source port 53 (UDP/TCP) in raw packet:

# fw monitor -m i -e 'accept [20:2,b]=53;' 
Here I say to fw monitor to look at 2 bytes at offset 20.

While this way of looking at packets is the most general and therefore includes
all cases, you rarely have the need for such a granular looking glass. In 99%
of the cases you will be doing alright with a limited known set of expressions.
Just for that Checkpoint defined and kindly provided us in every Splat
installation with definition files that give meaningful synonyms to the most
used patterns. There are few definition files but they circularly reference
each other providing multiple synonyms for the same pattern.
I put all those predefined patterns in the list below for the easy to use
reference.

Summary table of possible expressions to be fed to the fw monitor
Specifying Hosts
host(IP_address)	to or from this host
src=IP_address	where source ip = IP_address
dst=IP_address	where destination ip = IP_address
net(network_address,netmask)	to or from this network
to_net(network_address,netmask)	to this network
from_net(network_address,netmask)	from this network
Specifying ports
port(port_number)	having this source or destination port
sport=port_number	having this source port
dport=port_number	having this destination port
tcpport(port_number)	having this source or destination port that is also TCP
udpport(port_number)	having this source or destination port that is also UDP
Specifying protocols
ip_p=<protocol_number_as_per_IANA>	this way you can specifiy any known protocol by its registered number in IANAFor detailed list of protocol numbers see www.iana.org/assignments/protocol-numbers
icmp	what it says , icmp protocol
tcp	TCP
udp	UDP
Protocol specific oprions
IP
ip_tos = <value>	TOS field of the IP packet
ip_len = <length_in_bytes>	Length of the IP packet in bytes
ip_src/ ip_dst = <IP_address>	Source or destination IP address of the packet
ip_p =<protocol_number_as_per_IANA>	See above
ICMP
echo_reply	ICMP reply packets
echo_req	Echo requests
ping	Echo requests and echo replies
icmp_error	ICMP error messages (Redirect,Unreachables,Time exceeded,Source quench,Parameter problem)
traceroute	Traceroute as implemented in Unix (UDP packets to high ports)
tracert	Traceroute as implemented in Windows (ICMP packets , TTL <30)
icmp_type = <ICMP types as per RFC>	catch packets of certain type
icmp_code = <ICMP type as per RFC>	catch packets of certain code
ICMP types and where applicable respective codes:ICMP_ECHOREPLY ICMP_UNREACH       ICMP_UNREACH_NET       ICMP_UNREACH_HOST       ICMP_UNREACH_PROTOCOL       ICMP_UNREACH_PORT       ICMP_UNREACH_NEEDFRAG       ICMP_UNREACH_SRCFAIL ICMP_SOURCEQUENCH ICMP_REDIRECT       ICMP_REDIRECT_NET       ICMP_REDIRECT_HOST       ICMP_REDIRECT_TOSNET       ICMP_REDIRECT_TOSHOST ICMP_ECHO ICMP_ROUTERADVERT ICMP_ROUTERSOLICIT ICMP_TIMXCEED       ICMP_TIMXCEED_INTRANS       ICMP_TIMXCEED_REASS ICMP_PARAMPROB ICMP_TSTAMP ICMP_TSTAMPREPLY ICMP_IREQ ICMP_IREQREPLY ICMP_MASKREQ ICMP_MASKREPLY
icmp_ip_len = <length>	Length of ICMP packet
icmp_ip_ttl = <TTL>	TTL of ICMP packet, use with icmp protocol otherwise will catch ANY packet with TTL given
< cut here—-bunch of other icmp-related fields like ID ,sequence I don’t see any value in bringing here–>
TCP
syn	SYN flag set
fin	FIN flag set
rst	RST flag set
ack	ACK flag set
first	first packet (means SYN is set but ACK is not)
not_first	not first packet (SYN is not set)
established	established connection (means ACK is set but SYN is not)
last	last packet in stream (ACK and FIN are set)
tcpdone	RST or FIN are set
th_flags – more general way to match the flags inside TCP packets
th_flags = TH_PUSH	Push flag set
th_flags = TH_URG	Urgent flag set
UDP
uh_ulen = <length_in_bytes>	Length of the UDP header (doesnt include IP header)

And the last thing to remember before we move to examples – expressions support logical operators and numerical values support relative operators:

and – logical AND
or – logical OR
not - logical NOT
> MORE than
< LESS than
>= MORE than or EQUAL to
<= LESS than or EQUAL to
You can combine logical expressions and influence order by using ()

Below is laundry list of examples to showcase the reference table above.

# fw monitor -m i -e 'accept host(208.44.108.136) ;'
# fw monitor -e 'accept src=216.12.145.20 ;'  packets where source ip = 216.12.145.20 
# fw monitor -e 'accept src=216.12.145.20 or dst= 216.12.145.20;'  packets where source or destination ip = 216.12.145.20
# fw monitor -e 'accept port(25) ;'  packets where destination or source port = 25
# fw monitor -e 'accept dport=80 ;'  packets where destination port = 80
#fw monitor -e 'accept sport>22 and dport>22 ; '  packets with source and destination ports greater than 22
# fw monitor -e 'accept ip_len = 1477;'  packets where their length equals exactly 1477 bytes
# fw monitor -e 'accept icmp_type=ICMP_UNREACH;'  ICMP packets of Unreachable type
# fw monitor -e 'accept from_net(216.163.137.68,24);'  packets having source IP in the network 216.163.137.0/24
# fw monitor -e 'accept from_net(216.163.137.68,24) and port(25) and dst=8.8.8.8 ;'  packets coming from network 216.163.137.0/24 that are destined to the host 8.8.8.8 and hving source or destination port = 25
# fw monitor -m i -x 40,450 -e 'accept port(80);'  incoming packets before any rules are applied also
display contents of the packet starting at 40th byte of 450 bytes length 
# fw monitor -m i -pi -ipopt_strip -e 'accept host(66.240.206.90);'  incoming packets from/to host 66.240.206.90 , insert sniffer before module named ipopt_strip 
# fw monitor -D -m i -pi -ipopt_strip -e 'accept host(66.240.206.90);'  same as above but add debug info