Table of Contents:

• Introduction
• Warnings
• FW Monitor Features
• FW Monitor Functionality
• FW Monitor Documentation
• FW Monitor Syntax
• SecureClient Syntax
• Examples
  • Usual Capture
  • Port Specific Capture
  • Protocol Specific Capture
  • Bytes Specific Capture
  • Network Specific Capture
  • Examples
• Related solutions

Introduction

Check Point's 'FW Monitor' is a powerful built-in tool for capturing network traffic at the packet level. The 'FW Monitor' utility captures network packets at multiple capture points along the FireWall inspection chains. These captured packets can be inspected later using the WireShark (available for free from www.wireshark.org).

Warnings

• Anything related to policy installation or policy unloading on Security Gateway, will cause 'FW Monitor' to exit.
  
  
• It is supported to run only a single instance of 'FW Monitor' at any given time.
  
  
• Do not modify Check Point kernel tables used in the security policy while 'FW Monitor' is running, otherwise unexpected behavior may result (including a system crash).
  
  
• Packets are defragmented as they leave the Security Gateway in both the inbound and outbound directions.
  
  
• If SecureXL is enabled on the Security Gateway, then 'FW Monitor' and 'tcpdump' will show only the non-accelerated packets (e.g., 'TCP SYN' will be shown, and 'TCP ACK' will not).
  
  
• * NOTE * - Traffic captures can be misleading when working with SecureXL since both FW Monitor and TCPdump do not always show 'real' packets that are going out to the network. This is related to the way the SecureXL kernel driver is attached to the network adapter itself. When using SecureXL to confirm whether packets are being handled correctly, either capture the traffic on the directly connected router / switch, or disable SecureXL.

FW Monitor Features

In many deployment and support scenarios, capturing network packets is an essential functionality. The 'tcpdump' / 'snoop' utilities are normally used for this task. The 'FW Monitor' utility provides an even better functionality, but omits many of the requirements and the risks associated with these tools:

• No Security Flaws
  
  'tcpdump' / 'snoop' are normally used with NICs in promiscuous mode. Unfortunately, promiscuous mode allows remote attacks against these tools. Check Point's 'FW Monitor' does not use promiscuous mode to capture packets. In addition, most firewalls' operating systems are hardened. In most cases, this hardening includes the removal of tools like 'tcpdump' / 'snoop', because of their security risks.
  
  
• Available on FireWall Installations
  
  'FW Monitor' is a built-in tool that does not need a separate installation, or licensing.
  
  
• Multiple Capture Positions within the FireWall Kernel Module Chains
  
  'FW Monitor' allows to capture packets at multiple capture positions within the Security Gateway kernel module chains, both for inbound and outbound packets. This enables to trace a packet through the different layers of the Security Gateway.
  
  
• Same Tool and Syntax on All Platforms
  
  'FW Monitor' is available on all different platforms. 'tcpdump' / 'snoop' are often platform-dependent, or have specific "enhancements" on certain platforms. 'FW Monitor' and all its related functionality and syntax are identical across all platforms.

Normally, Check Point kernel modules are used to perform several functions on packets, such as filtering, encryption and decryption, QoS, etc. 'FW Monitor' adds its own modules to capture packets. 'FW Monitor' can capture all packets that are seen and/or forwarded by the Security Gateway.

FW Monitor Functionality

There are four inspection points when a packet passes through a Security Gateway:

1. Before the FireWall Virtual Machine, in the inbound direction - Pre-Inbound - marked as 'i'
   
   
2. After the FireWall Virtual Machine, in the inbound direction - Post-Inbound - marked as 'I'
   
   
3. Before the FireWall Virtual Machine, in the outbound direction - Pre-Outbound - marked as 'o'
   
   
4. After the FireWall Virtual Machine, in the outbound direction - Post-Outbound - marked as 'O'

Note:
The direction (inbound/outbound) relates to each specific packet, and not to the connection.

Let us examine a TCP handshake in the following topology:
[Source/Client] --- (eth1)[Security Gateway](eth2) --- [Destination/Server]

• TCP SYN from [Source/Client] will pass through Pre-Inbound and Post-Inbound on interface eth1
• TCP SYN from [Source/Client] will pass through Pre-Outbound and Post-Outbound on interface eth2
• TCP SYN-ACK from [Destination/Server] will pass through Pre-Inbound and Post-Inbound on interface eth2
• TCP SYN-ACK from [Destination/Server] will pass through Pre-Outbound and Post-Outbound on interface eth1
• TCP ACK from [Source/Client] will pass through Pre-Inbound and Post-Inbound on interface eth1
• TCP ACK from [Source/Client] will pass through Pre-Outbound and Post-Outbound on interface eth2

Once started, the 'FW Monitor' compiles the INSPECT filter (created as $FWDIR/tmp/monitorfilter.pf) based on the specified syntax (which packets to capture), and loads it to the Check Point kernel (not replacing the Security Policy). The 'FW Monitor' will then continuously get packets from the Check Point kernel, and depending on the syntax, will either display them on the terminal window , or will save them in the output capture file. Upon an interrupt signal (key combination CTRL + C), the 'FW Monitor' stops, unloads the INSPECT filter, and exits.

FW Monitor Documentation

Detailed information regarding the usage of the 'fw monitor' command can be found in the "How to use FW Monitor" document.
This document applies to Security Gateways of all existing Check Point versions, regardless of operating system.

Note: please ignore the links provided in the document in the "Secure Knowledge Links" section.

FW Monitor Syntax

[HostName]# fw monitor [-h] [-u|-s] [-i] [-d] [-D] [-t] [{-e <expr>}+ | -f <filter_file_name>|-] [-l length] [-m i|I|o|O] [-x offset[,length]] [-o <output_file_name>] <[-pi position] [-pI position] [-po position] [-pO position] | -p all> [-a] [-ci count] [-co count] [-vs VSID]

SecureClient Syntax

• SecurRemote and SecureClient R56 / R60 uses an abridged version of 'FW Monitor' - called 'srfw monitor':

  %SRDIR%\bin\srfw monitor [-d] [{-e <expr>}+ | -f <filter_file_name> |-] [-l length] [-m i|I|o|O] [-x offset[,length]] [-o <output_file_name>]

  Refer to SecureClient R56 for Mac OS X Release Notes (Mac OS X 10.3, Mac OS X 10.4) and to Debugging SecuRemote/SecureClient.

• Starting in E75.30, SecurRemote and SecureClient uses command line packet monitoring utility (PacketMon.exe) - called 'packetmon':

  packetmon [-d] [-h] [-t] [-T] [-i] [-I] [-r] [{-e <expr>}+ | -f <filter_file_name> | -] [-l length] [-m i|I|o|O] [-x offset[,length]] [-o <output_file_name>] [-ci count] [-co count]

  Refer to Remote Access Clients for Windows 32/64-bit Administration Guide (E75.30, E80.41, E80.50) - Chapter 'Monitoring and Troubleshooting' - Troubleshooting the Firewall - Desktop Firewall Monitoring.

Examples

Refer to $FWDIR/lib/fwmonitor.def file for useful macro definitions.

Refer to "How to use FW Monitor" document - 'Logical and Relational Operators' section.

Usual Capture

Capture everything, save the data into the file:
[Expert@HostName]# fw monitor -e "accept;" -o /var/log/fw_mon.cap

Capture everything between host X and host Y:
[Expert@HostName]# fw monitor -e "((src=x.x.x.x , dst=y.y.y.y) or (src=y.y.y.y , dst=x.x.x.x)), accept;" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "host(x.x.x.x) and host(y.y.y.y), accept;" -o /var/log/fw_mon.cap

Capture everything between hosts X,Z and hosts Y,Z on all Check Point kernel chains:
[Expert@HostName]# fw monitor -p all -e "((src=x.x.x.x or dst=z.z.z.z) and (src=y.y.y.y or dst=z.z.z.z)), accept ;" -o /var/log/fw_mon.cap

Capture everything to/from host X or to/from host Y or to/from host Z:
[Expert@HostName]# fw monitor -e "((accept (src=x.x.x.x or dst=x.x.x.x)) or (accept (src=y.y.y.y or dst=y.y.y.y)) or (accept (src=z.z.z.z or dst=z.z.z.z)));" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "host(x.x.x.x) or host(=y.y.y.y) or host(=z.z.z.z), accept;" -o /var/log/fw_mon.cap

Port Specific Capture

Capture everything to/from port X:
[Expert@HostName]# fw monitor -e "accept (sport=x or dport=x);" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "port(x), accept;" -o /var/log/fw_mon.cap

Capture everything except port X:
[Expert@HostName]# fw monitor -e "accept not (sport=x or dport=x);" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "((sport=!x) or (dport=!x)), accept;" -o /var/log/fw_mon.cap

Capture everything except SSH:
[Expert@HostName]# fw monitor -e "accept not (sport=22 or dport=22);" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "((sport!=22) or (dport!=22)), accept;" -o /var/log/fw_mon.cap

Capture everything to/from host X except SSH:
[Expert@HostName]# fw monitor -e "((accept (src=x.x.x.x or dst=x.x.x.x)) and (accept not (sport=22 or dport=22)));" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "((host(x.x.x.x) and (sport!=22 or dport!=22)), accept;" -o /var/log/fw_mon.cap

Protocol Specific Capture

Note: Protocol number in the syntax has to be provided in Decimal format. Refer to '/etc/protocols' file on the machine, or to 'www.iana.org/assignments/protocol-numbers/'

Capture everything on protocol X:
[Expert@HostName]# fw monitor -e "ip_p=X, accept;" -o /var/log/fw_mon.cap

Everything on protocol X and port Z on protocol Y:
[Expert@HostName]# fw monitor -e "(ip_p=X) or (ip_p=Y, port(Z)), accept;" -o /var/log/fw_mon.cap

Capture everything TCP between host X and host Y:
[Expert@HostName]# fw monitor -e "ip_p=6, host(x.x.x.x) or host(=y.y.y.y), accept;" -o /var/log/fw_mon.cap
[Expert@HostName]# fw monitor -e "accept [9:1]=9 , ((src=x.x.x.x , dst=y.y.y.y) or (src=y.y.y.y , dst=x.x.x.x));"
[Expert@HostName]# fw monitor -e "ip_p=6, ((src=x.x.x.x , dst=y.y.y.y) or (src=y.y.y.y , dst=x.x.x.x)), accept;" -o /var/log/fw_mon.cap

Bytes Specific Capture

Simple checks are used to check for a value at a specific offset in the packet:

[Expert@HostName]# fw monitor -e "accept [ offset : length , order ] relational-operator value;"

The IP-based protocols are stored in the IP packet as a byte at offset 9:

• To filter based on a Protocol encapsulated into IP, use "accept [9:1]=Protocol_Number_in_Decimal_format;" syntax

The Layer 3 IP Addresses are stored in the IP packet as double words at offset 12 (Source address) and at offset 16 (Destination address):

• To filter based on a Source IP address, use "accept [12:4,b]=IP_Address_in_Doted_Decimal_format;" syntax
• To filter based on a Destination IP address, use "accept [16:4,b]=IP_Address_in_Doted_Decimal_format;" syntax

The Layer 4 Ports are stored in the IP packet as a word at offset 20 (Source port) and at offset 22 (Destination port):

• To filter based on a Source port, use "accept [20:2,b]=Port_Number_in_Decimal_format;" syntax
• To filter based on a Destination port, use "accept [22:2,b]=Port_Number_in_Decimal_format;" syntax

Capture everything between host X and host Y:
[Expert@HostName]# fw monitor -e "accept (([12:4,b]=x.x.x.x , [16:4,b]=y.y.y.y) or ([12:4,b]=y.y.y.y , [16:4,b]=x.x.x.x));" Capture everything on port X:
[Expert@HostName]# fw monitor -e "accept [20:2,b]=x or [22:2,b]=x;" -o /var/log/fw_mon.cap

Network Specific Capture

Capture everything on network 192.168.33.0/24:
[Expert@HostName]# fw monitor -e "net={<192.168.33.0,192.168.33.255>}; dst in net, accept;"

Examples

Capture ESP protocol or UDP port 161 (SNMP):
[Expert@HostName]# fw monitor -e "(ip_p=50) or (ip_p=17, port(161)), accept;" -o /var/log/fw_mon.cap > /dev/null 2>&1 &

Filter out the usual garbage (SMTP, POP3, SSH, Microsoft NetBIOS, Check Point ClusterXL CCP):
[Expert@HostName]# fw monitor -e "(sport!=25) and (dport!=25) and (sport!=110) and (dport!=110) and (sport!=22) and (dport!=22) and (sport!=137) and (dport!=137) and (sport!=8116) and (dport!=8116), accept;" -o /var/log/fw_mon.cap > /dev/null 2>&1 &

Filter out the usual garbage (filter in only TCP protocol, and HTTP and HTTPS ports ; filter out the SSH and FW Logs):
[Expert@HostName]# fw monitor -e "accept (ip_p=6) and (not (sport=22 or dport=22)) and (not (sport=257 or dport=257)) and ((dport=80 or dport=443) or (sport=80 or sport=443);" -o /var/log/fw_mon.cap > /dev/null 2>&1 &

Capture Edge communication on UDP ports 9281, 9282, 9283:
[Expert@HostName]# fw monitor -e "ip_p=17, (host(10.10.10.10) or host(20.20.20.20) or host(30.30.30.30)) and (port(9281) or port(9282) or port(9283)), accept;" -o /var/log/fw_mon.cap

Related solutions

• sk39510 (How to configure Wireshark for analysis of FW Monitor captures)
• sk41104 (What happened to Check Point Ethereal (CPEthereal)?)
• sk38602 (Interface is shown as 'UNKNOWN' in the FW Monitor output on IPSO OS)
• sk44358 ('Table offset out of range (6400)' error when starting FW Monitor)