This article guides you through setting up the Wireshark packet analyser to interpret captures as a Checkpoint FW-1 capture. This will only have an effect on captures taken using “fw monitor”, all other captures will read as normal.

1. Edit -> Preferences -> Protocols -> Ethernet -> Check “Attempt to interpret as Firewall-1 monitor file”:

 

2. Edit -> Preferences -> User Interface -> Columns -> click “New” to add a new column – give it a title of FW Monitor and choose FW-1 monitor if/direction as the format:

You should now have an extra column when you open a capture file – if you open an fw monitor capture file you will see  4 entries for each packet tracked as they go in one interface and out of another.

The ethernet interfaces e.g. eth0, eth1 etc etc are marked with either i, I, o or O.

i = pre-incoming ……….. I = post-incoming

o = pre-outgoing ……….. O = post outgoing

So ..

1          i    eth0                                  <- pre-IN: this is the packet as it arrives at the interface

2               eth0    I                            <- post-IN: this is the packet leaving the interface, now in the CheckPoint kernel

3         o    eth1                                  <- pre-OUT: this is the packet having left the kernel and arriving at the egress interface

4                eth1    O                           <- post-OUT: this is the packet leaving the interface

This is dead handy for loads of troubleshooting situations, an ovious one is NAT being applied, e.g.:

A packet from internal IP 10.1.1.1 headed for a destination on the internet 4.2.2.1 through a firewall with an external IP of 81.82.83.84 would look something like:

SRC                   DST                       FW1

10.1.1.1                4.2.2.1                i   eth0

10.1.1.1                4.2.2.1                eth0    I

10.1.1.1                4.2.2.1                o   eth1

81.82.83.84       4.2.2.1                eth1    O          <- NAT has been applied and the source IP is now the firewall’s external IP