How to See a Network Flow Through the CLI in a Checkpoint Firewall
Notice: This blog post was originally published on Indeni before its acquisition by BlueCat.
The content reflects the expertise and perspectives of the Indeni team at the time of writing. While some references may be outdated, the insights remain valuable. For the latest updates and solutions, explore the rest of our blog
If you want to check the traffic flowing through a Checkpoint firewall without using the SmartView Tracker, you can use “fw monitor” command.
I will show you how to use fw monitor the way I use it for my troubleshooting process.
Take into consideration the following:
1. If you have a cluster, this command will show traffic flowing through the active firewall.
a. To check active status issue: cphaprob state
2. If you have SecureXL enabled, some commands may not show everything.
a. To disable SecureXL: fwaccel off
b. To enable SecureXL: fwaccel on
Traffic to/from a Host
You can check the traffic that a host is receiving or sending with the following command:
fw monitor -e “accept host(x.x.x.x);”
Example
CP-Firewall> fw monitor -e "accept host(192.168.1.86);" Compiled OK. monitor: loading monitor: monitoring (control-C to stop) [vs_0][fw_6] eth3:i[71]: 173.16.25.44 -> 192.168.1.86 (TCP) len=71 id=0 TCP: 43637 -> 443 F..PA. seq=4a5c5909 ack=df3170c0 [vs_0][fw_6] eth3:I[71]: 173.16.25.44 -> 192.168.1.86 (TCP) len=71 id=0 TCP: 43637 -> 443 F..PA. seq=4a5c5909 ack=df3170c0 [vs_0][fw_6] eth1:o[41]: 173.16.25.44 -> 192.168.1.86 (TCP) len=41 id=0 TCP: 43637 -> 443 F...A. seq=4a5c5927 ack=df3170c0 [vs_0][fw_6] eth1:O[41]: 173.16.25.44 -> 192.168.1.86 (TCP) len=41 id=0 TCP: 43637 -> 443 F...A. seq=4a5c5927 ack=df3170c0 monitor: caught sig 2 monitor: unloading CP-Firewall>
In this example, you can see the ingress interface (eth3) and the egress interface (eth1). Also, you can see the 4 capture points (iIoO):
| pre-inbound | i (lowercase i) |
|---|---|
| post-inbound | I (uppercase i) |
| pre-outbound | o (lowercase o) |
| post-outbound | O (uppercase o) |
You can also use set the capture points:
CP-Firewall> fw monitor -e "accept host(192.168.1.86);" -m iO Compiled OK. monitor: loading monitor: monitoring (control-C to stop) [vs_0][fw_6] eth3:i[64]: 173.16.25.44 -> 192.168.1.86 (TCP) len=64 id=0 TCP: 3932 -> 443 .S.... seq=ccbcc90f ack=00000000 [vs_0][fw_6] eth1:O[64]: 173.16.25.44 -> 192.168.1.86 (TCP) len=64 id=0 TCP: 3932 -> 443 .S.... seq=ccbcc90f ack=00000000
Traffic to/from a Network
You can check the traffic to a network with the following command. You can use 32 as netmask and would work like a host as well.
fw monitor -e "accept net(x.x.x.x,yy); "
Example (network 192.168.1.64/26)
CP-Firewall> fw monitor -e "accept net(192.168.1.64,26); " Compiled OK. monitor: loading monitor: monitoring (control-C to stop) [vs_0][fw_11] eth2:i[44]: 172.16.10.149 -> 192.168.1.89 (TCP) len=44 id=36544 TCP: 7480 -> 443 .S.... seq=25d68d6c ack=00000000 [vs_0][fw_11] eth2:I[44]: 172.16.10.149 -> 192.168.1.89 (TCP) len=44 id=36544 TCP: 7480 -> 443 .S.... seq=25d68d6c ack=00000000 [vs_0][fw_11] eth1:o[44]: 172.16.10.149 -> 192.168.1.89 (TCP) len=44 id=36544 TCP: 7480 -> 443 .S.... seq=25d68d6c ack=00000000 [vs_0][fw_11] eth1:O[44]: 172.16.10.149 -> 192.168.1.89 (TCP) len=44 id=36544 TCP: 7480 -> 443 .S.... seq=25d68d6c ack=00000000
To see a one-way network flow:
You can check the traffic to a source and destination in one direction:
fw monitor -e “accept (src=x.x.x.x and dst=x.x.x.x); “
Example (from 173.16.25.44 to 192.168.2.134)
CP-Firewall> fw monitor -e "accept (src=173.16.25.44 and dst=192.168.2.134); " monitorfilter: Compiled OK. monitor: loading monitor: monitoring (control-C to stop) [vs_0][fw_0] eth3:i[64]: 173.16.25.44 -> 192.168.2.134 (TCP) len=64 id=0 TCP: 31668 -> 443 .S.... seq=334241eb ack=00000000 [vs_0][fw_0] eth3:i[64]: 173.16.25.44 -> 192.168.2.134 (TCP) len=64 id=0 TCP: 10589 -> 443 .S.... seq=96f7c1ab ack=00000000 [vs_0][fw_0] eth3:i[64]: 173.16.25.44 -> 192.168.2.134 (TCP) len=64 id=0 TCP: 59589 -> 443 .S.... seq=b00da993 ack=00000000 [vs_0][fw_0] eth3:i[64]: 173.16.25.44 -> 192.168.2.134 (TCP) len=64 id=0 TCP: 24452 -> 443 .S.... seq=b7eab2df ack=00000000 [vs_0][fw_0] eth3:i[71]: 173.16.25.44 -> 192.168.2.134 (TCP) len=71 id=0 TCP: 24452 -> 443 F..PA. seq=b7eac473 ack=aaeba7f0 [vs_0][fw_0] eth3:i[71]: 173.16.25.44 -> 192.168.2.134 (TCP) len=71 id=0 TCP: 31668 -> 443 F..PA. seq=33425c0a ack=39f1e2fa [vs_0][fw_0] eth3:i[71]: 173.16.25.44 -> 192.168.2.134 (TCP) len=71 id=0 TCP: 59589 -> 443 F..PA. seq=b00db2f8 ack=5c949cea [vs_0][fw_0] eth3:i[71]: 173.16.25.44 -> 192.168.2.134 (TCP) len=71 id=0 TCP: 10589 -> 443 F..PA. seq=96f7c6d9 ack=9c027709 monitor: caught sig 2 monitor: unloading CP-Firewall>
To see a 2-way network flow:
You can check the traffic to a source and destination in both directions:
fw monitor -e "accept (src=x.x.x.x and dst=x.x.x.x) or (src=x.x.x.x and dst=x.x.x.x);"
Example (from/to 172.16.125.81 to 192.168.1.84)
CP-Firewall> fw monitor -e "accept (src=172.16.125.81 and dst=192.168.1.84) or (src=192.168.1.84 and dst=172.16.125.81);" monitorfilter: Compiled OK. monitor: loading monitor: monitoring (control-C to stop) [vs_0][fw_17] bond1.102:i[84]: 192.168.1.84 -> 172.16.125.81 (ICMP) len=84 id=52498 ICMP: type=8 code=0 echo request id=22608 seq=1 [vs_0][fw_17] bond1.102:I[84]: 192.168.1.84 -> 172.16.125.81 (ICMP) len=84 id=52498 ICMP: type=8 code=0 echo request id=22608 seq=1 [vs_0][fw_17] bond1.101:o[84]: 192.168.1.84 -> 172.16.125.81 (ICMP) len=84 id=52498 ICMP: type=8 code=0 echo request id=22608 seq=1 [vs_0][fw_17] bond1.101:O[84]: 192.168.1.84 -> 172.16.125.81 (ICMP) len=84 id=52498 ICMP: type=8 code=0 echo request id=22608 seq=1 [vs_0][fw_4] bond1.101:i[84]: 172.16.125.81 -> 192.168.1.84 (ICMP) len=84 id=24621 ICMP: type=8 code=0 echo request id=13742 seq=30840 [vs_0][fw_4] bond1.101:I[84]: 172.16.125.81 -> 192.168.1.84 (ICMP) len=84 id=24621 ICMP: type=8 code=0 echo request id=13742 seq=30840 [vs_0][fw_4] bond1.102:o[84]: 172.16.125.81 -> 192.168.1.84 (ICMP) len=84 id=24621 ICMP: type=8 code=0 echo request id=13742 seq=30840 [vs_0][fw_4] bond1.102:O[84]: 172.16.125.81 -> 192.168.1.84 (ICMP) len=84 id=24621 monitor: caught sig 2 monitor: unloading CP-Firewall>
As you can see, this is a very helpful and flexible command, you can combine the OR and AND operators as you need and capture the information into a .pcap file and analyze it later with Wireshark.
Thank you to Juan Ochoa for his work on this article.
Key takeawaysKey takeaways are generated with AI assistance. Because automated summaries can occasionally contain errors or miss important context, always refer to the full blog post for complete information.This article explains how to use Check Point's fw monitor command as an alternative to SmartView Tracker for inspecting traffic through a firewall, including clustered and SecureXL environments. It covers commands to verify active cluster members, temporarily disable SecureXL, and capture traffic for specific hosts or networks using capture points (pre-inbound, post-inbound, pre-outbound, post-outbound). The guide highlights constructing one-way and two-way capture filters, using logical operators, and saving captures to .pcap files for later analysis in Wireshark, improving troubleshooting precision and operational visibility.
How do I verify which cluster member is active before running fw monitor?
To determine which cluster member is active before running fw monitor, use the Check Point cluster command cphaprob state. This command reports the HA state of the member, allowing you to confirm that fw monitor will observe traffic on the active firewall. Because fw monitor shows traffic only on the active unit in a cluster, verifying active status with cphaprob state ensures you capture the correct traffic path for troubleshooting.
What are the fw monitor capture points and what do they indicate?
fw monitor uses four capture point indicators shown in captures as i, I, o, and O. Lowercase i (pre-inbound) captures packets before inbound processing, uppercase I (post-inbound) captures after inbound processing, lowercase o (pre-outbound) captures packets before outbound processing, and uppercase O (post-outbound) captures after outbound processing. These points let you see how packets traverse the firewall processing pipeline and help identify where policies or network behavior affect traffic flow.
How can I capture traffic for a specific host or network and analyze it later?
To capture traffic for a specific host, run fw monitor with an accept filter: fw monitor -e “accept host(x.x.x.x);”. To capture a network, use a network/mask expression (a /32 works like a host). For one-way flows, filter with src and dst: fw monitor -e “accept (src=x.x.x.x and dst=x.x.x.x);” and for bidirectional flows use OR to include both directions. You can combine AND/OR operators as needed and redirect output to a .pcap file, then open that file in Wireshark for detailed offline analysis.
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