Debugging IPsec on FortiGate: Understanding the Debug Flow

When troubleshooting issues related to IPsec encryption, it can be helpful to enable debugging on your FortiGate device. The `diagnose debug ipsec` command is a powerful tool that allows you to gain insight into the inner workings of your FortiGate's IPsec functionality. In this article, we will explore how to use the `diagnose debug ipsec` command and its various options.

Matching and Conditions

The syntax for matching and conditions in the `diagnose debug ipsec` command is similar to that of other FortiGate commands. You can specify a combination of IP addresses, ports, and protocols to match specific traffic flows. For example:

* `port`: specifies the source or destination port(s) in the packet(s)

* `saddr`: specifies the IP source address(es) of the packet(s)

* `daddr`: specifies the IP destination address(es) of the packet(s)

* `vd-name`: limits debug output to a specific VDOM (Virtual Domain) by its name

Filtering Debug Output

To filter debug output, you can use the `diagnose debug flow filter` or `dia debug flow filter6` command. These commands allow you to set filters for specific traffic flows and display only relevant information.

For example:

* `diagnose debug flow filter port 22`: sets a filter to display only packets with source or destination port 22

* `dia debug flow filter6 saddr 192.168.1.100 daddr 2001:0db8::1`: sets a filter for IPv6 packets with source IP address 192.168.1.100 and destination IP address 2001:0db8::1

Policy Lookup

The `diagnose debug flow` command also allows you to perform policy lookup, which shows what security policies match traffic between specific IP addresses and ports. This can be useful for troubleshooting issues related to policy-based routing or access control.

For example:

* `diagnose debug flow saddr 192.168.1.100 daddr 2001:0db8::1 port 22`: performs a policy lookup for traffic from IP address 192.168.1.100 to IP address 2001:0db8::1, with source port 22

Security Rulebase Diagnostics

The `diagnose debug flow` command can also be used to perform security rulebase diagnostics. This allows you to troubleshoot issues related to security policy enforcement and identify potential configuration problems.

For example:

* `diagnose debug flow filter saddr 192.168.1.100 daddr 2001:0db8::1 port 22`: sets a filter to display only packets with source IP address 192.168.1.100, destination IP address 2001:0db8::1, and source port 22, and then performs security rulebase diagnostics.

In conclusion, the `diagnose debug ipsec` command is a powerful tool for troubleshooting issues related to IPsec encryption on FortiGate devices. By understanding how to use this command and its various options, you can gain valuable insights into your network traffic and troubleshoot problems more effectively.

Fortigate debug ipsec