Troubleshooting Tip: Cannot access the FortiGate web admin interface (GUI)

Description

In some cases, it is possible to reach the FortiGate unit through a Ping, Telnet or SSH, but not through the web admin GUI.

This article discusses some possible causes for a non-working GUI access.

Solution

1) Interface settings

GUI access, HTTP and/or HTTPS, has to be enabled on the interface.

CLI commands:

# config system interface
    edit <interface name>
        set allowaccess ping http https
end

Possible allow access settings: PING, HTTP, HTTPS, TELNET, SSH, FGFM (FGFM is required for FortiManager access)

2) Trusted host configuration

If ‘trusted hosts’ are configured, IP address of the computer used for the GUI access must be allowed as “trusted host”. A whole subnet can be allowed as “trusted host”.

By default, trusted host settings are not configured, and administrative access is not restricted to any specific user IP addresses.

Sample trusted host configuration:

# show
    # config system admin
        edit “admin-test”
            set trusthost1 10.10.10.1 255.255.255.255
            set trusthost2 192.168.0.0 255.255.0.0
            set vdom “root”
                # config dashboard-tabs
            …

Changing the trusted host configuration:

# config system admin
edit <admin user>
set trusthost <1 to 10> <ip address>/<mask>
set ip6-trusthost <1 to 10> <ip6 address>/<mask>

Trusted host settings are per admin user, and are valid for all types of access.

Example: If a user is trusted for access through SSH, it is also trusted for HTTP or HTTPS access.

3) MTU along the path.

After the first few synchronization and handshake packets, the web admin GUI HTTP and HTTPS packets can become larger than 1500 bytes.

Example: When a FortiGate network interface is connected to a network segment that supports such extended size packets. For Telnet or SSH, packets typically remain of smaller size.

To be then able to use the web admin GUI, the fragmentation must be allowed at certain points in the network infrastructure (points, where a jumbo-frame reaches a network segment that does not support it), or Jumbo frames must be allowed along the whole communication path.

Note about Jumbo frames: Jumbo frames are packets that are larger than the standard 1500 maximum transmission unit (MTU) size. Jumbo frames increase data transfer speeds by carrying more data per frame, reducing the overhead from headers.

All networks that carry jumbo frames must have network devices that all support jumbo frames. Otherwise, jumbo frames will be dropped, when they reach network devices that do not support them.

4) Admin access ports.

By default, for admin login via GUI, the HTTPS port is configured to 443 and the HTTP port to 80.

If those default settings are changed, access to the GUI will not be possible without specifying the custom-port used at the end of the URL.

To verify which HTTPS/HTTP ports are configured for admin access:

# show full | grep admin-port
          set admin-port 80
                                                                         TestFGT # show full | grep admin-sport
          set admin-sport 443

In the event that the default ports have been changed, either directly access the GUI using the specific port that is currently defined:
http(s)://<address_of_appliance>:<custom port>

For example: http://192.168.0.101:222 where 222 is the non-default port used to access GUI via HTTP.

If the ports needs to be changed to a new value or the default value, use the following syntax for HTTP access:

# config system global
    set admin-port <integer>
end

Whereas for HTTPS access, use the syntax:

# config system global
    set admin-sport <integer>
end

5) admin-server-cert (for versions 5.6 and above only).

Enable the following debug and try to access the GUI again:

# diagnose debug application httpsd -1
# diagnose debug enable

If the output is matching the following:

[httpsd 1746 – 1552998712    error] log_error_core[439] — [Tue 19 12:31:52 2019] [crit] Can’t open certificate file /tmp/admin_server.crt, nor /ssl/certs//tmp/admin_server.crt
[httpsd 1749 – 1552998714    error] log_error_core[439] — [Tue 19 12:31:54 2019] [crit] Can’t open certificate file /tmp/admin_server.crt, nor /ssl/certs//tmp/admin_server.crt
[httpsd 1752 – 1552998716    error] log_error_core[439] — [Tue 19 12:31:56 2019] [crit] Can’t open certificate file /tmp/admin_server.crt, nor /ssl/certs//tmp/admin_server.crt

Proceed with the following:

# config sys global
set admin-server-cert Fortinet_Factory
end

6) Existing virtual IP is overriding admin HTTP or HTTPS ports.

When a Virtual IP (VIP) has the same IP address of FortiGate interface and forwarding the same ports used for HTTP/HTTPS access (example 80 or 443), the VIP will override the administrative access.

This should either be removed or changed such that it doesn’t overlap with FortiGate HTTP/HTTPS ports.

This can be verified by checking the VIP list on FortiGate (Policy & Objects -> Virtual IPs) or running the debug flow.

Refer to the KB article FD31702 referenced below.

7) Restart HTTPS Daemon

In case none of the processes above fixed the issue, please try to restart the HTTPS Daemon.

# dia sys process pidof httpsd

– Note the first listed process ID (this is the parent process).

# dia sys kill XX                                                    <—– Add the process ID gathered in step 1.

– This restarts httpsd

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