Technical Tip: FortiOS port groups in high end platforms

In top-end FortiGates, for example, 1800F, 1801F, 2600F, 3400E, 3600E, 4200F, 4201F, 4400F and 4401F the majority of the physical interfaces are participating in port groups.

Port group can be easily noticed, over the physical interface itself, under the GUI's Network -> Interfaces section:

The above example is from a FortiGate-3600E, and it is easily possible to observe that port3 up to port6 belong to the same group.

A group consists of 4 ports, and the settings like interface speed, media type, and Forward Error Correction [FEC] are the same for all group interface members by default.

When the user changes one of the speed settings, FortiOS generates a warning message and changes the setting to be identical in the other 3 port group members as well.

For example, speed settings were changed only in port33:

config system interface

    edit port33
        set speed 25000full
    next
"port33-port36" speed and/or mediatype/FEC will be changed to 25000full due to hardware limit. 
Do you want to continue? (y/n)y

Then, all the other three ports in the same group were automatically configured with the same setting:

show system interface

    edit "port34"
        set vdom "root"
        set type physical
        set speed 25000full
    next
    edit "port35"
        set vdom "root"
        set type physical
        set speed 25000full
    next
        edit "port36"
            set vdom "root"
            set type physical
            set speed 25000full

        next

It will not be possible to remove or split the ports separately from the port group members, as it comes by design.

Note:

A port group will have the same speed across all its interfaces, due to hardware limitations.

If one interface is not part of an aggregate, it is allowed to change its speed, as long as it is possible to change the speed of all other interfaces of the port group.

As explained, FortiOS does not allow changes in the speed of an interface that is a member of an aggregate, so if other ports of the same port group are members of an aggregate, it will not be possible to change the speed of a physical interface that is not part of an aggregate. 

Changing the 'mediatype' option will not be forced on the rest of the group members.

Behavior change from v7.0.2 onwards:

As of v7.0.2, and device allows a 1G/10G speed option mixed for ports in the same port group.

Test results from 2601F running v7.2.10:

2601F # show system interface port29
config system interface
    edit "port29"
        set vdom "root"
        set type physical
        set mediatype sr
        set snmp-index 29
        set forward-error-correction disable
        set speed 10000full
    next
end

2601F # show system interface port30
config system interface
    edit "port30"
        set vdom "root"
        set type physical
        set mediatype sr
        set snmp-index 30
        set forward-error-correction disable
        set speed 10000full
    next
end

2601F # show system interface port31
config system interface
    edit "port31"
        set vdom "root"
        set type physical
        set mediatype gmii
        set snmp-index 31
        set forward-error-correction disable
        set speed 1000full
    next
end

2601F # show system interface port32
config system interface
    edit "port32"
        set vdom "root"
        set type physical
        set mediatype gmii
        set snmp-index 32
        set forward-error-correction disable
        set speed 1000full
    next
end

Below are the Interface groups for some hardware models:

1800F and 1801F:

• Interface groups: 25 - 28, 29 - 32, and 33 - 36.

2600F and 2601F:

• Interface groups: 17 - 20, 21 - 24, 25 - 28, and 29 - 32.

3300E and 3301E:

• Interface groups: 17-20, 21-24, 25-28.

3400E and 3401E:

• Interface groups: 3-6, 7-10, 11-14, 15-18, 19-22.

3500F and 3501F:

• Interface groups: 3-6, 7-10, 11-14, 15-18, 19-22, 23-26, 27-30.

3600E and 3601E:

• Interface groups: 3-6, 7-10, 11-14, 15-18, 19-22, 23-26, 27-30.

4200F and 4201F:

• Interface groups: HA1, HA2, AUX1, and AUX2, 1 - 4, 5 - 8, 9 - 12, and 13 - 16.

4400F and 4401F:

• Interface groups: HA1, HA2, AUX1, and AUX2, 1 - 4, 5 - 8, 9 - 12, and 13 - 16.