FG-100D DHCP NOT WORKING AFTER UPGRADE FROM 5.2.7 TO 5.6.8

[crangel]

Hello

I have a FG-100D  in release  5.2.7 connected to a stack of S4810 Dell switches with an vlan switch configured with some vlans as shown below. I have configured DHCP in some of the vlan iterfaces. This is working normal. I have an spare 100D which I upgraded to 5.6.8 because the new Forticlient licence is not compatible with 5.2.7. However when I put this upgraded FG-100D into production the whole network behind gets down because it is not able to get DHCP from Fortigate. I uploaded the same configuration to the upgraded fortigate however it is not working. Any ideas about why DHCP is not working on this upgraded Fortigate??

 THIS FORTIGATE IS WORKING FINE

[BrianB]

Was the spare 100D also running 5.2.7? If so did you follow the upgrade path?

5.2.7 > 5.2.9 > 5.4.4 > 5.6.2 > 5.6.6 > 5.6.8

[crangel]

 Thanks for replying Brian. yes it was. First we followed up an upgrade path suggested by Fortinet Technical support 5.2.7 > 5.2.9 5.2.9 > 5.4.4 5.4.4 > 5.4.5 5.4.5 > 5.6.2 5.6.2 > 5.6.6 5.6.6 > 6.0.4

The we realized that it was not working as with 5.2.7. After reading your post, I stared over again with your suggested upgrade path, however when in 5.4.4 I realized that my VLAN switch I used to have in 5.2.7 - 5.2.9 dissapears in 5.4.4 and becomes a hardware switch which I believe is the issue. I am not a network expert but from what I know this should be a vlan switch or an 803ad aggregate in order to allow communication from my vlans to the Fortigate DHCP servers interfaces. Again this is working fine with the FG-100D in 5.2.7.