I'm trying to figure this out, could you give more information/details/steps to DHCP option 121? I'm trying to find more information about it.FWIW, the best option for that type of setup (e.g., VyOS, pfsense) is DHCP option 121. You can either explicitly add a route to one different VLAN subnet via your router (e.g. 192.168.1.0/24 via the ve on your Brocade) or to an entire range, depending on the address ranges you’re using (e.g., 192.168.0.0/16 via the ICX).
With your internet-facing router set as the default gateway and on the same subnet, your devices will know it can reach the gateway directly, avoiding any asymmetrical routing issues.
Alternatively, which may not be the best idea as I haven't done it yet, I was thinking I could tag all the VLANs on a trunk that I want DHCP for within the switch, and connect it to the router on another dedicated port. On the router, I could have the DHCP server(s) bind to an IP/bridge within those VLANs which are tagged on that interface.
The idea keeps InterVLAN routing on the switch by keeping the gateway on the switch's `ve`, but would route those DHCP helper-ip requests to the actual DHCP server IP address - on the same VLAN (or perhaps the DHCP server could actually reach the broadcasts of that VLAN).
I don't know if that would work, because the router would have a different default route.