Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER

[duetgroup_tech]

Hello all.

If you are using a Fortigate with the Belgian Cable ISP Telenet, you should know that there is a known incompatibility between Fortigates and the new Telenet DOCSIS 3.1 E-ROUTER. This is the kind of router that they install for all new clients. For now, it is possible to request Telenet to install a DOCSIS 3.0 modem and that solves the issue, but going forward this could become a big problem, especially if they require all their clients to switch to DOCSIS3.1.

The problem seems to be that Fortigates don't support Unicast DHCP. 

As far as I can tell the incompatibility is known to Telenet, but I don't know if Fortinet knows or not. I have opened a TAC case to find out.

[mjcrevier]

I saw similar issues with Netgear modems used by Comcast in the States. Wonder if they use the same hardware.

[emnoc]

Can you explain unicast DHCP? The whole purpose of DHCP is the client has no "address" so how is unicast used here? Outside of a DHCP-relay concept, DHCP is broadcasted 

Ken Felix

[duetgroup_tech]

From what I understand, "Unicast DHCP" is a misnomer.

Unicast refers to the Broadcast flag set in the Bootp flags. The Fortigate sets it to "Broadcast", whereas regular Windows/MacOS clients set it to "Unicast".

[emnoc]

Interesting i would have to capture a DHCP datagram,  but broadcast and unicast just determines  the action of the DHCP-offer as 0.0.0.0 or x.x.x.x in  the offer from my understanding.

In the above you would need to look at the offer and witness is being set imho. I would use a dhcp-tool to test the above with the ISP and see what's happening or grab the difference 2 or more different devices for comparison.

Ken Felix

[waterboy1602]

Hi,

I'm experiencing exactly the same problem. Did you already found a fix for this or did you just change your modem with a DOCSIS 3.0 one?

I just swapped my DOCSIS 3.0 for a 3.1 one, but didn't do enough research to find this before hand. Can I possible fix this with the 3.1 modem?

[avka1453]

Hi,

Does anyone know if this issue has been resolved with a fortinet update?

thanks

[waterboy1602]

I can tell you that in the mean time this bug has been fixed. I'm using a DOCSIS 3.1 E-ROUTER from Telenet with a Fortigate firewall myself and the bridging functionality works without flaws.

[avka1453]

That's great! Which version are you on?

Kind regards,

[waterboy1602]

Any idea how I can find on which version I am?