Hot!Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER

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duetgroup_tech
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2020/05/19 07:49:47 (permalink)
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Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER

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.
 
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    mjcrevier
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    Re: Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER 2020/05/19 11:53:35 (permalink)
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    I saw similar issues with Netgear modems used by Comcast in the States. Wonder if they use the same hardware.
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    emnoc
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    Re: Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER 2020/05/19 12:27:53 (permalink)
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    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

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    duetgroup_tech
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    Re: Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER 2020/05/20 03:48:17 (permalink)
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    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".

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    emnoc
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    Re: Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER 2020/05/21 12:24:22 (permalink)
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    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
     

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    waterboy1602
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    Re: Fortigates incompatibility with Telenet DOCSIS 3.1 E-ROUTER 2020/05/28 09:44:42 (permalink)
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    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?
    #6
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