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Panderson
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DHCP and Cable modem

Tue May 16, 2017 1:59 pm

I know a Cable Modem (CM). Acts as both DHCP client on the WAN side and server on the LAN side. I know the the modem passes some information, such as name server, from WAN to the LAN client. Will the modem pass DHCP options such as option 43 to the LAN client. In this case I want to connect some wireless access points to the network using a Cable modem. I want to be able to pass option 43 through the to modem to the AP so the AP can learn its controller address.
 
notfred
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Re: DHCP and Cable modem

Tue May 16, 2017 2:06 pm

I suspect it will get through, but I suspect the DHCP option will be ignored by the ISP's DHCP server.
 
Captain Ned
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Re: DHCP and Cable modem

Tue May 16, 2017 2:31 pm

Just buy a router/AP combo and get the cable modem out of it. Why would I want my network MAC addresses upstreamed to Comcast?
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Panderson
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Re: DHCP and Cable modem

Tue May 16, 2017 9:01 pm

A little more information. We have a cable feed and a 100/100 fiber connection from our provider. In order to provide wireless to the entire area we are currently using a few bridged APs. Running new copper or fiber to those APs is simply not an option. We do have CATV available. We can use a cable modem to connect the AP to the backbone. However, the AP must be able to find the controller and rather than hard code the AP controllers IP address on the AP it would be nice to simply add Option 43 to the DHCP server which is co located locally with the CMTS.
So, back to the original question: are there any cable modems that will pass DHCP options from the WAN side to the LAN side?
Thanks...
 
notfred
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Re: DHCP and Cable modem

Tue May 16, 2017 10:18 pm

Run everything off the fibre link. Use MoCA Adapters https://www.newegg.ca/MoCA-Adapters/SubCategory/ID-3372 to use the cable wiring as Ethernet and disconnect the cable wiring from your ISP.

If you plug the APs in to the cable feed via a cable modem then they get DHCP from the ISP and so will not have the option 43 to tell them the controller.

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