Recommendations on cable modems for Cox that can handle IPv6

  • BLUF: Any suggestions on a cable modem that works with Cox and will delegate subnet prefixes to a pfsense firewall that is asking for it?

    I received some very competent help on this forum to address my inability to get a pfsense firewall behind a Cox Cable Modem to hand out IPv6 IP addresses on the LAN side. The Cox cable modem (ARRIS) shows a /60 block of IP address space being allocated on the WAN side. It is using a /64 slice on the LAN side and properly handing out IP addresses. ping6 and everything works for a machine directly connected to the cable modem.

    The problem is that it won't delegate one of the slices of /64 space to my pfsense firewall. The pfsense firewall is seeing the available subnets and asking for a /64 prefix to use on the LAN side, but it is not getting it. Based on the help I received below, I think my firewall is properly configured.

    I called COX and was told:

    1. We don't offer IPv6 unless the IPv4 address space is exhausted. This is after I specifically called Cox and asked if they offered IPv6 residential service. They said yes.

    2. Then, after I explained the problem with getting a /64 slide, I was told that if I wanted a static IPv6 ip address, I needed a business account.

    3. Then, I was told they offered IPv6 ipaddresses for the cable modem, but did not support IPv6 dhcp6 service. I pointed out this rendered IPv6 connectivity useless, so this was dropped.

    4. Next, I was told that they handed out individual IPv6 addresses, but not subnets.

    The last turned into an explanation that I could buy a modem that would do that, but the residential rental cable modem did not provide this service. So, I figured I would ask if there is a modem router out there that people know works with Cox. Uggh!


  • LAYER 8 Netgate

    I have used a Motorola/Arris SB6190 and currently use a Netgear CM600. Neither have ever exhibited any IPv6 issues since Cox went native here in Las Vegas. Other regions may vary. My CM600 don't show anything about IPv6. Its just a dumb modem.

    Are you sure you're just dealing with a modem? Sounds like a router in which case you might need to enable a bridge or pass-through mode or something. Unfortunately Cox is going to be the best place to go for that info and we can see how helpful they are being. Maybe their forum?

    What I get from Cox is almost as good as a static. Almost. The have done a good job honoring the DUID and giving me the same prefix every time.

    I do not get a /64 on WAN. Pretty sure I posted what I get on your other thread.

    In a nutshell pfSense gets a link-local address and global-unicast/128 on WAN and a /56 Prefix Delegation. The default router is link-local.

    The Arris was just flaky. Pretty sure there's a class-action or something regarding those modems.

  • Thanks. I am not completely sure of the cause of my problems and Cox was unable to answer my questions.

    I am going to try to get HE tunnel working. If I cant, then we've identified a common problem. In the meantime, I can save money by not renting, so I will but a netgeat cable-modem. My ASSUS car modem has router functionality built in (dhcp, Ethernet ports, wifi), so I have been assuming it should be the device that gives a /64 slice from the /60 it shows in the WAN side. Since that seems not to be happening, I am hoping a new cable modem with router might work.

    As you can see, I am new at this, so my troubleshooting skills are iffy.

    Thanks again for all your help.

  • @obitori Any modem on the Cox currently approved list is going to handle IP v6 with no problems, if you want to use pfSense with it I'd stick to the straight modems and not use their gateways that have built-in routers and WiFi.

    My Arris 6183 is working fine here but it is only a 3.0 modem not a 3.1.

    Lots of discussion of bad modem choices (Puma chipset) and good choices on the DSL Reports Cox forum.

    Calling Cox support is usually wasted time, you call multiple times and get multiple answers that can't all be possible if you don't just get a "I dunno" so other than reporting outages I don't bother them.

  • I use a TC4400 cable modem. It's also ready for Docsis 3.1 und performs very well.

  • @stan-qaz @Derelict
    I bought the Netgear cm700 cable modem without a router and plugged it in. After a few reboots, it works like a charm. I plugged my pfsense fw directly into it and the pfsense firewall is distributing working IPv6 IP addresses on the LAN side. Now, I can play with stuff until I break something. :)

    I really appreciate all the help.


  • LAYER 8 Netgate


    Thanks for the report.

  • @mrsunfire

    Thanks for the recommendation. I went with a Netgear CM700 and it works!

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