C6900 Cable Modem with custom DNS settings not passed on to DHCP network clients

Question

I actually have a&nbsp;NETGEAR C6900 / AC1900 Cable Modem Router.&nbsp;I have configured the C6900 as a DHCP server, and with custom DNS server settings (i.e. not getting DNS servers automatically from the ISP). The problem is that while all network clients configured to get their IP addresses and DNS servers automatically via DHCP from the gateway (the C6900), they ARE being given proper IP addresses, but they are NOT being given the DNS servers configured on the C6900, but rather DNS servers from the ISP (even though the C6900 itself isnt using the DNS servers from the ISP). Note that I also have Parental Controls enabled through OpenDNS as the instructions dictated, which requires using OpenDNS DNS servers (which is how the C6900 is configured). If DHCP clients on the network are not getting the OpenDNS DNS server settings that have been configured on the C6900, then theres no purpose in parental controls, because the DNS lookups being done by network clients are not going to OpenDNS and getting logged -- they are going to the ISPs DNS servers instead. How do I ensure that DHCP clients not only receive an IP address from the C6900, but its DNS server settings too?

vkdelta · Answer

Please post your FW version and screenshots of your configuration.&nbsp;&nbsp;&nbsp;&nbsp;

brado77 · Answer

I have further diagnosed the problem, and here's some more details:&nbsp;&nbsp;When parental controls are enabled, the router does *not* pass its configured DNS servers to clients (either those obtaining DNS servers automatically or those configured with the gateway router's IP address as its static DNS server). Instead, it passes the ISP's automatically detected DNS servers to clients. This is viewable in the client's DNS settings after an IP address is acquired, and from performing an nslookup from the client -- it uses the ISPs DNS servers, not the configured servers on the router. That is an outright bug.&nbsp;When parental controls are disabled, and the router has configured custom DNS servers, it *does* pass the configured IPv4 DNS servers to clients&nbsp;(either those obtaining DNS servers automatically or those configured with the gateway router's IP address as its static DNS server).&nbsp;However, it *also* passes IPv6 DNS servers which are automatically acquired from the ISP to those same clients, and when a domain name is resolved, the IPv6 servers from the ISP are used, not the IPv4 DNS servers configured on the router. I have not found a way to either turn IPv6 off on the router, or to configure custom IPv6 DNS server addresses. This appears to be another bug.&nbsp;The use case here is simple: if you configure the gateway router to use custom DNS servers instead of the DNS servers obtained automatically from the ISP,&nbsp;clients obtaining DNS settings automatically from the gateway router&nbsp;should perform their lookups against the custom DNS servers, not against the ISPs DNS servers.&nbsp;&nbsp;I'd classify these bugs as major (or severe, whatever) as they result in a network-wide loss of intended functionality. This loss of functionality prevents easy problem resolution if the ISP's DNS servers go down and you need to point clients elsewhere, or using other DNS servers for performance or filtering reasons. Netgear's Parent Controls are very limited and don't appear to completely work (but that's an entirely separate conversation -- I tested that for hours too), and so using a separate third party filter is a comon need. (ironically, going direct to OpenDNS rather than through the router's configuration seems a better option). But unfortunately, the router's behavior prevents this.&nbsp;The only resolution I can find to solve this (barring some answer / fix from Netgear), is to run a completely separate DNS server, and point clients at it instead, which is completely redundant and unnecessary -- the router should handle this simple behavior.&nbsp;

gelogg · Answer

I too have the same situation using C3000 with Open DNS.&nbsp;Is there a telnet daemon running on the device we can login to. Id like to essentially hardset the ipv6 DNS hosts given out by dhcp.&nbsp;&nbsp;Since there is no option to set those values for clients I get the ISP values.&nbsp;Alternatively (and i doubt thism call it a lack of faith) : but perhaps is it known to be possible to have comcast push those settings down to the router via a config file or some such thing?

antinode · Answer

&gt; [...] Is there a telnet daemon running on the device [...]&nbsp;&nbsp; Probably not normally, but you could try one of the Netgear TelnetEnable programs floating around out there (I use the one which I'vemodified: http://antinode.info/nte ).&nbsp; Whether you can get the desiredalterations applied is a different question, of course.

Forum Discussion

C6900 Cable Modem with custom DNS settings not passed on to DHCP network clients