Sky ER110 Router and IPv6

Hi there I am using a Sky ER110 router. One of the options is the ability to disable IPv6 LAN side on the router. Despite IPv6 LAN side set to disabled and IPv6 DHCP server unticked I am getting a CCTV DVR showing with a intermittent IPv6 address. The IPv6 address doesn't fluctuate, it's as though it has been manually configured with a static IPv6 address. Despite all the LAN side IPv6 disabled on the router I can still ping this IPv6 address via the router's interface with no packet loss! This CCTV box has been purposely set with a false IPv4 gateway address together with being disabled in the router's firewall. In addition to this everytime I try and ask for the DVR's IPv6 configuration via the DVR's interface it comes back with a get configuration failed message. I am wondering if access to this applet has been disabled somehow. Can anyone shed any light on any of the above please...

Does the CCTV DVR IPv6 address start with fe80 or fdxx or a global 2xxx?

All interfaces can self-assign an IPv6 address (by design) but that doesn't mean it is globally route-able.

More importantly, does the CCTV DVR IPv6 configuration show a default gateway? Irrespective of the type of IPv6 address being assigned, if a device doesn't have a route to / from the rest of the Internet, it is not really on the Internet, even if is pingable from the router itself (or any other device on the same link-local network).

Devices only obtain information about the default gateway if they are either configured with one statically or (more usually) receive it from a router advertisement (RA).

If a device has previously received a RA which has then gone away, the IPv6 address becomes tentative/provisional before it is removed completely, because the design makes allowances for intermittent faults which may be recovered within a configurable time interval.

Also, you mention the DVR has been configured with a false IPv4 address for its gateway. This is a common misconception but the address should be removed or left blank as otherwise the DVR will constantly be trying to contact this fake address (for any destinations not on the local subnet).

For a standalone network where you don't want something to talk to other networks it is both valid and desirable to have no gateway assigned and UIs which force you to enter a gateway address are at fault.
Likewise real DHCP servers can also be configured to assign IP addresses with or without DNS settings and with or without gateway address (it is not all or nothing), so some consumer routers which don't provide this option are also lacking.

I only mention this because you could ultimately solve both questions by placing the DVR (or all the CCTV devices) behind a real router and even provide desired configuration (both IPv4 and / or IPv6) by DHCP, if the Sky Router is limiting your options.

Edited by prlzx (Wed 16-Jan-19 21:06:31)

I can confirm that the IPv6 address starts with fe80: I am unable to check for a gateway address as the DVR returns a error message when I try to get it to display through its GUI. Thank you for your quality input by the way

In which case that is a link local address and can't be accessed outside your network.

Thank you, that has been very helpful/reassuring Do you know why I am able to ping the IPv6 address though if IPv6 LAN side has been disabled on the router? TIA

It is because you are trying to ping a link local address from the routers own link local address. I suspect disabling IPv6 just stops the router assigning a global unique prefix to the interface not actually to disable the protocol.

I think you are almost certainly right there. Thank you once again