Losing IPv6 gateway

[nug]

I'm having some difficulties with IPv6 on my AC68U running Asuswrt-Merlin 378.56_2. The router receives an IPv6 address from my ISP fine (Native with DHCP-PD) and my computer is assigned an IPv6 address from the router.
However shortly after startup (5-10 minutes) my computer loses the IPv6 gateway and DNS. It still has its Link-local IPv6 address though.

Is this an issue with the router or my PC? I was having issues on the PC before with MTU packet size but I think I managed to fix this by modifying Windows firewall to accept all ICMPv6 packets.

 

[charlie2alpha]

Are you using ethernet or Wi-Fi to connect to the router? I'm saying this because several times something similar has happened to me when using Wi-Fi, but not with an ASUS router. The common thing in both cases though seems to be dnsmasq, which I use in the my router here at my work place and the ASUS firmware that uses it too. dnsmasq is the software responsible for DSN and IPv6 setup on ASUS routers.

 

[nug]

I'm using ethernet to connect to the router.

 

[charlie2alpha]

Oh, also, if you have access to the router via ssh or telnet, try to issue this command when it happens:

 service restart_dnsmasq

And see if the IPv6 is restored.

 

[nug]

That seems to have renewed the IPv6 gateway.

 

[charlie2alpha]

Interesting. Something seems to cause dnsmasq not to advertise the IPv6 correctly. Could be a bug in dnsmasq itself since it has happened to my custom build router here. I use version 2.75 of dnsmasq, @RMerlin uses the same version in his firmware.

 

[nug]

Thanks for the help charlie2alpha. Since restarting dnsmasq I haven't yet lost the IPv6 gateway on the computer but I haven't restarted or turned the PC off yet.

 

[charlie2alpha]

Theoretically turning on/off or rebooting the PC itself should not affect anything but I guess you'll find out eventually.

 

[nug]

Perhaps if the router restarts then dnsmasq may start playing up again?

 

[charlie2alpha]

Perhaps if the router restarts then dnsmasq may start playing up again?

That's a possibility. Best course of action for now, keep an eye on how it behaves.

 

[PabloAbonia]

UPDATED/CORRECTED
I've found that this typically occurs at startup, and what is happening is an absence of router announcements. iOS apps such as "Discovery" can demonstrate if a router announcement can be detected.

At start-up there are always 2 competing instances for dhcp-event. This is because in a dual-stack IPv4/IPv6 environment there are two (?I think?) dhcpd running, and each will send a "bound" event. Therefore, I use the dhcp-event script to wait for the WAN IPv6 address to be assigned, and for the router to start by waiting for hour.pid(?) file to be set. Then I kill off dnsmasq and restart, so that it gets a variety of internally assigned IPv6 addresses. Kill -HUP doesn't quite work for it.

I'm forced to do this as TWC does prefix delegation with changes in the prefix occurring with reboots of the router or the cable modem. This prevents me from assigning a stable hostname without updating the prefix in the hosts file at the change in the IPv6 prefix. I use the dhcp-event script for that.

Pablo