IPv6 relay mode fails after a few hours

Installing and Using OpenWrt
1

Hello,
My ipv6 address work well when I reboot openwrt. However, after a few hours, it do not work:

Ping 2606:4700:4700::1111 具有 32 字节的数据:
PING：传输失败。常见故障。
PING：传输失败。常见故障。
PING：传输失败。常见故障。
PING：传输失败。常见故障。

Let me show the network topology and more infornation:

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Openwrt is the subnetwork in ipv4, and it works well every time. Ipv6 setting is relay mode.

This problem confuse me a lot. And I try some methods to solve it:

First:
When it does not work, I find that ipconfig command can show ipv6 address. And I use route -A inet6 in openwrt. The output do not contain that ipv6 address. The root router does not contain that ipv6 address either.

And:
I try to log dhcpv6:

root@OpenWrt:~# cat /etc/dnsmasq.conf
log-dhcp
log-queries
log-facility=/tmp/dnsmasq.log

root@OpenWrt:~# /etc/init.d/dnsmasq restart
udhcpc: started, v1.36.1
udhcpc: broadcasting discover
udhcpc: no lease, failing

root@OpenWrt:~# cat /tmp/dnsmasq.log
cat: can't open '/tmp/dnsmasq.log': No such file or directory

I found that I could not get log, which confused me so much.

I wonder how to get dhcpv6 log so that I can find why my ipv6 do not work sometimes and if you know how to solve this problem, please help me. Thank u.

2

I find that if I run dnsmasq as root, it could log

cat /var/etc/dnsmasq.conf.cfg01411c
# auto-generated config file from /etc/config/dhcp
conf-file=/etc/dnsmasq.conf
dhcp-authoritative
domain-needed
localise-queries
read-ethers
enable-ubus=dnsmasq
expand-hosts
bind-dynamic
local-service
cache-size=1000
edns-packet-max=1232
domain=lan
local=/lan/
addn-hosts=/tmp/hosts
dhcp-leasefile=/tmp/dhcp.leases
resolv-file=/tmp/resolv.conf.d/resolv.conf.auto
stop-dns-rebind
rebind-localhost-ok
dhcp-broadcast=tag:needs-broadcast
conf-dir=/tmp/dnsmasq.d
user=**root**
group=**root**


dhcp-ignore-names=tag:dhcp_bogus_hostname
conf-file=/usr/share/dnsmasq/dhcpbogushostname.conf


bogus-priv
conf-file=/usr/share/dnsmasq/rfc6761.conf
dhcp-range=set:lan,192.168.89.2,192.168.89.254,255.255.255.0,24h
no-dhcp-interface=wan
no-dhcp-interface=wan
3

IPv6 relay relies on odhcpd and doesn't involve dnsmasq, so check this:

ubus call system board; uci show dhcp

You can also try comparing working and broken runtime configs:

ifstatus wan6; ifstatus lan
ip -6 address show; ip -6 route show table all

As an workaround, you can convert OpenWrt to a dumb AP.