I know this is old thread, but this is for knowledge base.
To be specific, this is what I did, it works great!
I just combine it with entware, resulted in the following
Markdown (GitHub flavored):
```shell
mkdir -p /jffs/scripts
```Adding script to execute when mounting the usb
Markdown (GitHub flavored):
```shell
cat > /jffs/scripts/mountOpt
#!/bin/sh
# 1. mount the opt dir after every reboot
# 2. change dnsmasq ipv6 dns server
mkdir /tmp/opt
# where /dev/sdX# is your usb opt partition
mount /dev/sda1 /opt
# find and replace line
sed -i "s/dhcp-option=lan,option6:23,.*/dhcp-option=lan,option6:23,[fe80::3]/" /etc/dnsmasq.conf
# restart dnsmasq
killall dnsmasq && dnsmasq --log-async
```press ctrl+d to exit
Markdown (GitHub flavored):
```shell
chmod 755 /jffs/scripts/mountOpt
nvram set script_usbmount="/jffs/scripts/mountOpt"
nvram commit
```Restart the router, to verify the result use `sudo radvdump` in linux terminal to see RA message, you should get something like this
Markdown (GitHub flavored):
```shell
sudo radvdump
#
# radvd configuration generated by radvdump 2.18
# based on Router Advertisement from fe80::f22f:74ff:fec4:3415
# received by interface br0
#
interface br0
{
AdvSendAdvert on;
# Note: {Min,Max}RtrAdvInterval cannot be obtained with radvdump
AdvManagedFlag off;
AdvOtherConfigFlag on;
AdvReachableTime 0;
AdvRetransTimer 0;
AdvCurHopLimit 64;
AdvDefaultLifetime 600;
AdvHomeAgentFlag off;
AdvDefaultPreference medium;
AdvLinkMTU 1492;
AdvSourceLLAddress on;
prefix 2403:6200:xxxx:xxxx::/64
{
AdvValidLifetime 600;
AdvPreferredLifetime 600;
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr off;
}; # End of prefix definition
RDNSS fe80::3
{
AdvRDNSSLifetime 600;
}; # End of RDNSS definition
}; # End of interface definition
```
