Upgrade OpenWrt

Connect to device via ssh:
```
ssh root@192.168.1.1
```

Configure default dns resolver ↕

config dnsmasq
...
# Set default dns resolver
list server '127.0.0.1'
# Enable usage of dns resolver from /etc/resolv.conf
option noresolv '-1'
# Disable DNSSEC validation
option dnssec '-1'
option dnsseccheckunsigned '-1'

2.2. Configure /etc/config/network

# IPv4
config interface 'wan'
        ...
        # Keep peer DNS enabled to improve your DNS fault tolerance.
        option peerdns '-1'
        # Use digitalcourage as dns resolver
        option dns '5.9.164.112'

# IPv6
config interface 'wan6'
        ...
        # Keep peer DNS enabled to improve your DNS fault tolerance.
        option peerdns '-1'
        # Use digitalcourage as dns resolver
        option dns '2a01:4f8:251:554::2'

2.3. Reload configuration and restart dnsmasq:

reload_config
/etc/init.d/dnsmasq restart

Stubby won’t be installed after upgrade, which would result in broken dns!

Download sysupgrade image (here fritzbox 7530 23.05.5):

wget https://downloads.openwrt.org/releases/23.05.5/targets/ipq40xx/generic/openwrt-23.05.5-ipq40xx-generic-avm_fritzbox-7530-squashfs-sysupgrade.bin  -O /tmp/sysupgrade.bin

Execute system sysupgrade:

sysupgrade -v /tmp/sysupgrade.bin

This preserves any old configuration files. If they should be wiped use `-n` option

Make sure custom firmware (e.g. for the dsl modem) is still installed!!