FS#4259 - Cannot reach public-facing service in LAN from LAN; only reachable from WAN

[openwrt-bot]

harpia:

====CONTEXT====
I run a publicly accessible web server at home, behind an OpenWrt router. The router has firewall rules allowing incoming connections to ports 80 and 443 (forwarding rules for ipv4; port access rules for ipv6).

====THE PROBLEM====
A recent snapshot upgrade made the web server unreachable from LAN using ipv4, while still being reachable from WAN. Ipv6 is unaffected and works as expected from both LAN and WAN.

====REPRODUCING====

1. Setup a web server inside your LAN network and confirm that it can be reached from outside. I use my phone's 4G connection for that.

2. Download https://downloads.openwrt.org/snapshots/targets/ramips/mt7621/openwrt-ramips-mt7621-tplink_archer-c6-v3-squashfs-sysupgrade.bin and move it to "/tmp" on the router that is already running OpenWrt.

3. Run "sysupgrade openwrt-ramips-mt7621-tplink_archer-c6-v3-squashfs-sysupgrade.bin" and wait for the device to reboot.

4. SSH into it as root, set a root password, apply any needed UCI configuration* and reboot.

5. See if you can reach the web server from inside the LAN using its public ipv4 address.

• I use a shell script to automatically configure everything using UCI commands. It defines DHCP hosts, firewall rules, PPPoE authentication, etc.

====DETAILS====
Device: TP-Link Archer C6 V3 (ramips/mt7621)
OpenWrt version: SNAPSHOT (r18754-f6a01d7f5c)

• Last working snapshot I used was from December 2021, but I don't have its snapshot number.

[openwrt-bot]

jow-:

Should be fixed by 2dd6777

[openwrt-bot]

harpia:

I forgot to add a step after number 3 in "REPRODUCING":

3.1. After the reboot, perform a factory reset by holding the reset button in the back of the router. A clean start.

EDIT: Thanks for the update.