RT-BE88U: IPv6 routing fails for LAN clients

[JaneuX]

Hi,

I’m dealing with an IPv6 issue where addressing works, but routing from LAN
clients does not.

In short:
The router itself has full IPv6 connectivity, and all LAN clients receive valid
global IPv6 addresses and a default route, yet IPv6 traffic from LAN clients
does not reach the internet.

This looks like a case where IPv6 address assignment works correctly,
but IPv6 forwarding from LAN to WAN fails.

What I already checked / tried:
- ICMPv6 is allowed (RA, NS, NA, echo)
- IPv6 forwarding is enabled
- Firewall FORWARD chain allows br0 → WAN
- MTU tested (1500, lower values tested as well)
- WAN interface has a global IPv6 address
- Prefix delegation works
- Tried ISP DNS vs custom DNS (no change)
- Router and Modem Hardreset (nothing worked)
- Same behavior with passthrough AND native IPv6

Key observations:
- Router IPv6 connectivity works
- LAN clients receive global IPv6 addresses and have a default IPv6 route,
but IPv6 traffic from LAN clients does not reach external networks.

Has anyone encountered a similar situation or can help identify
what part of the IPv6 routing path is likely broken here?

 

[killweav]

Not an Ipv6 expert by any means.

What does the score on this site say?
https://test-ipv6.com/

PS: I don't use IPv6 so I get a zero score.

Hope this helps.

 

[Ripshod]

Interesting.
What firmware you using?
You can see from my signature I'm running the same router with Merlin firmware, and a quick test has shown IPv6 addresses are routed correctly to the WAN.
I will point out that my ISP favours IPv6 connections over IPv4.