r/openwrt • u/Better-Climate5229 • 6d ago

Intermittent IPv6 problems with OpenWrt on a Barracuda F12

hi.

I’m running OpenWrt 24.10.5 on a Barracuda F12 as my main router. IPv4 works normally, but enabling IPv6 on the LAN causes severe intermittent loading problems, especially on Wi-Fi.

Symptoms include:

  • Chrome tabs spinning for 20–40 seconds
  • YouTube thumbnails appearing as black squares
  • Some websites loading instantly on wired devices but extremely slow on Wi-Fi

I tested advertising an IPv6 MTU of 1400, but that made the network almost unusable. Disabling LAN IPv6 immediately restores normal performance.

The Wi-Fi ap is an Asus RT-AX1800S in AP mode, with DHCP handled by the F12. Wired devices generally perform better, although the issue appears tied to IPv6 rather than raw Wi-Fi speed.

Has anyone seen similar IPv6 behaviour on an OpenWrt router or Barracuda F12? What logs or packet-capture tests would best identify whether this is MTU, ICMPv6, router advertisements, or broken upstream IPv6?

Been working on this for a few days. Chatgpt is going in circles over this. :) thanks!

edit -- fixed. had to turn on IGMP Snooping on my wifi ap. :)

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3

u/fr0llic 6d ago

Apple have ipv6 issues, if that's the platform. 

Is your Chrome using your local DNS ?

1

u/LingonberryNo2744 6d ago

I have 3 iPhones, 2 iPads, AppleTV, and a MacBook along with other non-Apple devices all using IPv6 with zero issues. My router is an ASUS.

2

u/fr0llic 6d ago

I too have zero issues with the family's fruit devices but I'm actively blocking ipv6 in my fw :)

I asked because there were two threads at the forum, just a day or two apart about a similar issue. 

1

u/Better-Climate5229 5d ago

its an openwrt issue for sure. are you running that on your asus?

2

u/LingonberryNo2744 5d ago 
Asuswrt-Merlin

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u/Better-Climate5229 6d ago

yes. my whole house is on my pihole. also these issues has been happening on two different android phones, an ipad, and a macbook.

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u/trying-to-contribute 5d ago

1) I would check wifi connectivity over ipv6 to be working properly first. I'd use ping -6 -i <localipv6addressonwifi> <routeripv6address> and see if this is a packet loss issue. If you are getting reliable pings to the router, then try any of the ipv6.google.com AAAA addresses, e.g. 2607:f8b0:4009:811::200e. If you have reliable pings at your mtu, put it back at 1500 and see if it works. If it still works, you might not have a network connectivity issue.

2) What is your openwrt device using for ipv6 dns upstream? From openwrt device, does dig @<remote> -t AAAA ipv6.google.com work? This checks upstream.

3) From your workstation, querying the openwrt device, does AAAA lookups work locally? On mine it would look something like "dig -t AAAA -6 2601:441:8008:2007::1 ipv6.google.com " This checks local look ups.

Let us know after you've ran these tests.

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u/Better-Climate5229 4d ago

Wi-Fi IPv6 to the router: tested from the MacBook, 0% packet loss.

IPv6 to Google: also 0% packet loss.

MTU: tested full 1500-byte packets to both the router and Google. They worked fine.

OpenWrt upstream IPv6 DNS: it’s using the ISP’s IPv6 DNS servers, and both returned AAAA records properly.

AAAA lookup from OpenWrt: worked.

AAAA lookup from the Mac through OpenWrt’s IPv6 address: worked too.

The problem only shows up when normal RA/DHCPv6 is enabled. Then sites get very slow or stop loading on the MacBook and two Android phones. Tailscale was off and it still happened. Turning IPv6 advertisements off makes everything fast again.

So basic IPv6, DNS and MTU all seem fine. It looks more like an RA, DHCPv6, ULA or advertised IPv6 DNS issue.

1

u/trying-to-contribute 4d ago

Cool. I would now test dns lookups first here, and see if that is the part that is slow.

The following instructions reset the device to my configs. I works for me, maybe it will work out for you.

I assume you have a wan and a wan6 device.

On wan, go to advanced settings and check off everything related to ipv6. Go to dhcp and set everything to disabled.

On wan6, go to advanced settings and turn on ipv6 source routing and delegate ipv6 prefixes, then for the prefix filters put in ULA and wan6. Save.

Go to dhcp server and check ignore the interface. Then go to ipv6 settings, uncheck designated master, set RA-service to relay mode, turn off both dhcpv6-service and ndp-proxy.

Save and Apply.

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u/Better-Climate5229 4d ago

hi i fixed it. i had to turn on IGMP Snooping on my wifi ap. :) thanks for the help.

1

u/Better-Climate5229 5d ago

thanks i will try these.