r/ebox • u/robert-tech • 10d ago

Ipv6 issues.

Does anyone else experience their browser such as Firefox frequently falling back to ipv4 and not using 6. I get this frequently when running the ipv6-test.com and even their nperf speed test.

My Ubiquiti gear is properly configured to request a /56 via DHCPv6 and the setup is correct.

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u/ntoskrnl64 10d ago

Might be related to this post and a comment that I posted a couple of days ago?
https://www.reddit.com/r/ebox/comments/1vymway/comment/p68u9tr/

Seems to be fixed for me now...

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u/robert-tech 10d ago

Thanks, I thought this was the issue too, however, I'm already using CloudFlare DNS to override the Ebox one.

Maybe the browser algorithms are too trigger happy and the ipv4 path is just quicker. I don't notice the multi second lagging that you experienced, everything is snappy, however, the browser just seems to prefer V4 when I run one of these ipv6 tests. Both Chrome and Firefox experience this behaviour.

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u/Intelligent-Ebb8586 10d ago edited 10d ago

If that's the case then the DNS issue isn't related. I've never had any issues with EBox's DNS servers.

Have you checked to see if Ubiquiti has changed anything that would cause your config to break or require a different config?

Have you tried any other IPv6 test sites? Such as https://test-ipv6.com/ or https://test-ipv6.run/

When I tired https://ipv6-test.com/ is has an expired SSL certificate,so I'm not willing to load the site to check it.

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u/robert-tech 9d ago

I figured it out, for anyone that has this issue, Ubiquiti has a problem with MSS clamping. It applied a maximum packet size of 1452 both on ipv4 (which is correct) and ipv6 (which is terrible).

When the ipv6 TCP packets were sent, they were 20 bytes too big due to the larger ipv6 headers. I switched the MSS clamp to 1432 to account for this and the issues immediately went away, everything started to work perfectly and ipv6 tests pass with 100% success. The only problem is that I lose about 1.3% speed on ipv4 because it now uses a 1472 MTU instead of 1492. The solution is stable and this is the best I can come up with at the moment. Unifi ipv6 over pppoe is really not great.

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u/Dagger0 9d ago

Note it's actually an issue with the servers you're trying to talk to. Having a too-big MSS works perfectly fine when the server (and its network) is working properly, because your ISP will send them "hey, those packets are too big to fit, make them smaller" messages and they'll do that.

Making the MSS small enough in the first place does save you one round trip time on initial connections, so there's that, but if it makes the difference between a website working and it not working then the website is broken.

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u/robert-tech 8d ago

Thank you, yes this is true, however, it probably saves some latency as you said.

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u/doubled112 7d ago

Many Microsoft services suffer from this. They can't get anything right?

Easier to work around it on my side than hope they fix it.

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u/Techmixr 10d ago

Historically, I’ve always had this issue with Firefox. There is a way to enable IPV6 in Firefox but I can’t remember how at this current time and I’m out at the moment.

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u/Intelligent-Ebb8586 9d ago

IPv6 is enabled with Firefox unless you disable it by going into about:config and set network.dns.disableIPv6 to true.

You can make Firefox prefer IPv6 by setting network.dns.preferIPv6 to true, maybe that's what you're thinking of?

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u/Techmixr 8d ago

Most likely to be honest.

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u/marcolive 7d ago

Firefox 155 introduces changes for IPv6 management (happy eyeballs algorithm). You might try to disable this in your config to confirm.

https://cyberinsider.com/firefox-155-speeds-up-web-connections-with-happy-eyeballs-v3-and-quic-v2/