Forcing computer to prefer IPv4 - bad?

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Forcing computer to prefer IPv4 - bad?

Postby Nash » Fri Jun 10, 2022 4:09 am

Recently, I moved houses and changes ISPs, and noticed that I now have an IPv6 address.

I had a lot of trouble opening ports to allow people to be able to connect to my GZDoom games, and after some trial and error, I noticed that, despite having the ports open from my router interface, people won't be able to connet to me unless I force my computer to prefer IPv4.

After I made that registry tweak, people could finally connect to my GZDoom host games. I don't understand why... before the tweak, they wouldn't be able to connect at all, and yes even when attempting to join my IPv4 address with the IPv6-preferred setting... after the registry tweak, my games become joinable.

Anyway, I was curious what are the downsides to forcing my computer to prefer IPv4 and if there'd be any long term problems.
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Re: Forcing computer to prefer IPv4 - bad?

Postby Rachael » Fri Jun 10, 2022 8:13 am

Long term, yes, there's a possibility you will have problems since we've been in general kicking the can down the road for widespread IPv6 adoption.

However, you won't have to worry about that probably for another couple of decades, at least.

You aren't missing much without IPv6, if you are disabling it completely. It has a flawed design in that IPv4 at least had memorable numbered addresses, whereas IPv6 is an example of too-much-too-quickly. And yes, some parts of the internet stop working when you have IPv6 enabled, since your computer will prefer to use it whenever it looks up a domain name - it's because transport providers and backbones have been extremely lazy and lackadaisical about keeping their routing tables properly maintained, and that leads to problems.

In general if we ditched IPv4 completely these would not be problems - the problems with IPv6 would work themselves out because we'd be forced to use it. However that is not the case, and with a working "contingency" so to speak it's a lot less of a urgency and necessity to keep it working.
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Re: Forcing computer to prefer IPv4 - bad?

Postby KynikossDragonn » Fri Jun 10, 2022 11:13 am

One problem you can come across when disabling IPv6 is when your DNS server doesn't give you IPv4 addresses when resolving a particular domain, but only a IPv6 address. CloudFlare's 1.1.1.1 tends to do this a lot and the only way around it is to use Google's 8.8.8.8 or any other DNS server that doesn't exhibit such behavior, and cache the IPv4 address that was resolved to.

I actually had to disable IPv6 because I had the opposite happening, I was unable to reach certain domain names (even whole swaths of the internet at large) because the IPv6 address was either not present or completely invalid. IPv6 adoption by most US ISP's especially ones operating in low key areas seems to be very problematic...

EDIT: I somehow made a horrible typo, sorry for the confusion...
Last edited by KynikossDragonn on Mon Jun 20, 2022 2:48 am, edited 1 time in total.
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Re: Forcing computer to prefer IPv4 - bad?

Postby Blzut3 » Fri Jun 10, 2022 3:16 pm

Although the pandemic has sped up IPv6 adoption, it indeed will be years yet before not having it will be a problem. These days it's less ISPs but corporate IT folks that are dragging their feet. Although my municipal ISP has had trouble rolling out IPv6 due to the lack of proper documentation.

That said, at least on Linux, GZDoom binds to an IPv4 socket. Not sure if Windows does something different, but I'm surprised enabling/disabling IPv6 makes any difference there.
Rachael wrote:It has a flawed design in that IPv4 at least had memorable numbered addresses, whereas IPv6 is an example of too-much-too-quickly.

If you want you can totally setup stateful DHCPv6 and give you some network sequential addresses in the fd00::/64 range. Then your addresses would be even shorter than IPv4's! It's technically frowned upon, but it's perfectly legal to do so.

If IP privacy is turned off (particularly for your private subnets, and yes it's normal in IPv6 for your machine to have multiple addresses) your IPv6 address is derived from the MAC address which means in practice self assigned static addresses which is pretty nice. Ultimately you're supposed to use DNS/mDNS instead of addresses, so complaints about IPv6 address format is hugely overblown by people who just hate change.

Now there is enough apathy about IPv6 that things aren't quite as simple as I make it out to be since there's a lot of half-hearted IPv6 implementations in networking software. All the protocols exist for things to work great, but there's a lot of software that neglects to implement various things. It's getting better, but for example my router was running non-LTS Ubuntu for awhile because systemd-networkd's DHCPv6-PD implementation got overhauled in the last year. I wouldn't be surprised if the reason things were in a bad state until fairly recently is a result of more ISPs rolling out IPv6 so now developers can actually test their code in production environments.
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Re: Forcing computer to prefer IPv4 - bad?

Postby Player701 » Mon Jun 20, 2022 1:07 am

KynikossDragonn wrote:One problem you can come across when disabling IPv4 is when your DNS server doesn't give you IPv4 addresses when resolving a particular domain, but only a IPv6 address.

IPv4 and IPv6 addresses are stored in different types of DNS records (A and AAAA respectively). The problem is likely on the client's side: if IPv4 is disabled, the client should not be requesting any A records in the first place (and the other way around in case of IPv6). However, disabling IPv4 is most certainly a bad idea since a lot of servers on the internet still don't have an IPv6 address. On the other hand, I've never heard of any public servers that are only available via IPv6, so turning it off is unlikely to break anything (at least at this time).

As a side note, I have a VPS with both IPv4 and IPv6 addresses, and I've never experienced any problems with DNS resolution there. However, it runs Linux and not Windows, so, once again, the problem most likely lies on the OS side.
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Re: Forcing computer to prefer IPv4 - bad?

Postby KynikossDragonn » Mon Jun 20, 2022 2:47 am

... how did I type "disabling IPv4" there, I meant to say "disabling IPv6"!

I've only had domains fail to resolve to a IPv4 address (but not a IPv6 address) from CloudFlare's "1.1.1.1". Google's "8.8.8.8" so far always seems to reliably return IPv4 addresses.
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Re: Forcing computer to prefer IPv4 - bad?

Postby Apprentice » Mon Jul 04, 2022 4:48 am

Nash wrote:Recently, I moved houses and changes ISPs, and noticed that I now have an IPv6 address.

I had a lot of trouble opening ports to allow people to be able to connect to my GZDoom games, and after some trial and error, I noticed that, despite having the ports open from my router interface, people won't be able to connet to me unless I force my computer to prefer IPv4.

After I made that registry tweak, people could finally connect to my GZDoom host games. I don't understand why... before the tweak, they wouldn't be able to connect at all, and yes even when attempting to join my IPv4 address with the IPv6-preferred setting... after the registry tweak, my games become joinable.

Anyway, I was curious what are the downsides to forcing my computer to prefer IPv4 and if there'd be any long term problems.

You could have contacted your ISP and asked for an IPv4 address, I did that as well and within 30 mins, I had an IPv4 address. IPv6 is nice but a lot of devices that exists today and which I have, don't support it which makes it a hassle to get a port forwarding working . . . :/
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