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My server hosts 2 different websites which lately have been slow to load on browsers.

After looking at potential causes and solutions online, I came across this thread.

One of the advised solutions was to disable IPv6 which I'd like to try, however, As I have no proficiency in this area, I first want to make sure I understand exactly what this will do (what are the consequences of doing so), and if OK then know what is the safe way to do so without breaking my server/websites.

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    Disabling IPv6 is never a solution. Why would you want (a currently small but growing number of) people to be unable to reach your site? If something else happens to work when you disable it, that is a data point which can help you find and fix the real problem. Dec 11, 2020 at 14:53
  • I see what you mean, I will keep searching for the problem then. Thank you!
    – EmL
    Dec 11, 2020 at 14:57
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    You could try posting a question here about whatever the problem really is. Dec 11, 2020 at 14:58
  • The reason I haven't yet is because I feel like I still do not understand enough of what happened to try and ask it here (after having a previous question closed because of not providing enough detail I am refraining from doing so). All i know is that they previously fixed the slow access to the website by adding the google DNSs to the etc/resolv.conf file , but ever since a restart 3 weeks ago, now it is really slow again. (etc/resolv.conf file is still the same) we made sure of it, since we knew of this old "slow website" problem
    – EmL
    Dec 11, 2020 at 15:01
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    Performance problems can be in any component of a thing. End user browser, various networks, storage, web server tuning, databases, APIs, third party services, inefficient code... You - or someone at your organization - needs an understanding of the full stack to be able to identify suspect subsystems. And a test system to freely try things in. We don't have the knowledge of your environment to guide such an open ended question. Dec 11, 2020 at 18:00

2 Answers 2

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No, do not disable IPv6. It breaks things, turns users without v4 away, and makes more work for your future project to use IPv6.

A host with only IPv4 addresses and routes will serve web sites just fine without doing anything. v4 and dual stack hosts can still get to it.

You cite forum posts circa 2008. And even then disabling IPv6 was an uninformed shot in the dark, I see no v6 in use in their terminal output. Further, in the time since, IPv6 has gone from early adopters to mature and widely deployed.

Use web site performance analytics to measure what is slow. Tools exist to simulate real user load on a slow connection, or to instrument actual user performance in their browser. Use F12 browser developer tools, for example. Prove exactly which requests. Then trace requests through your web server stack and see what is involved in serving it.

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If IPv6 is misconfigured on your server, then it not only could be part of the problem, but it probably isn't serving anybody anyhow. A scan of the web server logs or a bit of network monitoring should show how many endusers, if any, are using IPv6 to reach you. If there seem to be few or none, then the diagnostic benefit of running without it for a trial period likely outweighs the cost. And if that fixes it, then conclude that there's some misconfiguration in your ipv6 setup that ought to be addressed.

I've had direct involvement with two incidents in which misconfigured ipv6 caused very significant performance issues. In both cases (and I'm going to go light on details) IPv6 appeared to be running, so applications attempted to use it, but it wasn't being properly routed, so the traffic timed out. A timeout for, say, a dns lookup on every mail message or every web request will kill performance for sure.

Swearing off IPv6 completely is a bit Luddite. The moral is: if it's enabled, make sure it's properly configured.

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