Delay in ipv6

[Roman Mamedov]

On Wed, 4 Jun 2025 16:53:33 +0200
Andre Tann <atann at alphasrv.net> wrote:

> Hi all,
> 
> I hope this is not offtopic here. If so, pls let me know a better place 
> for this question.
> 
> I configured wireguard to route both IPv4 and IPv6. Both protocols work 
> fine. But test-ipv6.com only gives 9/10 points because the browser does 
> not use IPV6 even though it is available.
> 
> Then I investigated a bit and found this:
> 
> ping -4 dns.google => ping sequence starts immediately
> ping -6 dns.google => .5 secs delay => ping sequence starts
> ping -6 dns.google => ping sequence starts immediately
> 
> i.e.: On the first try, ping6 takes longer, but the second time there is 
> no delay anymore.

Hello,

Which DNS resolvers do you use?
Try 8.8.8.8 or 1.1.1.1 at first, and then their v6 equivalents.

> I suspected DNS trouble, but pinging 2001:4860:4860::8844 shows the 
> exact same behavior: delay the first time, no delay next time.

This might be caused by DNS again, trying to resolve PTR record for the IP.

Recheck if "ping -n" starts in this case without a delay.

-- 
With respect,
Roman