Long story short

It says the default is both 10 seconds, and forever.

ttl_dns_cache (int) –
expire after some seconds the DNS entries, None means cached forever. By default 10 seconds.

By default DNS entries are cached forever, in some environments the IP addresses related to a specific HOST can change after a specific time. Use this option to keep the DNS cache updated refreshing each entry after N seconds.

Expected behaviour

One answer :)

Where

https://github.com/aio-libs/aiohttp/blob/master/docs/client_reference.rst line 948 (doesn't render fully in the github preview)

Why don't I just fix it

I don't have all the sphynx stuff set up, and it's so small I'm not going to go through all that. Sorry :)