apache 2.2 - iPhone OS 11_3 http connection flood

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I have been trying to limit max TCP
connections to port 80 of my server coming from the same IP. I have used iptables for
this task:

-A INPUT -p tcp --dport
            80 -m conntrack --ctstate ESTABLISHED -m connlimit --connlimit-above 24 --connlimit-mask
            32 -j
            LOG_THROT

The
rule sends packets to my LOG_THROT chain where I log them and tcp reset the
connection.

The problem is that all the IP's
that get logged (overflooding 24 parallel http connection rule) and get found in
apache's access logs seem legit users with referrals from google, coming from standard
mobile ISP's like vodafone etc. What they all got in common is User agent and it is:

Mozilla/5.0
(iPhone; CPU iPhone OS 11_3 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko)
Version/
11.0 Mobile/15E148
Safari/604.1

I
was wondering if the new OS/Browser has a higher limit than standard 6 parallel conns,
does it maybe use some kind of preloading of the links found on the website and spawns
additional connections or is it a crawler of some sort spoofing the
UA?

If it is legit, what do you suggest for a
safe connection count limit? 50, 100?

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class="normal">Answer

Why don't
you tune your web and use HTTP/2 (eventual
HTTPS)

They both use single, multiplexed
connection, instead of multiple connections in HTTP1.x Domain sharding techniques are
not needed any more.