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Since a couple of days, my machine experiences a delay when loading webpages. Rather than starting loading, the browser sits there for several seconds (around 5 or 10 seconds), seemingly doing nothing.

Chromium says "Resolving host..." in its status bar while waiting. Firefox says "Looking up [domain]" and after a few seconds "Performing a TLS handshake to [domain]..." before the page finally loads.

The loading process itself is not slow; this only happens on opening, not during loading of data. An online internet speed test also reveals that the speed is the same as normal (47 Mbps down, 56 Mbps up). And another computer in the same network (running a different OS) does not have the same problem.

Does anybody know what I can do to check what is wrong? I'm not running out of disk space. I cleared out my browsers' caches, but that hasn't helped. And now I don't know, e.g. which log file(s) to look in.

I found several things to check when I searched, such as Ubuntu 18.04 slow after 2019 update, but none that address this particular problem.

This is with Debian 9.12, KDE.

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  • Seems like slow dns response. Try dig example.com and take a look onto "Query time" section.
    – DevilaN
    Jun 24, 2020 at 20:06
  • The query time says 17 msec, but I don't know what that means. Opening example.com in the browser takes 5 sec.
    – Mr Lister
    Jun 24, 2020 at 20:20

1 Answer 1

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This is some kind of DNS problem. This can happen if you query the wrong name servers first. You can check that with tcpdump. Find out which servers are accessed first.

# assuming eth0 is your WAN interface
tcpdump -i eth0 -n udp port 53

Or you add a domain to /etc/hosts. If the delay disappears then the problem is the external DNS access.

If that does not affect the problem then /etc/nsswitch.conf may be the reason. Change the hosts line to

hosts:          files dns

and restart the browser.

The last possible reason that comes to my mind is the name service caching daemon (nscd). Check whether it is running on your system and disable it for checking whether that solves the problem.

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  • Sorry for taking so long. I didn't know what to do with the output of the tcpdump, which only said tcpdump: listening on enp0s25, link-type EN10MB (Ethernet), capture size 262144 bytes and then started waiting for something. But the hosts line in /etc/nsswitch.conf looked suspicious, it said files mdns4_minimal [NOTFOUND=return] dns, so I changed that by putting the dns right after files, and all works fine now. Thanks!
    – Mr Lister
    Jul 7, 2020 at 8:50

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