DNS caching in linux

Question

I am confused about DNS caching  I am writing a small forward proxy server and want to use OS DNS cache on a Linux system   If I understand correctly  then there is DNS caching at the browser level  Then there is DNS caching at OS level  Windows has it  I am not sure if Linux distros have it by default     So  how does a browser proxy server use OS DNS caching  I am trying to find if I can rely on Linux for DNS caching instead of doing it on my own inside my proxy   Thanks

User · Answer

Firefox contains a dns cache  To disable the DNS cache    Open your browser Type in about config in the address bar Right click on the list of Properties and select New   Integer in the Context menu Enter  network dnsCacheExpiration  as the preference name and 0 as the integer value   When disabled  Firefox will use the DNS cache provided by the OS

User · Answer

Here are two other software packages which can be used for DNS caching on Linux    dnsmasq bind   After configuring the software for DNS forwarding and caching  you then set the system s DNS resolver to 127 0 0 1 in  etc resolv conf   If your system is using NetworkManager you can either try using the dns dnsmasq option in  etc NetworkManager NetworkManager conf or you can change your connection settings to Automatic  Address Only  and then use a script in the  etc NetworkManager dispatcher d directory to get the DHCP nameserver  set it as the DNS forwarding server in your DNS cache software and then trigger a configuration reload

User · Answer

On Linux  and probably most Unix   there is no OS-level DNS caching unless nscd is installed and running  Even then  the DNS caching feature of nscd is disabled by default at least in Debian because it s broken  The practical upshot is that your linux system very very probably does not do any OS-level DNS caching   You could implement your own cache in your application  like they did for Squid  according to diegows s comment   but I would recommend against it  It s a lot of work  it s easy to get it wrong  nscd got it wrong      it likely won t be as easily tunable as a dedicated DNS cache  and it duplicates functionality that already exists outside your application   If an end user using your software needs to have DNS caching because the DNS query load is large enough to be a problem or the RTT to the external DNS server is long enough to be a problem  they can install a caching DNS server such as Unbound on the same machine as your application  configured to cache responses and forward misses to the regular DNS resolvers

User · Answer

You have here available an example of DNS Caching in Debian using dnsmasq  Configuration summary   etc default dnsmasq   Ensure you add this line DNSMASQ OPTS  quot -r  etc resolv dnsmasq quot    etc resolv dnsmasq   Your preferred servers nameserver 1 1 1 1 nameserver 8 8 8 8 nameserver 2001 4860 4860  8888   etc resolv conf nameserver 127 0 0 1  Then just restart dnsmasq  Benchmark test using DNS 1 1 1 1  for i in  1  100   do time dig slashdot org  1 1 1 1  done 2 gt  amp 1   grep  real   sed -e s   m     awk   sum     1  END  print sum   NR    Benchmark test using you local cached DNS  for i in  1  100   do time dig slashdot org  done 2 gt  amp 1   grep  real   sed -e s   m     awk   sum     1  END  print sum   NR

[linux] DNS caching in linux

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