DNS is the system which is used to convert human-readable hostnames (such as
example.com) into the IP addresses that are actually used to contact the services running upon them.
If you’re running applications that require the lookup of a large number of IP addresses the single best thing you can do is deploy a local DNS-cache.
Many services perform DNS lookups, including webservers and log-analyzing software, and mail-servers.
NOTE: Mail-servers might perform significantly more DNS lookups than you expect if you’re using a DNS-based blacklist for rejecting SPAM at submission-time.
One of the simplest DNS dedicated DNS-caches is pdnsd, this works in two ways:
- Unknown queries are passed to your “upstream” DNS servers.
- i.e. The DNS servers you’re already using if you have no cache present.
- Queries that have been seen before are returned from the cache.
- Subject to the usual TTL values.
Installing pdnsd on Debian Systems
Installation is pretty simple, using the standard
# aptitude install pdnsd
Once installed you need to change the “
START_DAEMON=” setting to be “
/etc/default/pdnsd, at which point you can start the deamon:
# /etc/init.d/pdnsd start
Assuming that works you can test the software by performing a lookup, and timing it:
$ dig -t a example.com @127.0.0.1 | grep time ;; Query time: 29 msec
Repeating that lookup should show the second attempt took zero seconds:
$ dig -t a example.com @127.0.0.1 | grep time ;; Query time: 0 msec
If that second query was indeed “instant” then you can switch to using your caching DNS server by updating
/etc/resolv.conf to refer to it:
Author: Steve Kemp, of tweaked.io