Setting up a local DNS server with Unbound
Cache Configuration
For most home users, the best reason for using a local DNS server is caching DNS entries and speeding up web browsing. Listing 8 shows an example configuration for a simple, yet powerful, DNS cache.
Listing 8
cache_options.conf
# /etc/unbound/unbound.conf.d/cache_options.conf prefetch: yes # Fetch things before they expire from cache. prefetch-key: yes # Fetch DNSSEC keys early in the validation process. cache-min-ttl: 1200 # Seconds it takes for items in cache to die at minimum.
Domain names have an official time to live assigned by the manager of that domain. This time to live is the time that recursive DNS servers are supposed to keep the DNS entries in their caches before deleting them. Imagine that your Unbound server resolved richard-falken.com
, which at the time of this writing has a TTL of 86400 seconds. It would remember the DNS entry for richard-falken.com
for 24 hours.
Some domains have very short TTLs. The cache-min-ttl
directive in the example defines the minimum time a cached DNS entry will be allowed to live in the cache. If Unbound comes across a domain with a TTL shorter than 1200 seconds, the official TTL will be ignored, and 1200 seconds will be used instead. Beware that DNS entries that are conserved in the cache for too long may become stalled and outdated, which could be counterproductive and lead to problems. Use this directive wisely.
prefetch-key
instructs Unbound to fetch DNSSEC keys earlier than usual in the DNSSEC validation process. It saves time at the expense of CPU load.
prefetch
instructs the server to try to resolve cached entries that are about to expire from the cache in order to keep the cache fresh. This option might increase bandwidth consumption by about 10 percent, but response times will be better.
Privacy
Listing 9 has some privacy options. The most important is qname-minimisation
. Enabling this option makes the queries sent by Unbound to other DNS servers more compact and less prone to leak private information.
Listing 9
privacy_options.conf
# /etc/unbound/unbound.conf.d/privacy_options.conf hide-identity: yes # If enabled id.server and hostname.bind queries are refused. hide-version: yes # If enabled version.server and version.bind queries are refused. qname-minimisation: yes # Send minimum amount of information to upstream servers to enhance privacy.
hide-identity
and hide-version
are less relevant in LAN scenarios, since they prevent the DNS server from replying to internal special queries that attempt to obtain information, such as the hostname of the server or the software version.
Query Times
You may want to check the query times for a server provided by your ISP, another open DNS server on the Internet, or any server you configure on your own LAN.
Proper DNS benchmarking is difficult. A quick and dirty way to check the connection latency for a DNS server is using icmp echo
requests with the ping utility:
$ ping -c 4 $address_of_server
The time stat for each reply indicates the time it took to get a "pong" response from the server. The bigger the time, the longer it takes for the server to reply to you when you ask it to.
The dig utility (Figure 3) performs name resolution, and it is very useful for retrieving DNS records and checking query times.
$ dig @$address_of_dns_server example.org
If you are serious about benchmarking a DNS server, you will need heavier tools for the job. Google's namebench [11] is a popular option.
« Previous 1 2 3 4 Next »
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Direct Download
Read full article as PDF:
Price $2.95
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Find SysAdmin Jobs
News
-
Kubuntu Focus Announces XE Gen 2 Linux Laptop
Another Kubuntu-based laptop has arrived to be your next ultra-portable powerhouse with a Linux heart.
-
MNT Seeks Financial Backing for New Seven-Inch Linux Laptop
MNT Pocket Reform is a tiny laptop that is modular, upgradable, recyclable, reusable, and ships with Debian Linux.
-
Ubuntu Flatpak Remix Adds Flatpak Support Preinstalled
If you're looking for a version of Ubuntu that includes Flatpak support out of the box, there's one clear option.
-
Gnome 44 Release Candidate Now Available
The Gnome 44 release candidate has officially arrived and adds a few changes into the mix.
-
Flathub Vying to Become the Standard Linux App Store
If the Flathub team has any say in the matter, their product will become the default tool for installing Linux apps in 2023.
-
Debian 12 to Ship with KDE Plasma 5.27
The Debian development team has shifted to the latest version of KDE for their testing branch.
-
Planet Computers Launches ARM-based Linux Desktop PCs
The firm that originally released a line of mobile keyboards has taken a different direction and has developed a new line of out-of-the-box mini Linux desktop computers.
-
Ubuntu No Longer Shipping with Flatpak
In a move that probably won’t come as a shock to many, Ubuntu and all of its official spins will no longer ship with Flatpak installed.
-
openSUSE Leap 15.5 Beta Now Available
The final version of the Leap 15 series of openSUSE is available for beta testing and offers only new software versions.
-
Linux Kernel 6.2 Released with New Hardware Support
Find out what's new in the most recent release from Linus Torvalds and the Linux kernel team.