Unbound – domains cached only for short time

domain-name-systemlinuxmintunbound

I recently set up Unbound for DNS caching, along with DNScrypt on Linux Mint 18.1. It works, but I noticed the pages are cached only for short time:

  1. First query to google.com – 48ms (domain not cached)
  2. Second query to google.com (immediately after that) – 0ms (domain cached)
  3. Third query to google.com (after ~ minute) – 46ms (domain not cached)

Is this intended behavior, or do I need to set something different to cache pages for longer time? Here is my Unbound config (/etc/unbound/unbound.conf):
#

 Unbound configuration file for Debian.
    #
    # See the unbound.conf(5) man page.
    #
    # See /usr/share/doc/unbound/examples/unbound.conf for a commented
    # reference config file.age
    #
    # The following line includes additional configuration files from the
    # /etc/unbound/unbound.conf.d directory.
    include: "/etc/unbound/unbound.conf.d/*.conf"
    server:
        verbosity: 1
        num-threads: 4
        outgoing-range: 8192
        so-rcvbuf: 4m
        so-sndbuf: 4m
        so-reuseport: yes
        msg-cache-size: 50m
        msg-cache-slabs: 16
        num-queries-per-thread: 4096
        rrset-cache-size: 100m
        rrset-cache-slabs: 16
        infra-cache-slabs: 16
        do-ip4: yes
        do-ip6: no
        do-udp: yes
        do-tcp: yes
        do-daemonize: yes
        hide-identity: yes
        hide-version: yes 
        harden-short-bufsize: yes
        harden-large-queries: yes
        harden-glue: yes
        harden-dnssec-stripped: yes
        harden-below-nxdomain: yes
        harden-referral-path: yes
        logfile: "/etc/unbound/unbound.log"
        use-caps-for-id: yes
        do-not-query-localhost: no
        prefetch: no 
    forward-zone:
        name: "."
        forward-addr: 127.0.0.1@40

Best Answer

Unbound will (or at least should) be caching the result for the time specified in the TTL for the record you are requesting.

This is exactly what I observe on a system I have to hand that is running unbound. The initial request takes 14ms, subsequent requests take 0ms and when the TTL expires the next request takes 14ms.

Initial request which shows a 300 second TTL and takes 18ms

;; ANSWER SECTION:
google.com.             300     IN      A       172.217.20.46

;; Query time: 18 msec
;; SERVER: 10.34.20.1#53(10.34.20.1)
;; WHEN: Sun Feb 12 20:39:30 2017
;; MSG SIZE  rcvd: 44

Subsequent requests - TTL is counting down and takes 0ms

;; ANSWER SECTION:
google.com.             196     IN      A       172.217.20.46

;; Query time: 0 msec
;; SERVER: 10.34.20.1#53(10.34.20.1)
;; WHEN: Sun Feb 12 20:41:14 2017
;; MSG SIZE  rcvd: 44

TTL expired so another upstream request is made 23ms

;; ANSWER SECTION:
google.com.             300     IN      A       172.217.20.46

;; Query time: 23 msec
;; SERVER: 10.34.20.1#53(10.34.20.1)
;; WHEN: Sun Feb 12 20:44:37 2017
;; MSG SIZE  rcvd: 44
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