Q. How do I set caching dns server to speed up dns lookup for my LAN (500 PC)? The DNS lookups creating a lot of network activity. There are a few times when this causes performance issues. How do I configure caching dns under Debian Linux?
A. Often many users and running daemon can perform tons of dns lookup. This can create problems for slow network connections as well the latency of the lookup can slow down overall experince for end users. For large sites / LANs / WANs it is recommended that you set your own caching dns servers.
dnsmasq dns caching serverdnsmasq is a lightweight DNS, TFTP and DHCP server. It is intended to provide coupled DNS and DHCP service to a LAN. Dnsmasq accepts DNS queries and either answers them from a small, local, cache or forwards them to a real, recursive, DNS server.
Step # 1: Install dnsmasqSimply, type the following command under Debian / Ubuntu Linux:
# apt-get install dnsmasq
Red Hat, Fedora / CentOS Linux user can grab dnsmasq rpm here or just enter:
# rpm -ivh http://dag.wieers.com/rpm/
Step # 2: Configure dnsmasqOpen /etc/resolv.conf
# vi /etc/resolv.conf
Set up upstream DNS servername i.e add ISP name server:
Save and close the file. Start dnsmasq dns caching server:
# /etc/init.d/dnsmasq start
Starting DNS forwarder and DHCP server: dnsmasqNow test your caching server:
$ dig openbsd.nixcraft.in
; <<>> DiG 9.4.1-P1 <<>> openbsd.nixcraft.in ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24426 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2 ;; QUESTION SECTION: ;openbsd.nixcraft.in. IN A ;; ANSWER SECTION: openbsd.nixcraft.in. 86341 IN A 18.104.22.168 ;; AUTHORITY SECTION: nixcraft.in. 51538 IN NS ns1.softlayer.com. nixcraft.in. 51538 IN NS ns2.softlayer.com. ;; ADDITIONAL SECTION: ns2.softlayer.com. 222764 IN A 22.214.171.124 ns1.softlayer.com. 220797 IN A 126.96.36.199 ;; Query time: 26 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Tue Jun 17 00:50:02 2008 ;; MSG SIZE rcvd: 134Try it one more time to see caching server in action:
$ dig openbsd.nixcraft.in
; <<>> DiG 9.4.1-P1 <<>> openbsd.nixcraft.in
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46610
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;openbsd.nixcraft.in. IN A
;; ANSWER SECTION:
openbsd.nixcraft.in. 86272 IN A 188.8.131.52
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Jun 17 00:51:11 2008
;; MSG SIZE rcvd: 53
Step # 3: Optional dnsmasq configurationThe default configuration file is located at /etc/dnsmasq.conf. By default it works out of box. However, configuration files offers more options. It is possible to use dnsmasq to block Web advertising by using a list of known banner-ad servers, all resolving to 127.0.0.1 or 0.0.0.0. It is also possible redirect local LAN mail traffic to central mail hub server. Please refer dnsmasq man pages for all advanced configuration options.
$ man dnsmasq