Simple way to set up Split DNS

Tom Eastep

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Table of Contents

What is Split DNS
Why would I want to use Split DNS?
Setting up Split DNS

What is Split DNS

Split DNS is simply a configuration in which the IP address to which a DNS name resolves is dependent on the location of the client. It is most often used in a NAT environment to insure that local clients resolve the DNS names of local servers to their RFC 1918 addresses while external clients resolve the same server names to their public counterparts.

Why would I want to use Split DNS?

See Shorewall FAQ 2.

Setting up Split DNS

Setting up Split DNS is extremely simple:

  1. Be sure that your firewall/router can resolve external DNS names.

  2. Install the dnsmasq package ( and arrange for it to start at boot time. There are many dnsmasq HOWTOs on the Internet.

  3. Add your local hosts to /etc/hosts on the firewall/router using their local RFC 1918 addresses. Here's an example:

    # hosts         This file describes a number of hostname-to-address
    #               mappings for the TCP/IP subsystem.  It is mostly
    #               used at boot time, when no name servers are running.
    #               On small systems, this file can be used instead of a
    #               "named" name server.
    # Syntax:
    # IP-Address  Full-Qualified-Hostname  Short-Hostname
    #       localhost
    # special IPv6 addresses
    ::1             localhost ipv6-localhost ipv6-loopback
    fe00::0         ipv6-localneta
    ff00::0         ipv6-mcastprefix
    ff02::1         ipv6-allnodes
    ff02::2         ipv6-allrouters
    ff02::3         ipv6-allhosts ursa     linksys    opensuse      debian      ubuntu      fedora  opensuse11      centos    debian32     fedora9       blarg
  4. Configure your local network hosts to use the firewall/router as their DNS server. If your local hosts are configured using DHCP, that is a simple one-line change to the DHCP configuration.

And that's it! Your local clients will resolve those names in the firewall/router's /etc/hosts file as defined in that file. All other names will be resolved using the firewall/router's Name Server as defined in /etc/resolv.conf.


From an Internet Host:

gateway:~ # host has address
gateway:~ # 

From ubuntu (

teastep@ubuntu:~$ host linksys has address