Replacing dnsmasq on OpenWRT

2013-10-30 11:34:11 +0000

Overview

My home router runs OpenWRT, which uses dnsmasq by default. However, I want to enable split-horizon DNS, so that different clients get different IP addresses for particular names.

This isn’t a feature of dnsmasq, so I need to install dhcpd and bind instead of dnsmasq.

Note: I have a guest WiFi network configured; this is the one that I’ll be messing around with, but it shouldn’t make any major difference to the following.

This is how I replaced dnsmasq; I’ll blog about configuring BIND’s DNS views later.

Connect using ssh

ssh openwrt-01

Removing dnsmasq

/etc/init.d/dnsmasq stop
opkg remove dnsmasq

Installing dhcpd

At the moment, I’m not running IPv6 – I’ll get to it at some point – so I chose to install the IPv4-only build of the ISC DHCP server:

opkg install isc-dhcp-server-ipv4

Configuring dhcpd

By default, dhcpd is configured to hand out addresses in the 192.168.1.1 range. This doesn’t coincide with any of my configured interfaces, which means that I get the error message:

No subnet declaration for br-lan (10.0.0.140).
** Ignoring requests on br-lan.  If this is not what
   you want, please write a subnet declaration
   in your dhcpd.conf file for the network segment
   to which interface br-lan is attached. **

No subnet declaration for wlan0-1 (192.168.58.1).
** Ignoring requests on wlan0-1.  If this is not what...


Not configured to listen on any interfaces!

To fix this, I edit /etc/dhcpd.conf, changing the 192.168.1.0 section appropriately.

I don’t want dhcpd answering requests on the br-lan interface; this is my internal network, and there’s a Windows Server already handling DHCP and DNS for that network.

Note that wlan0-1 is my guest WiFi interface; my internal WiFi interface is bridged to the br-lan interface.

Installing bind

The next step is to install BIND, to handle DNS lookups:

opkg install bind-server

Configuring bind – forwarders

At the very least, we need to configure BIND to forward requests it doesn’t understand to a normal DNS server.

Because this is my guest network, I’m going to use my ISPs name servers here, rather than my internal Windows DNS server.

To do this, edit the /etc/bind/named.conf file, and uncomment the forwarders section. Put your ISP’s name servers in here.

Configuring bind – authoritative domains

This is the point at which you’d configure BIND for the domains that you want it to be authoritative for.

For details, read the BIND documentation; it’s quite involved.

Cleaning up

Definitely:

rm /var/dhcp.leases         # dhcpd uses /var/dhcpd.leases, with a different format.

Optionally, but this might break LuCi:

rm /etc/config/dhcp
rm /var/etc/dnsmasq.conf    # automatically generated from /etc/config/dhcp