The config section type dnsmasq determines values and options relevant to the overall operation of dnsmasq and the DHCP options on all interfaces served. The following table lists all available options, their default value, as well as the corresponding dnsmasq command line option. See the dnsmasq man page for further details.

These are the default settings for the common options:

Sections of the type dhcp specify per interface lease pools and settings for serving DHCP requests. Typically there is at least one section of this type present in the /etc/config/dhcp file to cover the lan interface.

You can disable a lease pool for a specific interface by specifying the ignore option in the corresponding section.

A minimal example of a dhcp section is listed below:

Below is a listing of legal options for dhcp sections.

Notes:

You can assign fixed IP addresses to hosts on your network, based on their MAC (hardware) address.

The configuration options in this section are used to construct a -G option for dnsmasq.

This adds the fixed IP address 192.168.1.2 and the name "mypc" for a machine with the (Ethernet) hardware address 00:11:22:33:44:55.

This adds the fixed IP address 192.168.1.3 and the name "mylaptop" for a machine with the (Ethernet) hardware address 11:22:33:44:55:66 or aa:bb:cc:dd:ee:ff. Note that this is unreliable if more than one of the listed mac addresses is on the network simultaneously. It’s useful for cases such as a laptop with both wireless and wired interfaces, provided that only one will be active at a given time.

As well as adding host sections, you can also enable the dnsmasq section option readethers, and add entries to the /etc/ethers file.

You can specify an alternative default Gateway

use the list dhcp_option 3,192.168.1.2 to set the default gateway. A list of options can be found here here

Some hosts support booting over the network (PXE booting). DHCP/BOOTP is used to tell the host which file to boot and the server to load it from. Each client can only receive one set of filename and server address options. If different hosts should boot different files, or boot from different servers, you can use network-ids to map options to each client.

Usually, you need to set additional DHCP options (through dhcp_option) for further stages of the boot process. See the dnsmasq man page for details on the syntax of the O option.

The configuration options in this section are used to construct a -M option for dnsmasq.

Note: odhcp currently lacks support root-path specification. If you need this functionality, disable odhcpd and use dnsmasq instead.

This tells the client to load pxelinux.0 from the server at 192.168.1.2, and mount root from /data/netboot/root on the same server.

DHCP can provide the client with numerous options, such as the domain name, NTP servers, network booting options, etc. While some settings are applicable to all hosts in a network segment, other are more specific and apply only to a group of hosts, or even only a single one. dnsmasq offers to group DHCP options and their values by a network-id, an alphanumeric identifier, and sending options only to hosts which have been tagged with that network-id.

In LEDE, you can tag hosts by the DHCP range they’re in (section dhcp), or a number of options the client might send with their DHCP request. In each of these sections, you can use the dhcp_option list to add DHCP options to be sent to hosts with this network-id.

Each classifying section has two configuration options: the value of the DHCP option used to distinguish clients, and the network-id that these clients should be tagged with. Here’s a template:

The placeholder classifier can be one of these values:

An example using the mac classifier to create a tagged network for openvpn would look like this in the config file:

And like this in UCI

DHCP-option adds a DHCP option for this network-id. See the dnsmasq man page for a complete explanation of the syntax of the -O option.

force is a bool option. It forces dhcp-option to always be sent, even if the client does not ask for it in the parameter request list. This is sometimes needed, for example when sending options to PXELinux.

DNS needs TCP and UDP port 53 open on the firewall. DHCP needs UDP ports 67 and 68 open from your zone to/from the firewall. See http://wiki.openwrt.org/doc/recipes/guest-wlan and http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html (viz "--dhcp-alternate-port") for more information.

Define a static lease for a host with MAC addresses 00:a0:24:5a:33:69 and 00:11:22:33:44:55 (handy when you use both wired and wireless connection on the same computer/laptop - of course, you can use just one MAC address) and assign the IP address 192.168.1.230 and the hostname example-host to it. We call this MAC address hot swap, since IP address stay same, but MAC address changes.

CAUTION: Windows 7 has introduced a new Microsoft-enhanced feature. It won’t assign IP address obtained from a DHCP server to an interface, if the IP was used before for another interface, even if that other interface is NOT active currently (i.e. cable disconnected). This behaviour is unique and was not reported for older Windows versions, Mac OS nor Linux.

If you try configure MAC address hot swap on your router, Windows 7 clients will end up in an infinite DORA loop.

Solution: - Create a bridge from the wireless and ethernet interfaces on your client

Notes:

If you want to distribute IPv4 addresses to known clients only (static leases), use:

With this, dnsmasq will consider static leases defined in "config host" blocks and in /etc/ethers, and refuse to hand out any IPv4 address to unknown clients.

Note that you shouldn’t use this as a security feature to prevent unwanted clients from connecting. A client can simply configure a static IP in the right range to have access to the network.

Define a custom domain name and the corresponding PTR record - assigns the IP address 192.168.1.140 to the domain name typhoon and construct an appropriate reverse record 140.1.168.192.in-addr.arpa. It works like an entry in /etc/hosts but more flexible and integrated.

another example: redirect www.example.com to 1.2.3.4

To define an SRV record for SIP over UDP, with the default port of 5060 on the host pbx.mydomain.com, with a class of 0 and a weight of 10 one would use:

A Canonical Name record specifies that a domain name is an alias for another domain, the "canonical" domain. To specify that the web server also doubles as the FTP server, one might use:

Note that it is necessary to use fully qualified domain names.

If you’re running the mail server for your domain behind a firewall (and therefore, with split-horizon for your own domain) then you might need to convince that mailer that it’s actually authoritative for your domain.

If sendmail tells you "Domain of sender address xxx@yyy.zzz does not exist" this is because it isn’t finding an MX record confirming that it’s an MX relay for that domain.

Adding:

will mitigate the issues caused by split-horizon.

Direct BOOTP requests to the TFTP server at the IP address 192.168.1.2 and use /tftpboot/pxelinux.0 as boot file name.

Multiple DHCP options can be configured under a single dhcp_option object. In this case, option 66 (tftp-server) and option 150 (multiple tftp servers) were used for a Cisco Callmanager deployment.

If you need multiple DNS forwarders with different configurations or DHCP server with different sets of lease files, have a look at this patch. Multiple dnsmasq "named" instances can be configured:

Your configs are usually active for all instances, but you can limit them to single instances by:

The web interface (luci) has not been updated for this patch yet.

In DHCP pool limit setting, the start and limit values do not refer to the "last digit", they’re relative offsets to the network address. * the network address of 10.0.0.1 / 255.0.0.0 is 10.0.0.0 * the 10.22.0.1 start address is 22 x /16 subnets away: (2^16) * 22 = 1441792 * 10.0.0.0 + 1441792 + 1 = 10.22.0.1 → start = 1441793 * 10.22.0.254 - 10.22.0.1 = 253 → limit = 253

Test:

Assign different dhcp-options to a single MAC address:

Where 6=DNS, 3=Default Gateway, 44=WINS

Assign different dhcp-options to multiple hosts:

CAUTION: Specifying a dhcp option without any value, would disable that option. so for example you can use:

to disable sending a default gateway to a specific client

This is useful when you just want to hand out addresses to clients, without doing any DNS.

The second option prevents dnsmasq from giving out a domain name and DNS search list to clients: this is useless without DNS resolving.

Of course, you will want to hand out the address of a DNS resolver to clients:

The dhcp_option entry is meant for dnsmasq, while the more elegant dns entries are understood by odhcpd. By default, odhcpd is only used for IPv6, but if you also use odhcpd for IPv4, you can just use dns entries for everything.

All dns requests will be forwarded to 10.20.1.1 except any matching *.remote.local. server.remote.local will be forwarded to 10.25.11.2

Credit: here

Almost completed, Now on to the finalisation of the /etc/resolv.conf Traditionally /etc/resolv.conf is populated via symlink based on interface settings which get inserted via script into /tmp/resolv.conf. We’re going to disable this symlink because without doing so it would override our static settings.

You’ll want to remove /etc/resolv.conf That will remove the resolv.conf symlink. Then we will add the ip address of the secondary DNS and external resolving address inside the /etc/resolv.conf file finally establishing conditional forwarding, something that should be specified for easy configuration via the GUI.