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doc:uci:dhcp [2012/10/30 18:33]
cjm add bogusnxdomain option
doc:uci:dhcp [2016/09/10 06:31] (current)
rseiler [Conditional DNS Forwarding for Windows Active Directory Domains / DNS Dependent Directory Based Authentication Services]
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 +====== DNS and DHCP configuration ======
  
 +The //dnsmasq// and dhcpd configuration is located in ''/​etc/​config/​dhcp''​ and controls both DNS and DHCP server options on the device (both DHCP and DNS services are implemented using the same OpenWrt program, dnsmasq).
 +
 +In the default configuration this file contains one //common section// to specify DNS and daemon related options and one or more //DHCP pools// to define DHCP serving on network interfaces.
 +
 +===== Sections =====
 +
 +Possible section types of the ''​dhcp''​ configuration file are defined below. Not all types may appear in the file and most of them are only needed for special configurations. The common ones are the //Common Options//, the //DHCP Pools// and //Static Leases//.
 +==== Common Options ====
 +
 +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 [[http://​www.thekelleys.org.uk/​dnsmasq/​docs/​dnsmasq-man.html|the dnsmasq man page]] for further details.
 +
 +These are the default settings for the common options:
 +
 +<​code>​config '​dnsmasq'​
 + option domainneeded 1
 + option boguspriv 1
 + option filterwin2k 0
 + option localise_queries 1
 + option rebind_protection 1
 + option rebind_localhost ​ 0
 + option local        '/​lan/'​
 + option domain  ​        '​lan'​
 + option expandhosts 1
 + option nonegcache 0
 + option authoritative 1
 + option readethers ​       1
 + option leasefile '/​tmp/​dhcp.leases'​
 + option resolvfile '/​tmp/​resolv.conf.auto'​
 +</​code>​
 +  * Options ''​local''​ and ''​domain''​ enable //dnsmasq// to serve entries in ''/​etc/​hosts''​ as well as the DHCP client'​s names as if they were entered into the //lan// DNS domain.
 +  * Options ''​domainneeded'',​ ''​boguspriv'',​ ''​localise_queries'',​ and ''​expandhosts''​ make sure that requests for these local host names (and the reverse lookup) never get forwarded to the upstream DNS servers.
 +  * Option ''​authoritative''​ makes the router the only DHCP server on this network; clients get their IP lease a lot faster this way.
 +  * Option ''​leasefile''​ stores the leases in a file, so that they can be picked up again if //dnsmasq// is restarted.
 +  * Option ''​resolvfile''​ tells //dnsmasq// to use this file to find upstream name servers; it gets created by the WAN DHCP client or the PPP client.
 +  * Options "​enable_tftp"​ and "​tftp_root"​ turn on the TFTP server and serve files from tftp_root. ​ You may need to set the server'​s IP on the client. ​ On the client, ​ change it by setting "​serverip"​ (e.g. "​setenv serverip 192.168.1.10"​).
 +
 +==== All Options ====
 +<​sortable>​
 +^ Name ^ Type ^ Default ^ Option ^ Description ^
 +| ''​add_local_domain''​ | boolean | ''​1''​ | | Add the local domain as search directive in resolv.conf. |
 +| ''​add_local_hostname''​ | boolean | ''​1''​ | | Add A and PTR records automatically for the local hostname. |
 +| ''​addnhosts''​ | list of file paths | //(none)// | ''​-H''​ | Additional host files to read for serving DNS responses |
 +| ''​authoritative''​ | boolean | ''​1''​ | ''​-K''​ | Force //dnsmasq// into authoritative mode. This speeds up DHCP leasing. Used if this is the only server on the network |
 +| ''​bogusnxdomain''​ | list of IP addresses | //(none)// | ''​-B''​ | IP addresses to convert into NXDOMAIN responses (to counteract "​helpful"​ upstream DNS servers that never return NXDOMAIN). |
 +| ''​boguspriv''​ | boolean | ''​0''​ | ''​-b''​ | Reject reverse lookups to private IP ranges where no corresponding entry exists in ''/​etc/​hosts''​ |
 +| ''​cachelocal''​ | boolean | ''​1''​ | | When set to ''​0'',​ use each network interface'​s ''​dns''​ address in the local ''/​etc/​resolv.conf''​. Normally, only the loopback address is used, and all queries go through //​dnsmasq//​. |
 +| ''​cachesize''​ | integer | ''​150''​ | ''​-c''​ | Size of //dnsmasq// query cache. |
 +| ''​dbus''​ | boolean | ''​0''​ | ''​-1''​ | Enable DBus messaging for //​dnsmasq//​.\\ :!: Standard builds of //dnsmasq// on OpenWRT do not include DBus support. |
 +| ''​dhcp_boot''​ | string | //(none)// |<​code>​--dhcp-boot</​code>​| Specifies BOOTP options, in most cases just the file name. You can also use: "''​file name'',​ ''​tftp server name'',​ ''​tftp ip address''"​|
 +| ''​dhcphostsfile''​ | file path | //(none)// | <​code>​--dhcp-hostsfile</​code>​ | Specify an external file with per host DHCP options |
 +| ''​dhcpleasemax''​ | integer | ''​150''​ | ''​-X''​ | Maximum number of DHCP leases |
 +| ''​dnsforwardmax''​ | integer | ''​150''​ | ''​-0''​ (zero) | Maximum number of concurrent connections |
 +| ''​domain''​ | domain name | //(none)// | ''​-s''​ | DNS domain handed out to DHCP clients |
 +| ''​domainneeded''​ | boolean | ''​1''​ | ''​-D''​ | Tells //dnsmasq// never to forward queries for plain names, without dots or domain parts, to upstream nameservers. If the name is not known from /etc/hosts or DHCP then a "not found" answer is returned |
 +| ''​dnssec''​ | boolean | ''​0''​ | <​code>​--dnssec</​code>​ | Validate DNS replies and cache DNSSEC data.\\ :!: Requires the //​dnsmasq-full//​ package. |
 +| ''​dnsseccheckunsigned''​ | boolean | ''​0''​ | <​code>​--dnssec-check-unsigned</​code>​ | Check the zones of unsigned replies to ensure that unsigned replies are allowed in those zones. This protects against an attacker forging unsigned replies for signed DNS zones, but is slower and requires that the nameservers upstream of //dnsmasq// are DNSSEC-capable.\\ :!: Requires the //​dnsmasq-full//​ package.\\ :!: Caution: If you use this option on a device that doesn'​t have a hardware clock, dns resolution may break after a reboot of the device due to an incorrect system time. |
 +| ''​ednspacket_max''​ | integer | ''​1280''​ | ''​-P''​ | Specify the largest EDNS.0 UDP packet which is supported by the DNS forwarder |
 +| ''​enable_tftp''​ | boolean | ''​0''​ | <​code>​--enable-tftp</​code>​ | Enable the builtin TFTP server |
 +| ''​expandhosts''​ | boolean | ''​1''​ | ''​-E''​ | Add the local domain part to names found in ''/​etc/​hosts''​ |
 +| ''​filterwin2k''​ | boolean | ''​0''​ | ''​-f''​ | Do not forward requests that cannot be answered by public name servers |
 +| ''​fqdn''​ | boolean | ''​0''​ | <​code>​--dhcp-fqdn</​code>​ | Do not resolve unqualifed local hostnames. Needs ''​domain''​ to be set. |
 +| ''​interface''​ | list of interface names | //(all interfaces)//​ | ''​-i''​ | List of interfaces to listen on. If unspecified,​ //dnsmasq// will listen to all interfaces except those listed in ''​notinterface''​. Note that //dnsmasq// listens on loopback by default. |
 +| ''​leasefile''​ | file path | //(none)// | ''​-l''​ (ell) | Store DHCP leases in this file |
 +| ''​local''​ | string | //(none)// | ''​-S''​ | Look up DNS entries for this domain from ''/​etc/​hosts''​. This follows the same syntax as ''​server''​ entries, see the man page. |
 +| ''​localise_queries''​ | boolean | ''​0''​ | ''​-y''​ | Choose IP address to match the incoming interface if multiple addresses are assigned to a host name in ''/​etc/​hosts''​. :!: Note well the spelling of this option. |
 +| ''​localservice''​ | boolean | ''​1''​ | <​code>​--local-service</​code>​ | Accept DNS queries only from hosts whose address is on a local subnet, ie a subnet for which an interface exists on the server. |
 +| ''​logqueries''​ | boolean | ''​0''​ | ''​-q''​ | Log the results of DNS queries, dump cache on SIGUSR1 |
 +| ''​nodaemon''​ | boolean | ''​0''​ | ''​-d''​ | Don't daemonize the //dnsmasq// process |
 +| ''​nohosts''​ | boolean | ''​0''​ | ''​-h''​ | Don't read DNS names from ''/​etc/​hosts''​ |
 +| ''​nonegcache''​ | boolean | ''​0''​ | ''​-N''​ | Disable caching of negative "no such domain"​ responses |
 +| ''​noresolv''​ | boolean | ''​0''​ | ''​-R''​ | Don't read upstream servers from ''/​etc/​resolv.conf''​ |
 +| ''​notinterface''​ | list of interface names |  //(none)// | ''​-I''​ (eye) | Interfaces //dnsmasq// should not listen on. |
 +| ''​nonwildcard''​ | boolean | ''​0''​ | ''​-z''​ | Bind only configured interface addresses, instead of the wildcard address. ​ |
 +| ''​port''​ | port number | ''​53''​ | ''​-p''​ | Listening port for DNS queries, disables DNS server functionality if set to ''​0''​ |
 +| ''​queryport''​ | integer | //(none)// | ''​-Q''​ | Use a fixed port for outbound DNS queries |
 +| ''​readethers''​ | boolean | ''​0''​ | ''​-Z''​ | Read static lease entries from ''/​etc/​ethers'',​ re-read on SIGHUP |
 +| ''​rebind_protection''​ | boolean | ''​1''​ | <​code>​--stop-dns-rebind</​code>​ | Enables DNS rebind attack protection by discarding upstream RFC1918 responses |
 +| ''​rebind_localhost''​ | boolean | ''​0''​ | <​code>​--rebind-localhost-ok</​code>​ | Allows upstream 127.0.0.0/8 responses, required for DNS based blacklist services, only takes effect if rebind protection is enabled |
 +| ''​rebind_domain''​ | list of domain names | //(none)// | <​code>​--rebind-domain-ok</​code>​ | List of domains to allow RFC1918 responses for, only takes effect if rebind protection is enabled |
 +| ''​resolvfile''​ | file path | ''/​etc/​resolv.conf''​ | ''​-r''​ | Specifies an alternative resolv file |
 +| ''​server''​ | list of strings | //(none)// | ''​-S''​ | List of DNS servers to forward requests to. See the //dnsmasq// man page for syntax details. |
 +| ''​strictorder''​ | boolean | ''​0''​ | ''​-o''​ | Obey order of DNS servers in ''/​etc/​resolv.conf''​ |
 +| ''​tftp_root''​ | directory path | //(none)// | <​code>​--tftp-root</​code>​ | Specifies the TFTP root directory |
 +</​sortable>​
 +
 +==== DHCP Pools ====
 +
 +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:
 +
 +<​code>​config '​dhcp'​ '​lan'​
 + option '​interface' ​  '​lan'​
 + option '​start' ​      '​100'​
 + option '​limit'​  ​    '​150'​
 + option '​leasetime' ​  '​12h'​
 +        option ra server
 +        option dhcpv6 server</​code>​
 +
 +  * ''​lan''​ specifies the OpenWrt interface that is served by this DHCP pool
 +  * ''​100''​ is the offset from the network address, in the default configuration this would mean start leasing addresses from ''​192.168.1.100''​
 +  * ''​150''​ is the maximum number of addresses that may be leased, in the default configuration this would mean leasing addresses up to ''​192.168.1.250''​
 +  * ''​12h''​ specifies the time to live for handed out leases, twelve hours in this example
 +  * ''​server''​ defines the mode for IPv6 configuration (RA & DHCPv6)
 +
 +Below is a listing of legal options for ''​dhcp''​ sections.
 +
 +<​sortable>​
 +^ Name ^ Type ^ Required ^ Default ^ Description ^
 +| ''​dhcp_option''​ | list of strings | no | //(none)// | The ID dhcp_option here must be with written with an underscore. OpenWrt will translate this to --dhcp-option,​ with a hyphen, as ultimately used by dnsmasq. Multiple option values can be given for this //​network-id//,​ with a a space between them and the total string between ""​. E.g. '​26,​1470'​ or '​option:​mtu,​ 1470' that can assign an MTU per DHCP. Your client must accept MTU by DHCP for this to work. Or "​3,​192.168.1.1 6,​192.168.1.1"​ to give out gateway and dns server addresses. |
 +| ''​dynamicdhcp''​ | boolean | no | ''​1''​ | Dynamically allocate client addresses, if set to ''​0''​ only clients present in the ''​ethers''​ files are served |
 +| ''​force''​ | boolean | no | ''​0''​ | Forces DHCP serving on the specified interface even if another DHCP server is detected on the same network segment |
 +| ''​ignore''​ | boolean | no | ''​0''​ | Specifies whether //dnsmasq// should ignore this pool if set to ''​1''​ |
 +| ''​dhcpv6''​ | string | no | ''​none''​ | Specifies whether DHCPv6 server should be enabled (''​server''​),​ relayed (''​relay''​) or disabled (''​disabled''​) |
 +| ''​ra''​ | string | no | ''​none''​ | Specifies whether Router Advertisements should be enabled (''​server''​),​ relayed (''​relay''​) or disabled (''​disabled''​) |
 +| ''​ndp''​ | string | no | ''​none''​ | Specifies whether NDP should be relayed ''​relay''​ or disabled ''​none''​ |
 +| ''​master''​ | boolean | no | 0 | Specifies whether DHCPv6, RA and NDP in relay mode is a master interface or not. |
 +| ''​interface''​ | logical interface name | yes | //(none)// | Specifies the interface associated with this DHCP address pool; must be one of the interfaces defined in ''/​etc/​config/​network''​.|
 +| ''​leasetime''​ | string | yes | ''​12h''​ | Specifies the lease time of addresses handed out to clients, for example ''​12h''​ or ''​30m''​ |
 +| ''​limit''​ | integer | yes | ''​150''​ | Specifies the size of the address pool (e.g. with start=100, limit=150, maximum address will be .249) |
 +| ''​networkid''​ | string | no | //(value of ''​interface''​)//​ | The dhcp functionality defined in the dhcp section is limited to the interface indicated here through its //​network-id//​. In case omitted the system tries to know the network-id via the '​interface'​ setting in this dhcp section, through consultation of /​etc/​config/​network. Some IDs get assigned dynamically,​ are not provided by network, but still can be set here.  |
 +| ''​start''​ | integer | yes | ''​100''​ | Specifies the offset from the network address of the underlying interface to calculate the minimum address that may be leased to clients. It may be greater than 255 to span subnets.|
 +</​sortable>​
 +
 +Notes:
 +  * Although called '​interface',​ this is the network name, i.e. lan, wan, wifi etc. (section names in /​etc/​config/​network),​ NOT the interface name used internally, like eth0, eth1, wlan0 etc. (the '​ifname'​ IDs in /​etc/​config/​network).
 +  * Although called '​networkid',​ this is the interface name used internally, i.e. eth0, eth1, wlan0 etc., not the network name (lan, wan, wifi etc.).
 +This departs from '​ifname'​ and '​network'​ as used in /​etc/​config/​network and in /​etc/​config/​wireless,​ so double check!
 +
 +==== Static Leases ====
 +
 +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//​.
 +
 +<​code>​config host
 +        option ip       '​192.168.1.2'​
 +        option mac      '​00:​11:​22:​33:​44:​55'​
 +        option name     '​mypc'​
 +</​code>​
 +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.
 +
 +<​code>​config host
 +        option ip       '​192.168.1.3'​
 +        option mac      '​11:​22:​33:​44:​55:​66 aa:​bb:​cc:​dd:​ee:​ff'​
 +        option name     '​mylaptop'​
 +</​code>​
 +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.
 +^ Name ^ Type ^ Required ^ Default ^ Description ^
 +| ''​ip''​ | string | yes | //(none)// | '​ignore'​ or the IP address to be used for this host. |
 +| ''​mac''​ | string | no | //(none)// | The hardware address(es) of this host, separated by commas. |
 +| ''​hostid''​ | string | no | //(none)// | The IPv6 interface identifier (address suffix) as hexadecimal number (max. 8 chars) |
 +| ''​duid''​ | string | no | //(none)// | The DHCPv6-DUID of this host. |
 +| ''​name''​ | string | no | //(none)// | Optional hostname to assign. |
 +| ''​tag''​ | string | no | //(none)// | Set the given tag for matching hosts. |
 +| ''​dns''​ | boolean | no | ''​0''​ | Add static forward and reverse DNS entries for this host. |
 +| ''​broadcast''​ | boolean | no | ''​0''​ | Force broadcast DHCP response. |
 +| ''​leasetime''​ | string | no | //(none)// | Host-specific lease time, e.g. 2m, 3h, 5d. Note: introduced by r48801 in trunk |
 +
 +As well as adding ''​host''​ sections, you can also enable the ''​dnsmasq''​ section option ''​readethers'',​ and add entries to the ''/​etc/​ethers''​ file.
 +
 +==== DHCP OPTION example to set an alternative default gateway ====
 +You can specify an alternative default Gateway
 +
 +<​code>​config '​dhcp'​ '​lan'​
 +        option '​interface'​ '​lan'​
 +        option '​start'​ '​100'​
 +        option '​limit'​ '​150'​
 +        option '​leasetime'​ '​12h'​
 +        list '​dhcp_option'​ '​3,​192.168.1.2'​
 +</​code>​
 +
 +use the list '​dhcp_option'​ '​3,​192.168.1.2'​ to set the default gateway. A list of options can be found here  [[http://​www.networksorcery.com/​enp/​protocol/​bootp/​options.htm | here]]
 +
 +==== Booting Options ====
 +
 +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.
 +
 +<​code>​config boot linux
 +        option filename ​        '/​tftpboot/​pxelinux.0'​
 +        option serveraddress ​   '​192.168.1.2'​
 +        option servername ​      '​fileserver'​
 +        list   ​dhcp_option ​     '​option:​root-path,​192.168.1.2:/​data/​netboot/​root'​
 +</​code>​
 +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.
 +<​sortable>​
 +^ Name ^ Type ^ Required ^ Default ^ Description ^
 +| ''​dhcp_option''​ | list of strings | no | //(none)// | Additional options to be added for this network-id. :!: If you specify this, you also need to specify the network-id. |
 +| ''​filename''​ | string | yes | //(none)// | The filename the host should request from the boot server. |
 +| ''​networkid''​ | string | no | //(none)// | The network-id these boot options should apply to. Applies to all clients if left unspecified. |
 +| ''​serveraddress''​ | string | yes | //(none)// | The IP address of the boot server. |
 +| ''​servername''​ | string | yes | //(none)// | The hostname of the boot server. |
 +| ''​force''​ | bool | no | //(none)// | dhcp-option will 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. |
 +</​sortable>​
 +
 +==== Classifying Clients And Assigning Individual Options ====
 +
 +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 OpenWrt, 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:
 +
 +''​config //​classifier//​
 +        option //​classifier// ​ '//​value//'​
 +        option networkid ​  '//​network-id//'​
 +        list   ​dhcp_option '//​DHCP-option//'​ ''​
 +
 +The placeholder ''//​classifier//''​ can be one of these values:
 +^ Classifier ^ Description ^
 +| ''​mac'' ​ | Hardware address of the client |
 +| ''​vendorclass'' ​ | String sent by the client representing the vendor of the client. //dnsmasq// performs a substring match on the vendor class string using this value. |
 +| ''​userclass'' ​ | String sent by the client representing the user of the client. //dnsmasq// performs a substring match on the user class string using this value. |
 +| ''​circuitid'' ​ | Matches the circuit ID as sent by the relay agent, as defined in RFC3046. |
 +| ''​remoteid'' ​ | Matches the remote ID as sent by the relay agent, as defined in RFC3046. |
 +| ''​subscrid'' ​ | Matches the subscriber ID as sent by the relay agent, as defined in RFC3993. |
 +
 +
 +An example using the '​mac'​ classifier to create a tagged network for openvpn would look like this in the config file:
 +<​code>​
 +config mac '​opnvpn'​
 +        option mac  '​00:​FF:​*:​*:​*:​*'​
 +        option networkid ​  '​opnvpn'​
 +        list   ​dhcp_option '​3'​
 +</​code>​
 +
 +
 +And like this in UCI
 +<​code>​
 +dhcp.opnvpn=mac
 +dhcp.opnvpn.mac=00:​FF:​*:​*:​*:​*
 +dhcp.opnvpn.networkid=opnvpn
 +dhcp.opnvpn.dhcp_option=3
 +</​code>​
 +
 +//​DHCP-option//​ adds a DHCP option for this //​network-id//​. See the //dnsmsq// 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.
 +
 +
 +===== Using plain dnsmasq.conf =====
 +
 +It is possible to mix the traditional ''/​etc/​dnsmasq.conf''​ configuration file with the options found in ''/​etc/​config/​dhcp''​.
 +
 +The ''​dnsmasq.conf''​ file does not exist by default but will be processed by //dnsmasq// on startup if it is present. Note that options in ''/​etc/​config/​dhcp''​ take precendence over ''​dnsmasq.conf''​ since they are translated to command line arguments.
 +
 +You can have ''​dnsmasq''​ execute a script on every action:
 +
 +<​code>​dhcp-script=/​sbin/​action.sh</​code>​
 +
 +==== DNS and DHCP Ports ====
 +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.
 +
 +===== Examples =====
 +
 +==== Static Lease (MAC address hot swap) ====
 +
 +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.
 +
 +<​code>​config '​host'​
 + option '​name'​ '​example-host'​
 + option '​ip' ​  '​192.168.1.230'​
 + option '​mac' ​ '​00:​a0:​24:​5a:​33:​69 00:​11:​22:​33:​44:​55'</​code>​
 +
 +=== Troubleshooting ===
 +:!: **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 [[http://​tools.ietf.org/​html/​rfc1531#​section-3.1|DORA]] loop.
 +
 +Solution:
 +  - Create a bridge from the wireless and ethernet interfaces on your client
 +    * it's trivial: [[googe>​windows 7 create bridge|google it]]
 +    * you will have to add the MAC address of the bridge to ''/​etc/​config/​dhcp''​
 +      * <​code>​config '​host'​
 + option '​name'​ '​example-host'​
 + option '​ip' ​  '​192.168.1.230'​
 + option '​mac' ​ '​00:​a0:​24:​5a:​33:​69 00:​11:​22:​33:​44:​55 02:​a0:​24:​5a:​33:​69 02:​11:​22:​33:​44:​55'</​code>​
 +    * Since the bridge will probably take and alter your ethernet MAC address, you will lose SLAAC on wifi interface, making your laptop IPv6-disabled when only wireless is up.
 +  - Another solution is IPv6 friendly, you don't need to create a bridge, nor add MAC address to dnsmasq config file, but it involves user interaction:​
 +    * When you plug the ethernet cable in, disable wireless interface in control panel (power off wireless won't do it). 
 +    * When you unplug ethernet cable, enable wireless and disable ethernet.
 +
 +Notes:
 +  * http://​answers.microsoft.com/​en-us/​windows/​forum/​windows_7-networking/​windows-7-refuses-dhcp-addresses-if-they-were/​1b72b289-0f58-492f-afb8-e76c80a81f00
 +  * //force// is a bool option that will force 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.
 +==== Only allow static leases ====
 +
 +If you want to distribute IPv4 addresses to known clients only (static leases), use:
 +
 +<​code>​
 +config dhcp '​lan'​
 +        ...
 +        option dynamicdhcp 0
 +</​code>​
 +
 +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.
 +
 +==== Custom Domain ====
 +
 +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.
 +
 +:!: Note that this currently only works for IPv4 addresses and that this functionality is not present in release prior to 8.09.2 .
 +
 +:!: Note that reverse records are not properly generated at present. (Barrier Breaker 14.07-RC2)
 +
 +<​code>​config '​domain'​
 + option '​name'​ '​typhoon'​
 + option '​ip' ​  '​192.168.1.140'</​code>​
 +
 +
 +another example: redirect www.facebook.com
 +<​file>​
 +config '​domain'​
 + option '​name'​ '​www.facebook.com'​
 + option '​ip' ​  '​1.2.3.4'​
 +        #the request to www.facebook.com will end to 1.2.3.4
 +</​file>​
 +==== SRV RR for SIP ====
 +
 +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:
 +
 +<​code>​config '​srvhost'​
 + option srv  '​_sip._udp.mydomain.com'​
 + option target '​pbx.mydomain.com'​
 + option port 5060
 + option class 0
 + option weight 10</​code>​
 +
 +==== CNAME RR ====
 +
 +A Canonical Name record specifes 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:
 +
 +<​code>​config '​cname'​
 + option cname '​ftp.example.com'​
 + option target '​www.example.com'</​code>​
 +Note that it is necessary to use fully qualified domain names.
 +==== MX RR ====
 +
 +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:
 +
 +<​code>​config '​mxhost'​
 + option domain '​yyy.zzz'​
 + option relay '​my.host.com'​
 + option pref 10</​code>​
 +
 +will mitigate the issues caused by split-horizon.
 +
 +==== TFTP Boot ====
 +
 +Direct BOOTP requests to the TFTP server at the IP address ''​192.168.1.2''​ and use ''/​tftpboot/​pxelinux.0''​ as boot file name.
 +
 +<​code>​config '​boot'​
 + option '​filename' ​     '​pxelinux.0'​
 + option '​servername' ​   '​data'​
 + option '​serveraddress'​ '​192.168.1.2'</​code>​
 +
 +==== Multiple DHCP options ====
 +
 +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.
 +
 +<​code>​config '​dhcp'​ '​lan'​
 +        option '​interface'​ '​lan'​
 +        option '​start'​ '​62'​
 +        option '​limit'​ '​192'​
 +        option '​leasetime'​ '​600h'​
 +        list '​dhcp_option'​ '​66,​172.16.60.64'​
 +        list '​dhcp_option'​ '​150,​172.16.60.64'</​code>​
 +
 +==== Multiple DHCP/DNS server/​forwarder instances ====
 +
 +If you need multiple DNS forwarders with different configurations or DHCP server with different sets of lease files,
 +have a look at this [[https://​dev.openwrt.org/​ticket/​8862|patch]].
 +Multiple dnsmasq "​named"​ instances can be configured:
 +<​code>​config '​dnsmasq'​ '​hotspot'​
 +        option nonwildcard '​1'​ # Tell dnsmasq to bind specific address(es)
 +        option resolvfile '/​tmp/​resolv.conf.hotspot'​
 +        ...
 +</​code>​
 +
 +Your configs are usally active for all instances, but you can limit them to single instances by:
 +<​code>​config '​dhcp'​ '​lan'​
 +        option '​interface'​ '​lan'​
 +        option '​dnsmasq_config'​ '​hotspot'​
 +
 +config '​host'​
 +        option '​name'​ '​chef'​
 +        option '​mac'​ '​00:​00:​00:​00:​00:​00'​
 +        option '​ip'​ '​192.168.1.66'​
 +        option '​dnsmasq_config'​ '​hotspot'​
 +</​code>​
 +
 +The web interface (luci) has not been updated for this patch yet.
 +
 +==== Assigning DHCP pool to a subnet in a large network ====
 +
 +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
 +
 +<​code>​
 +config dhcp lan
 +  option interface lan
 +  option start 1441793
 +  option limit 253
 +</​code>​
 +Test:
 +<​code>​
 +root@OpenWrt:​~#​ ipcalc.sh 10.0.0.1 255.0.0.0 1441793 253
 +IP=10.0.0.1
 +NETMASK=255.0.0.0
 +BROADCAST=10.255.255.255
 +NETWORK=10.0.0.0
 +PREFIX=8
 +START=10.22.0.1
 +END=10.22.0.254
 +root@OpenWrt:​~#​
 +</​code>​
 +
 +==== Classifying Clients And Assigning Individual Options ====
 +
 +Assign different dhcp-options to a single MAC address:
 +<code bash>
 +uci batch <<'​EOF'​
 +add dhcp mac
 +set dhcp.@mac[-1].mac=00:​11:​22:​33:​44:​55
 +set dhcp.@mac[-1].networkid=someone
 +add_list dhcp.@mac[-1].dhcp_option=6,​192.168.1.3,​192.168.1.2,​192.168.1.1
 +add_list dhcp.@mac[-1].dhcp_option=3,​192.168.1.2
 +add_list dhcp.@mac[-1].dhcp_option=44,​192.168.1.3
 +commit dhcp
 +EOF
 +uci commit dhcp
 +/​etc/​init.d/​dnsmasq reload
 +</​code>​
 +Where 6=DNS, 3=Default Gateway, 44=WINS
 +
 +Assign different dhcp-options to multiple hosts:
 +
 +<code bash>
 +config host
 +    option name '​j400'​
 +    option mac '​00:​21:​63:​75:​aa:​17'​
 +    option ip '​10.11.12.14'​
 +    option tag '​vpn' ​ # assign tag "​vpn"​ to this host
 +
 +config host
 +    option name '​j500'​
 +    option mac '​01:​22:​64:​76:​bb:​18'​
 +    option ip '​10.11.12.15'​
 +    option tag '​vpn' ​ # assign tag "​vpn"​ to this host
 +
 +config tag '​vpn' ​ # match tag "​vpn"​
 +    list dhcp_option '​6,​8.8.8.8,​8.8.4.4' ​ # assign arbritary extra dhcp options to this tag
 +    option force '​1' ​             #​dhcp-option will 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.
 +</​code>​
 +
 +:!: Generally, specifying a dhcp option without any value, would disable that option. so for example you can use:
 +<​code>​list dhcp_option '​3'</​code>​
 +to disable sending a default gateway to a specific client
 +
 +FIXME Convert to procd: etc/​init.d/​dnsmasq restart ​
 +==== Enabling DHCP without enabling DNS ====
 +
 +This is useful when you just want to hand out addresses to clients, without doing any DNS.
 +
 +<​code>​
 +config dnsmasq
 +       ...
 +       ​option port 0
 +       ​option domain ''​
 +</​code>​
 +
 +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:
 +
 +<​code>​
 +config dhcp lan
 +       ​option interface lan
 +       ...
 +       list dhcp_option "​6,​80.67.188.188,​6,​80.67.169.12"​
 +       list dns         "​2001:​913::​8"​
 +       list dns         "​2001:​910:​800::​12" ​      
 +</​code>​
 +
 +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.
 +
 +==== Enabling DNS without enabling DHCP ====
 +
 +dnsmasq can be used to provide clients with a DNS server but not with DHCP (for example, if DHCP is already supplied by a separate server).
 +
 +First, dnsmasq must be turned on for the internal interface:
 +
 +  * Network > Interfaces
 +    * click the desired internal interface to select it
 +      * DHCP Server
 +        * click the "Setup DHCP Server"​ button to enable dnsmasq on this interface -- this will enable both DHCP and DNS
 +
 +Now that dnsmasq is enabled, the DHCP portion of dnsmasq needs to be turned off.
 +
 +  * Network > Interfaces
 +    * click the desired internal interface to select it
 +      * DHCP Server
 +        * Ignore interface: Enable this option
 +      * Save & Apply
 +
 +This change will turn off just DHCP but leave DNS services available on the specified interface.
 +
 +==== Several DNS servers ====
 +<​file>​
 +config dnsmasq
 +        option domainneeded '​1'​
 +        option localise_queries '​1'​
 +        option local '/​lan/'​
 +        option domain '​lan'​
 +        option expandhosts '​1'​
 +        option authoritative '​1'​
 +        option readethers '​1'​
 +        option leasefile '/​tmp/​dhcp.leases'​
 +        option resolvfile '/​tmp/​resolv.conf.auto'​
 +        list server '/​subdomain.example.com/​192.0.2.1'​
 +          #be careful that some options should be absent (or set to False)
 +          #to allow the forwarding towards the "so defined"​ private networks
 +          #​http://​en.wikipedia.org/​wiki/​Private_network
 +          # likely '​bogusprivat'​
 +        list server '/​example.com/​208.67.222.222'​
 +        option rebind_protection '​0'​
 +</​file>​
 +
 +
 +
 +==== Conditional DNS Forwarding for Windows Active Directory Domains / DNS Dependent Directory Based Authentication Services ====
 +
 +1. Install dnsmasq using your local package manager
 +
 +2. Edit **/​etc/​dnsmasq.conf**
 +
 +# Tells dnsmasq to forward anything with the domain of remote.local to dns (example) server 10.25.11.2:​\\
 +**server=/​remote.local/​10.25.11.2**
 +
 +# Listen to requests only coming from the local machine:\\
 +**listen-address=127.0.0.1**
 +
 +# Do not cache anything
 +# A decent dns server will already cache for your local network:\\
 +**cache-size=0**
 +
 +3. Edit **/​etc/​resolv.conf**
 +
 +# Local LAN Domain:\\
 +**domain ion.lan**
 +
 +# local dnsmasq server:\\
 +**nameserver 127.0.0.1**
 +
 +# Your main dns server (dnsmasq will forward all requests to this example server):\\
 +**nameserver 10.20.1.1**
 +
 +4. Start dnsmasq
 +
 +5. Test – ping a local server and remote server using the FQDN
 +
 +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: ​ [[http://​pyther.net/​2010/​12/​dns-conditional-forwarding-dnsmasq/​]]
 +
 +<​code>​
 +
 +cat /​etc/​config/​dhcp ​
 +
 +config dnsmasq
 +        option localise_queries '​1'​
 +        option rebind_protection '​0'​
 +        option authoritative '​1'​
 +        option leasefile '/​tmp/​dhcp.leases'​
 +        option localservice '​1'​
 +        option dnssec '​0'​
 +        option cachesize '​0'​
 +        option domain '​example.local'​
 +        option readethers '​1'​
 +        option logqueries '​1'​
 +        option fliterwin2k '​0'​
 +        #Define your Domain and Domain Controllers IP address here.       
 +        option local '/​example.local/​192.168.1.X'​**
 +        list server '/​0.openwrt.pool.ntp.org/​8.8.8.8'​
 +        list server '/​1.openwrt.pool.ntp.org/​8.8.8.8'​
 +        list server '/​2.openwrt.pool.ntp.org/​8.8.8.8'​
 +        list server '/​3.openwrt.pool.ntp.org/​8.8.8.8'​
 +        option resolvfile '/​etc/​resolv.conf'​
 +        option boguspriv '​1'​
 +
 +config dhcp '​lan'​
 +        option interface '​lan'​
 +        option start '​100'​
 +        option limit '​150'​
 +        option leasetime '​12h'​
 +</​code>​
 +Almost completed, Now on to the finalization 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. 
 +
 +<​code>​
 +rm /​etc/​resolv.conf
 +echo "​domain example.local">>/​etc/​resolv.conf
 +echo "​nameserver 127.0.0.1">>/​etc/​resolv.conf
 +echo "​nameserver 208.67.220.220">>/​etc/​resolv.conf
 +
 +</​code>​
 +
 +<​code>​
 +
 + cat /​etc/​resolv.conf
 +#Define your Domain Below  & Public DNS you desire. ​
 +
 +domain example.local
 +nameserver 127.0.0.1
 +nameserver 208.67.220.220
 +
 +</​code>​
 +
 +===== Troubleshooting =====
 +==== Losing connection due to missing dhcp response when the network is overloaded ====
 +Sometimes when an interface is on the edge of the capacity ​
 +(especially wifi over longer distances) a dhcp request could
 +be not replied in time and therefore the dhcp client will not be
 +able to receive proper network settings. A possible workaround is using static
 +IPs or very long dhcp leases (more than 12h). This is particularly important
 +when one has several wifi repeaters that use dhcp and are distant from each other or not easily
 +accessible.