This translation is older than the original page and might be outdated. See what has changed.

FIXME 本页面未完整翻译。请帮助完成翻译。
(一旦移除本段,表示翻译已经完成)

DHCP

DHCP配置文件位于 /etc/config/dhcp ,文件包含了DNS和DHCP服务的配置信息(DHCP和DNS服务都是通过 dnsmasq 实现的)。

在默认配置中,该文件包含一个 公共部分 来指定DNS和守护进程相关的选项以及一个或多个 DHCP池 ,以定义在网络接口上服务的DHCP。

下面定义了“DHCP”配置文件可能存在的节点类型。可能并非所有类型都出现在文件中,实际上,很多类型只适用于特殊配置。常见的节点类型有 普通选项DHCP池静态租赁

dnsmasq 类型的节点包含了全局设置相关的键值,该设置生效于所有dnsmasq实例。下表列出了所有可用键值、各键的默认值以及其相应的 dnsmasq 命令行样式。详情见dnsmasq手册页

这些是常用选项的默认设置:

root@lede:/# uci show dhcp
dhcp.@dnsmasq[0]=dnsmasq
dhcp.@dnsmasq[0].domainneeded='1'
dhcp.@dnsmasq[0].boguspriv='1'
dhcp.@dnsmasq[0].filterwin2k='0'
dhcp.@dnsmasq[0].localise_queries='1'
dhcp.@dnsmasq[0].rebind_protection='1'
dhcp.@dnsmasq[0].rebind_localhost='1'
dhcp.@dnsmasq[0].local='/lan/'
dhcp.@dnsmasq[0].domain='lan'
dhcp.@dnsmasq[0].expandhosts='1'
dhcp.@dnsmasq[0].nonegcache='0'
dhcp.@dnsmasq[0].authoritative='1'
dhcp.@dnsmasq[0].readethers='1'
dhcp.@dnsmasq[0].leasefile='/tmp/dhcp.leases'
dhcp.@dnsmasq[0].resolvfile='/tmp/resolv.conf.auto'
dhcp.@dnsmasq[0].localservice='1'
...
root@lede:/# cat /etc/config/dhcp
config 'dnsmasq'
	option domainneeded	 1
	option boguspriv	 1
	option filterwin2k	 0
	option localise_queries	 1
	option rebind_protection 1
	option rebind_localhost  1
	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'
...
  • 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”).

中文翻译

  • local和domain选项使得dnsmasq使用/etc/hosts文件里的条目定义来提供解析,如果DHCP配置了lan的域,那么获得地址的客户机也可以通过主机名解析。
  • domainneeded、 boguspriv、localise_qureies、以及expandhosts选项,保证了本地域名的请求,不会转发到上游域名解析服务器上。
  • authoritative选项保证了路由器成为本网络上的唯一一台DHCP服务器;客户机可以更快的获取IP地址的配置。
  • leasefile文件用于保存租约内容,这样如果dnsmasq如果重启的话就可以根据该文件重新维护租约信息。
  • resolvfile定义了dnsmasq使用的文件,该文件用于找到上游服务器,通常由WAN DHCP客户端和PPP客户端创建。
  • enable_tftp打开tftp服务,而tftp_root定义了TFTP服务器的文件根目录。你可以在客户端访问tftp服务器时,需要指定IP。在客户机,通过设定环境变量serverip来定义(e.g. setenv serverip 192.168.1.10)。
名字 类型 默认值 直接运行命令时候的选项 描述
add_local_domain boolean 1 将resolv.conf里配置的本地域名也进行解析
add_local_hostname boolean 1 将A、 AAAA、 PTR 记录 for this router only on DHCP served LAN.
:!: enhanced function available on Trunk with option add_local_fqdn
add_local_fqdn integer 1 Add A, AAAA, and PTR records for this router only on DHCP served LAN. 0 - Disable. 1 - Hostname on Primary Address. 2 - Hostname on All Addresses. 3 - FDQN on All Addresses. 4 - iface.host.domain on All Addresses.
:!: add_local_fqdn on Trunk but not 17.01.0
add_wan_fqdn integer 0 Labels WAN interfaces like add_local_fqdn instead of your ISP assigned default which may be obscure. WAN is inferred from config dhcp sections with option ignore 1 set, so they do not need to be named WAN
:!: add_wan_fqdn on Trunk but not 17.01.0
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 do not include DBus support.
dhcp_boot string (none) --dhcp-boot 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) --dhcp-hostsfile 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 --dnssec Validate DNS replies and cache DNSSEC data.
:!: Requires the dnsmasq-full package.
dnsseccheckunsigned boolean 0 --dnssec-check-unsigned 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 --enable-tftp 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 --dhcp-fqdn 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 (lowercase “L”) 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 --local-service 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 (uppercase “i”) 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 --stop-dns-rebind Enables DNS rebind attack protection by discarding upstream RFC1918 responses
rebind_localhost boolean 0 --rebind-localhost-ok 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) --rebind-domain-ok 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.
rev_server list of strings (none) --rev-server List of network range with a DNS server to forward reverse DNS 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) --tftp-root Specifies the TFTP root directory
minport integer 0 --min-port Dnsmasq picks random ports as source for outbound queries. When this option is given, the ports used will always be larger than or equal to the specified minport value (min valid value 1024). Useful for systems behind firewalls.
maxport integer 0 --max-port Dnsmasq picks random ports as source for outbound queries. When this option is given, the ports used will always be smaller than or equal to the specified maxport value (max valid value 65535). Useful for systems behind firewalls.
noping boolean 0 --no-ping By default dnsmasq checks if an IPv4 address is in use before allocating it to a host by sending ICMP echo request (aka ping) to the address in question. This parameter allows to disable this check.
allservers boolean 0 --all-servers By default, when dnsmasq has more than one upstream server available, it will send queries to just one server. Setting this parameter forces dnsmasq to send all queries to all available servers. The reply from the server which answers first will be returned to the original requeser.
quietdhcp boolean 0 --quiet-dhcp Suppress logging of the routine operation of DHCP. Errors and problems will still be logged
sequential_ip boolean 0 --dhcp-sequential-ip Dnsmasq is designed to choose IP addresses for DHCP clients using a hash of the client's MAC address. This normally allows a client's address to remain stable long-term, even if the client sometimes allows its DHCP lease to expire. In this default mode IP addresses are distributed pseudo-randomly over the entire available address range. There are sometimes circumstances (typically server deployment) where it is more convenient to have IP addresses allocated sequentially, starting from the lowest available address, and setting this parameter enables this mode. Note that in the sequential mode, clients which allow a lease to expire are much more likely to move IP address; for this reason it should not be generally used.
addmac [0,1,base64,text] 0 --add-mac Add the MAC address of the requester to DNS queries which are forwarded upstream; this may be used to do DNS filtering by the upstream server.
The MAC address can only be added if the requester is on the same subnet as the dnsmasq server. Note that the mechanism used to achieve this (an EDNS0 option) is not yet standardised, so this should be considered experimental. Also note that exposing MAC addresses in this way may have security and privacy implications.
logdhcp boolean 0 --log-dhcp Enables extra DHCP logging; logs all the options sent to the DHCP clients and the tags used to determine them

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:

config 'dhcp' 'lan'
	option 'interface'   'lan'
	option 'start'       '100'
	option 'limit'	     '150'
	option 'leasetime'   '12h'
        option ra server
        option dhcpv6 server
  • lan specifies the 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.

Name Type Required Default Description
dhcp_option list of strings no (none) The ID dhcp_option here must be with written with an underscore. It will be translated 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.
dhcp_option_force list of strings no (none) Exactly the same as dhcp_option (note the underscores), but it will be translated to --dhcp-option-force, meaning that the DHCP option will be sent regardless on whether the client requested it.
:!: dhcp_option_force on Trunk but not 17.01.0
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
dhcpv4 string no none Specifies whether DHCPv4 server should be enabled none or disabled (disabled)
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)
ra_default integer no 0 Default router lifetime in the RA message will be set if default route is present and a global IPv6 address (0) or if default route is present but no global IPv6 address (1) or neither of both conditions (2)
ra_management integer no 1 RA management mode : no M-Flag but A-Flag (0), both M and A flags (1), M flag but not A flag (2)
ra_offlink bool no 0 Announce prefixes as offlink (1) in RAs
ra_preference string no medium Announce routes with either high (high), medium (medium) or low (low) priority in RAs
ra_mininterval integer no 200 Minimum time interval between RAs (in seconds)
ra_maxinterval integer no 600 Maximum time interval between RAs (in seconds)
ra_lifetime integer no 1800 Advertised router lifetime (in seconds)
ra_useleasetime bool no 0 Limit the preferred and valid lifetimes of the prefixes in the RA messages to the configured DHCP leasetime
ra_hoplimit integer no 0 Advertised current hop limit (0-255)
ra_reachabletime integer no 0 Advertised reachable time (in milliseconds) (0-3600000)
ra_retranstime integer no 0 Advertised NS retransmission time (in milliseconds) (0-60000)
ra_mtu integer no none Maximum advertised MTU
ndp string no none Specifies whether NDP should be relayed relay or disabled none
ndproxy_routing bool no 1 Learn routes from NDP
ndproxy_slave bool no 0 Ignore neighbor messages on slave enabled (1) interfaces
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.
instance dnsmasq instance no (none) Dnsmasq instance to which the dhcp section is bound; if not specified the section is valid for all dnsmasq instances.
tag list of tag names no (none) List of tags that dnsmasq needs to match to use this dhcp-range.

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!

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.

config host
        option ip       '192.168.1.2'
        option mac      '00:11:22:33:44:55'
        option name     'mypc'

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.

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'

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
instance dnsmasq instance no (none) Dnsmasq instance to which the host section is bound; if not specified the section is valid for all dnsmasq instances.

You can specify an alternative default Gateway

config 'dhcp' 'lan'
        option 'interface' 'lan'
        option 'start' '100'
        option 'limit' '150'
        option 'leasetime' '12h'
        list 'dhcp_option' '3,192.168.1.2'

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.

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'

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.

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.
instance dnsmasq instance no (none) Dnsmasq instance to which the boot section is bound; if not specified the section is valid for all dnsmasq instances.

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.

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:

config mac 'opnvpn'
        option mac  '00:FF:*:*:*:*'
        option networkid   'opnvpn'
        list   dhcp_option '3'

And like this in UCI

dhcp.opnvpn=mac
dhcp.opnvpn.mac=00:FF:*:*:*:*
dhcp.opnvpn.networkid=opnvpn
dhcp.opnvpn.dhcp_option=3

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.

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:

dhcp-script=/sbin/action.sh

DHCP needs UDP ports 67 and 68 open from your zone to/from the firewall. See configuration_command_line_interface 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.

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'

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 DORA loop.

Solution:

  1. Create a bridge from the wireless and ethernet interfaces on your client
    • it's trivial: google it
    • you will have to add the MAC address of the bridge to /etc/config/dhcp
      • 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'
    • 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.
  2. 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:

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

config dhcp 'lan'
        ...
        option dynamicdhcp 0

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.

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.

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'

Running multiple dnsmasq instances as DNS forwarder and/or DHCPv4 server, each having their own configuration and lease list can be configured by creating multiple dnsmasq sections.
Typically in such configs each dnsmasq section will be bound to a specific interface by using the interface list; assigning sections like dhcp, host, etc to a specific dnsmasq instance is done by the instance parameter. By default dnsmasq adds the loopback interface to the interface list to listen when the --interface option is used; therefore the loopback interface needs to be excluded in one of the dnsmasq instances by using the notinterface list.

These are example settings for multiple dnsmasq instances each having their own dhcp section; dnsmasq instance main is bound to the lan interface while the dnsmasq instance guest is bound to the guest interface:

config dnsmasq 'main'
	option domainneeded '1'
	option boguspriv '1'
	option filterwin2k '0'
	option localise_queries '1'
	option rebind_protection '1'
	option rebind_localhost '1'
	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'
	option nonwildcard '1'
	list interface 'lan'

config dnsmasq 'guest'
	option domainneeded '1'
	option boguspriv '1'
	option filterwin2k '0'
	option localise_queries '1'
	option rebind_protection '1'
	option rebind_localhost '1'
	option local '/guest/'
	option domain 'guest'
	option expandhosts '1'
	option nonegcache '0'
	option authoritative '1'
	option readethers '1'
	option leasefile '/tmp/dhcp.leases.guest'
	option resolvfile '/tmp/resolv.conf.guest'
	option strictorder '1'
	option nonwildcard '1'
	list interface 'guest'
	list notinterface 'lo'

config dhcp 'lan'
	option instance 'main'
	option interface 'lan'
	option start '100'
	option limit '150'
	option leasetime '12h'

config dhcp 'guest_private'
	option instance 'guest'
	option interface 'guest'
	option start '100'
	option limit '150'
	option leasetime '12h'
...

The web interface (luci) has not been updated to support multiple dnsmasq instances.

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
config dhcp lan
  option interface lan
  option start 1441793
  option limit 253

Test:

root@lede:~# 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

Assign different dhcp-options to a single MAC address:

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

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

Assign different dhcp-options to multiple hosts:

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.

:!: Generally, specifying a dhcp option without any value, would disable that option. so for example you can use:

list dhcp_option '3'

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.

config dnsmasq
       ...
       option port 0
       option domain ''

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:

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"       

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.

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.

This website uses cookies. By using the website, you agree with storing cookies on your computer. Also you acknowledge that you have read and understand our Privacy Policy. If you do not agree leave the website.More information about cookies
  • Last modified: 2020/10/08 10:59
  • by tmomas