DNSmasq – 配置DNS和DHCP

DNSmasq是一个小巧且方便地用于配置DNS和DHCP的工具，适用于小型网络。它提供了DNS功能和可选择的DHCP功能可以取代dhcpd(DHCPD服务配置)和bind等服务，配置起来更简单，更适用于虚拟化和大数据环境的部署。

dhcp服务

其中一些关键的配置如下,配置文件/etc/dnsmasq.conf 中的注释已经给出了非常详细的解释。

		
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								# 服务监听的网络接口地址

								# If you want dnsmasq to listen for DHCP and DNS requests only on

								# specified interfaces (and the loopback) give the name of the

								# interface (eg eth0) here.

								# Repeat the line for more than one interface.

								#interface=

								# Or you can specify which interface _not_ to listen on

								#except-interface=

								# Or which to listen on by address (remember to include 127.0.0.1 if

								# you use this.)

								listen-address=192.168.1.132,127.0.0.1

								# dhcp动态分配的地址范围

								# Uncomment this to enable the integrated DHCP server, you need

								# to supply the range of addresses available for lease and optionally a lease time

								dhcp-range=192.168.1.50,192.168.1.150,48h

								# dhcp服务的静态绑定

								# Always set the name and ipaddr of the host with hardware address

								# dhcp-host=00:0C:29:5E:F2:6F,192.168.1.201

								# dhcp-host=00:0C:29:5E:F2:6F,192.168.1.201,infinite 无限租期

								dhcp-host=00:0C:29:5E:F2:6F,192.168.1.201,os02

								dhcp-host=00:0C:29:15:63:CF,192.168.1.202,os03

								# 设置默认租期

								# Set the limit on DHCP leases, the default is 150

								#dhcp-lease-max=150

								# 租期保存在下面文件

								# The DHCP server needs somewhere on disk to keep its lease database.

								# This defaults to a sane location, but if you want to change it, use

								# the line below.

								#dhcp-leasefile=/var/lib/dnsmasq/dnsmasq.leases

								# 通过/etc/hosts来分配对应的hostname

								# Enable the address given for "judge" in /etc/hosts

								# to be given to a machine presenting the name "judge" when

								# it asks for a DHCP lease.

								#dhcp-host=judge

								# 忽略下面MAC地址的DHCP请求

								# Never offer DHCP service to a machine whose ethernet

								# address is 11:22:33:44:55:66

								#dhcp-host=11:22:33:44:55:66,ignore

								# dhcp所在的domain

								# Set the domain for dnsmasq. this is optional, but if it is set, it

								# does the following things.

								# 1) Allows DHCP hosts to have fully qualified domain names, as long

								#     as the domain part matches this setting.

								# 2) Sets the "domain" DHCP option thereby potentially setting the

								#    domain of all systems configured by DHCP

								# 3) Provides the domain part for "expand-hosts"

								domain=debugo.com

								# 设置默认路由出口

								# dhcp-option遵循RFC 2132（Options and BOOTP Vendor Extensions),可以通过dnsmasq --help dhcp来查看具体的配置

								# 很多高级的配置，如iSCSI连接配置等同样可以由RFC 2132定义的dhcp-option中给出。

								# option 3为default route

								# Override the default route supplied by dnsmasq, which assumes the

								# router is the same machine as the one running dnsmasq.

								dhcp-option=3,192.168.0.1

								# 设置NTP Server.这是使用option name而非选项名来进行设置

								# Set the NTP time server addresses to 192.168.0.4 and 10.10.0.5

								#dhcp-option=option:ntp-server,192.168.0.4,10.10.0.5

注意:当为某一MAC地址同时静态分配主机名和IP时，如果写到两条dhcp-host选项里（如下所示），则只会生效后面的一条。正确的选项写法如上配置。

		
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								dhcp-host=00:0C:29:5E:F2:6F,192.168.1.201

								dhcp-host=00:0C:29:5E:F2:6F,os02

重新启动客户端网卡。由于之前测试中客户端网卡已经申请了DHCP租期。所以这里需要修改租期文件，让客户端重新获得IP和hostname。

		
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								[root@server] vim /var/lib/dnsmasq/dnsmasq.leases

								1400240493 00:0c:29:5e:f2:6f 192.168.1.143 os02 *

								1400240498 00:0c:29:15:63:cf 192.168.1.52 os01 *

启动dnsmasq服务（server的IP为192.168.1.132）

		
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								[root@server] dnsmasq

下面在客户端进行测试：
# 确保网络接口配置使用dhcp方式

		
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								[root@localhost] cat /etc/sysconfig/network-scripts/ifcfg-eth1

								DEVICE="eth1"

								BOOTPROTO=dhcp

								IPV6INIT=no

								NM_CONTROLLED=no

								ONBOOT="yes"

								TYPE="Ethernet"

								# 重启网络服务

								[root@localhost] service network restart

								Shutting down interface eth0:                              [  OK  ]

								Shutting down loopback interface:                          [  OK  ]

								Bringing up loopback interface:                            [  OK  ]

								Bringing up interface eth0:  

								Determining IP information for eth1... done.

								# 检查IP地址                                                           [  OK  ]

								[root@os03] ifconfig

								eth1      Link encap:Ethernet  HWaddr 00:0C:29:15:63:D9  

								          inet addr:192.168.1.202  Bcast:192.168.1.255  Mask:255.255.255.0

								          inet6 addr: fe80::20c:29ff:fe15:63d9/64 Scope:Link

								          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

								          RX packets:251 errors:0 dropped:0 overruns:0 frame:0

								          TX packets:43 errors:0 dropped:0 overruns:0 carrier:0

								          collisions:0 txqueuelen:1000 

								          RX bytes:36077 (35.2 KiB)  TX bytes:4598 (4.4 KiB)

								......

								# 检查默认路由

								[root@os03] route -n

								Kernel IP routing table

								Destination     Gateway         Genmask         Flags Metric Ref    Use Iface

								192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1

								169.254.0.0     0.0.0.0         255.255.0.0     U     1002   0        0 eth1

配置DNS服务

dnsmasq能够缓存外部DNS记录，同时提供本地DNS解析或者作为外部DNS的代理，即dnsmasq会首先查找/etc/hosts等本地解析文件，然后再查找/etc/resolv.conf等外部nameserver配置文件中定义的外部DNS。所以说dnsmasq是一个很不错的DNS中继。DNS配置同样写入dnsmasq.conf配置文件里。

		
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								# 本地解析文件

								# If you don't want dnsmasq to read /etc/hosts, uncomment the following line.

								#no-hosts

								# or if you want it to read another file, as well as /etc/hosts, use this.

								#addn-hosts=/etc/banner_add_hosts

								# Set this (and domain: see below) if you want to have a domain

								# automatically added to simple names in a hosts-file.

								# 例如，/etc/hosts中的os01将扩展成os01.debugo.com

								expand-hosts

								# Add local-only domains here, queries in these domains are answered

								# from /etc/hosts or DHCP only.

								local=/debugo.com/

								# 强制使用完整的解析名

								# Never forward plain names (without a dot or domain part)

								domain-needed

								# 添加额外的上级DNS主机（nameserver）配置文件

								# Change this line if you want dns to get its upstream servers from

								# somewhere other that /etc/resolv.conf

								#resolv-file=

								# 不使用上级DNS主机配置文件(/etc/resolv.conf和resolv-file）

								# If you don't want dnsmasq to read /etc/resolv.conf or any other

								# file, getting its servers from this file instead (see below), then

								# uncomment this.

								no-resolv

								# 相应的，可以为特定的域名指定解析它的nameserver。一般是其他的内部DNS name server

								# Add other name servers here, with domain specs if they are for

								# non-public domains.

								# server=/myserver.com/192.168.0.1

								# 设置DNS缓存大小（单位：DNS解析条数）

								#Set the size of dnsmasq's cache. The default is 150 names. Setting the cache size to zero disables caching.

								cache-size=500

								# 关于log的几个选项

								# For debugging purposes, log each DNS query as it passes through

								# dnsmasq.

								log-queries

								# Log lots of extra information about DHCP transactions.

								#log-dhcp

								# Log to this syslog facility or file. (defaults to DAEMON)

								log-facility=/var/log/dnsmasq.log

								# 异步log，缓解阻塞，提高性能。

								# Enable asynchronous logging and optionally set the limit on the number of lines which will be queued by dnsmasq

								# when writing to the syslog is slow. 

								# Dnsmasq can log asynchronously: this allows it to continue functioning without being blocked by syslog, 

								# and allows syslog to use dnsmasq for DNS queries without risking deadlock. If the queue of log-lines becomes 

								# full, dnsmasq will log the overflow, and the number of messages lost. 

								# The default queue length is 5, a sane value would be 5-25, and a maximum limit of 100 is imposed.

								log-async=20

								# 指定domain的IP地址

								# Add domains which you want to force to an IP address here.

								# The example below send any host in doubleclick.net to a local

								# webserver.

								address=/doubleclick.net/127.0.0.1

								address=/.phobos.apple.com/202.175.5.114

配置完成后重启dnsmasq，然后在客户端测试：

		 
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								[root@os03] nslookup os01.debugo.com

								Server: 192.168.1.132

								Address: 192.168.1.132#53

								Name: os01.debugo.com

								Address: 192.168.1.132

								[root@os03] nslookup os02.debugo.com

								Server: 192.168.1.132

								Address: 192.168.1.132#53

								Name: os02.debugo.com

								Address: 192.168.1.201

								[root@os03] nslookup doubleclick.net

								Server: 192.168.1.132

								Address: 192.168.1.132#53

								Name: doubleclick.net

								Address: 127.0.0.1

								#注意，由于address选项解析为127.0.0.1，而非server的192.168.1.132地址。

								[root@os03] nslookup a1.phobos.apple.com

								Server: 192.168.1.132

								Address: 192.168.1.132#53

								Name: a1.phobos.apple.com

								Address: 202.175.5.114

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