setup.html - vendor/opensource/dnsmasq - Git at Google

 <HTML>
 <HEAD>
 <TITLE> Configuring Dnsmasq.</TITLE>
 </HEAD>
 <BODY BGCOLOR="WHITE">
 <H1 ALIGN=center>Dnsmasq setup</H1>
 <H2>Installation.</H2>
 To compile and install dnsmasq, the following command (as root) is enough.

 <PRE>
 make install
 </PRE>

 You might want to edit config.h. Dnsmasq has
 been run on (at least) Linux, uCLinux, AIX 4.1.5, FreeBSD 4.4 OpenBSD and Tru64 4.x

 Dnsmasq is normally  run on a firewall machine (the machine with the
 modem or other connection to your ISP.) but it can run on any machine
 with access to the ISPs nameservers.

 Put the binary in <TT>/usr/local/sbin/dnsmasq</TT> (running <TT>make install</TT>  will do this) and arrange for it
 to be started at boot time.

 Note that dnsmasq needs to run as root, since it binds privileged ports. It will drop root privileges after start-up. Dnsmasq
 logs problems using the syslog facility as a daemon. It logs debugging
 information to local0
 <P>
 <H2>Configuration.</H2>
 Configuration for dnsmasq is pretty simple in almost all cases. The
 program has collected a fair few options as it has developed but most of them
 are not needed most of the time. A machine which already has a DNS
 configuration (ie one or more external nameservers in <TT>/etc/resolv.conf</TT>
 and any local hosts in <TT>/etc/hosts</TT>) can be turned into a nameserver
 simply by running dnsmasq, with no options or configuration at
 all. Set the IP address of the machine running dnsmasq as the DNS
 server in all the other machines on your network, and you're done.
 <P>
 With a few option flags, it is possible to make dnsmasq do more clever
 tricks. Options for dnsmasq can be set either on the command line
 when starting dnsmasq, or in its configuration file, <TT>/etc/dnsmasq.conf</TT>.

 <h2>Making the nameserver machine use dnsmasq.</h2>
 In the simple configuration described above, processes local to the
 machine will not use dnsmasq, since they get their information about
 which nameservers to use from /etc/resolv.conf, which is set to the
 upstream nameservers. To fix this, simply replace the nameserver in
 <TT>/etc/resolv.conf</TT> with the local address 127.0.0.1 and give the
 address(es) of the upstream nameserver(s) to dnsmasq directly. You can
 do this using either the <TT>server</TT> option, or by putting them into
 another file, and telling  dnsmasq about its location with
 the <TT>resolv-file</TT> option.

 <h2>Automatic nameserver configuration.</h2>
 The two protocols most used for automatic IP network configuration
 (PPP and DHCP) can determine the IP addresses for nameservers automatically.
 The daemons can be made to write out a file in the resolv.conf format with the
 nameservers in which is perfect for dnsmasq to use. When the
 nameservers change, for instance on dialling into a new ISP using PPP,
 dnsmasq will automatically re-read this file and begin using the new
 nameserver(s) completely transparently.

 <h3>Automatic DNS server configuration with PPP.</h3>
 Later versions of pppd have an option "usepeerdns" which instructs it to write a file containing
 the address(es) of the DNS severs in <TT>/etc/ppp/resolv.conf</TT>. Configure dnsmasq
 as above with "nameserver 127.0.0.1" in <TT>/etc/resolv.conf</TT> and run dnsmasq
 with to option <TT>resolv-file=/etc/ppp/resolv.conf</TT>.
 <P>
 On Redhat (at least versions 7.1, 7.2 and 7.3) you can set pppd
 options by adding "PPPOPTIONS=usepeerdns" to
 <TT>/etc/sysconfig/network-scripts/ifcfg-ippp0</TT>.  In the same file, make sure
 that "PEERDNS=no" to stop RedHat's network initscripts from copying
 <TT>/etc/ppp/resolv.conf</TT> into <TT>/etc/resolv.conf</TT>.<BR>

 On SuSE (at least version 8.1, and 8.2) you should use YaST to activate
 <TT>[x] Modify DNS when connected</TT> then stop SuSEs network initscripts
 from copying <TT>/etc/ppp/resolv.conf</TT> into <TT>/etc/resolv.conf</TT>
 by modifying MODIFY_RESOLV_CONF_DYNAMICALLY="no" in <TT>/etc/sysconfig/network/config</TT>.


 <h3>Automatic DNS server configuration with DHCP.</h3>
 You need to get your DHCP client to write the addresse(s) of the DNS
 servers to a file other than <TT>/etc/resolv.conf</TT>. For dhcpcd, the
 <TT>dhcpcd.exe</TT> script gets run with the addresses of the nameserver(s) in
 the shell variable <TT>$DNS</TT>. The following bit of shell script
 uses that to write a file suitable for dnsmasq.
 <PRE>

 echo -n >|/etc/dhcpc/resolv.conf
 dnsservs=${DNS//,/ }
 for serv in $dnsservs; do
     echo "nameserver $serv" >>/etc/dhcpc/resolv.conf
 done

 </PRE>

 Remember to give dhcpcd the <TT>-R</TT> flag to stop it overwriting
 <TT>/etc/resolv.conf</TT>.

 <P>
 For other DHCP clients it should be possible to achieve the same effect.

 <h3> DHCP and PPP.</h3>
 On a laptop which may potentially connect via a modem and PPP or
 ethernet and DHCP it is possible to combine both of the above
 configurations. Running dnsmasq with the flags
 <TT>resolv-file=/etc/ppp/resolv.conf resolv-file=/etc/dhcpc/resolv.conf</TT>
 makes it poll <B>both</B> files and use whichever was updated
 last. The result is automatic switching between DNS servers.
 </H3>

 <H2> Integration with DHCP.</H2>
 Dnsmasq reads <TT>/etc/hosts</TT> so that the names of local machines are
 available in DNS. This is fine when you give all your local machines
 static IP addresses which can go in <TT>/etc/hosts</TT>, but it doesn't work
 when local machines are configured via DHCP, since the IP address
 allocated to machine is not fixed. Dnsmasq comes with an integrated
 DHCP daemon to solve this problem.
 <P>
 The dnsmasq DHCP daemon allocates addresses to hosts on the network and tries
 to determine their names. If it succeeds it add the name and address
 pair to the DNS. There are basically two ways to associate a name with
 a DHCP-configured machine; either the machine knows its name which it
 gets a DHCP lease, or dnsmasq gives it a name, based on the MAC
 address of its ethernet card. For the former to work, a machine needs to know its name when it
 requests a DHCP lease. For dhcpcd, the -h option specifies this. The
 names may be anything as far as DHCP is concerned, but dnsmasq adds
 some limitations. By default the names must no have a domain part, ie
 they must just be a alphanumeric name, without any dots.  This is a
 security feature to stop a machine on your network telling DHCP that
 its name is "www.microsoft.com" and thereby grabbing traffic which
 shouldn't go to it. A domain part is only allowed by dnsmasq in DHCP machine names
 if the <TT>domain-suffix</TT> option is set, the domain part must match the
 suffix.
 <P>
 As an aside, make sure not to tell DHCP to set the hostname when it
 obtains a lease (in dhcpcd that's the -H flag.)
 This is not reliable since the DHCP server gets the
 hostname from DNS which in this case is dnsmasq. There is a race
 condition because the host's name in the DNS may change as a
 result of it getting a DHCP lease, but this does not propagate before
 the name is looked up. The net effect may be that the host believes it
 is called something different to its name in the DNS. To be safe, set
 the hostname on a machine locally, and pass the same name to DHCP when
 requesting a lease.
 <P>
 <H2>Setting up a mailhub.</H2>
 If you generate mail on the machines attached to your private network, you may
  be interested in the MX record feature of dnsmasq. This allows you to have all
  the machines on your network use your firewall or another machine as a "smarthost" and
 deliver mail to it. The details of how to set this up are highly dependent on
 your mailer, system and distribution. The only thing that's relevant to dnsmasq is that the mailer
 needs to be able to interrogate the DNS and find an MX record for your mailhub.
 <P>
 By giving dnsmasq the <TT>mx-host</TT> option
 you instruct dnsmasq to serve an MX record for the specified address.
 By default the MX record
 points to the machine on which dnsmasq is running, so mail delivered to that
 name will get sent to the mailer on your firewall machine. You can
 have the MX record point to another machine by using the <TT>mx-target</TT>
 option.
 <P>
 In some cases it's useful for all local machines to see an MX record
 pointing at themselves: this allows mailers which insist on an MX record and
 don't fall back to A records to deliver mail within the
 machine. These MX records are enabled using the <TT>selfmx</TT> option.

 <H2>Using special servers.</H2>
 Dnsmasq has the ability to direct DNS queries for certain domains to
 specific upstream nameservers. This feature was added for use with
 VPNs but it is fully general. The scenario is this: you have a
 standard internet connection via an ISP, and dnsmasq is configured to
 forward queries to the ISP's nameservers, then you make a VPN
 connection into your companies network, giving access to hosts inside
 the company firewall. You have access, but since many of the internal hosts
 aren't visible on the public internet, your company doesn't publish
 them to the public DNS and you can't get their IP address from the ISP
 nameservers. The solution is to use the companies nameserver for
 private domains within the company, and dnsmasq allows this. Assuming
 that internal company machines are all in the domain internal.myco.com
 and the companies nameserver is at 192.168.10.1 then the option
 <TT>server=/internal.myco.com/192.168.10.1</TT> will direct all
 queries in the internal domain to the correct nameserver. You can
 specify more than one domain in each server option. If there is
 more than one nameserver just include as many
 <TT>server</TT> options as is needed to specify them all.

 <H2>Local domains.</H2>
 Sometimes people have local domains which they do not want forwarded
 to upstream servers. This is accomodated by using server options
 without the server IP address. To make things clearer <TT>local</TT>
 is a synonym for <TT>server</TT>. For example the option
 <TT>local=/localnet/</TT> ensures that any domain name query which ends in
 <TT>.localnet</TT> will be answered if possible from
 <TT>/etc/hosts</TT> or DHCP, but never sent to an upstream server.

 <H2>Defeating wildcards in top level domains.</H2>
 In September 2003 Verisign installed a wildcard record in the .com and
 .net top level domains. The effect of this is that queries for
 unregistered .com and .net names now return the address of Verisign's
 sitefinder service, rather than a "no such domain" response. To
 restore the correct behaviour, you can tell dnsmasq the address of the
 sitefinder host and have it substitute an NXDOMAIN reply when it sees
 that address. The sitefinder address is currently  64.94.110.11, so
 giving the option <TT>bogus-nxdomain=64.94.110.11</TT> will enable
 this facility for Verisign. If other TLDs do that same thing you can
 add the correct addresses for them too. See the dnsmasq FAQ for more
 details on the <TT>bogus-nxdomain</TT> option.

 <H2>Other configuration details.</H2>
 By default dnsmasq offers DNS service on all the configured interfaces
 of a host. It's likely that you don't (for instance) want to offer a
 DNS service to the world via an interface connected to ADSL or
 cable-modem so dnsmasq allows you to specify which interfaces it will
 listen on. Use either the <TT>interface</TT> or <TT>address</TT> options to do this.
 <P>
 The <TT>filterwin2k</TT> option makes dnsmasq ignore certain DNS requests which
 are made by Windows boxen every few minutes. The requests generally
 don't get sensible answers in the global DNS and cause trouble by
 triggering dial-on-demand internet links.
 <P>
 Sending SIGHUP to the dnsmasq process will cause it to empty its cache and
 then re-load <TT>/etc/hosts</TT> and <TT>/etc/resolv.conf</TT>.
 <P> Sending SIGUSR1 (killall -10 dnsmasq) to the dnsmasq process will
 cause to write cache usage statisticss to the log, typically
 <TT>/var/log/syslog</TT> or <TT>/var/log/messages</TT>.
 <P> The <TT>log-queries</TT> option tells dnsmasq to verbosely log the queries
 it is handling and causes SIGUSR1 to trigger a complete dump of the
 contents of the cache to the syslog.

 <P>For a complete listing of options please take a look at the manpage
 dnsmasq(8).
	<HTML>
	<HEAD>
	<TITLE> Configuring Dnsmasq.</TITLE>
	</HEAD>
	<BODY BGCOLOR="WHITE">
	<H1 ALIGN=center>Dnsmasq setup</H1>
	<H2>Installation.</H2>
	To compile and install dnsmasq, the following command (as root) is enough.

	<PRE>
	make install
	</PRE>

	You might want to edit config.h. Dnsmasq has
	been run on (at least) Linux, uCLinux, AIX 4.1.5, FreeBSD 4.4 OpenBSD and Tru64 4.x

	Dnsmasq is normally run on a firewall machine (the machine with the
	modem or other connection to your ISP.) but it can run on any machine
	with access to the ISPs nameservers.

	Put the binary in <TT>/usr/local/sbin/dnsmasq</TT> (running <TT>make install</TT> will do this) and arrange for it
	to be started at boot time.

	Note that dnsmasq needs to run as root, since it binds privileged ports. It will drop root privileges after start-up. Dnsmasq
	logs problems using the syslog facility as a daemon. It logs debugging
	information to local0
	<P>
	<H2>Configuration.</H2>
	Configuration for dnsmasq is pretty simple in almost all cases. The
	program has collected a fair few options as it has developed but most of them
	are not needed most of the time. A machine which already has a DNS
	configuration (ie one or more external nameservers in <TT>/etc/resolv.conf</TT>
	and any local hosts in <TT>/etc/hosts</TT>) can be turned into a nameserver
	simply by running dnsmasq, with no options or configuration at
	all. Set the IP address of the machine running dnsmasq as the DNS
	server in all the other machines on your network, and you're done.
	<P>
	With a few option flags, it is possible to make dnsmasq do more clever
	tricks. Options for dnsmasq can be set either on the command line
	when starting dnsmasq, or in its configuration file, <TT>/etc/dnsmasq.conf</TT>.

	<h2>Making the nameserver machine use dnsmasq.</h2>
	In the simple configuration described above, processes local to the
	machine will not use dnsmasq, since they get their information about
	which nameservers to use from /etc/resolv.conf, which is set to the
	upstream nameservers. To fix this, simply replace the nameserver in
	<TT>/etc/resolv.conf</TT> with the local address 127.0.0.1 and give the
	address(es) of the upstream nameserver(s) to dnsmasq directly. You can
	do this using either the <TT>server</TT> option, or by putting them into
	another file, and telling dnsmasq about its location with
	the <TT>resolv-file</TT> option.

	<h2>Automatic nameserver configuration.</h2>
	The two protocols most used for automatic IP network configuration
	(PPP and DHCP) can determine the IP addresses for nameservers automatically.
	The daemons can be made to write out a file in the resolv.conf format with the
	nameservers in which is perfect for dnsmasq to use. When the
	nameservers change, for instance on dialling into a new ISP using PPP,
	dnsmasq will automatically re-read this file and begin using the new
	nameserver(s) completely transparently.

	<h3>Automatic DNS server configuration with PPP.</h3>
	Later versions of pppd have an option "usepeerdns" which instructs it to write a file containing
	the address(es) of the DNS severs in <TT>/etc/ppp/resolv.conf</TT>. Configure dnsmasq
	as above with "nameserver 127.0.0.1" in <TT>/etc/resolv.conf</TT> and run dnsmasq
	with to option <TT>resolv-file=/etc/ppp/resolv.conf</TT>.
	<P>
	On Redhat (at least versions 7.1, 7.2 and 7.3) you can set pppd
	options by adding "PPPOPTIONS=usepeerdns" to
	<TT>/etc/sysconfig/network-scripts/ifcfg-ippp0</TT>. In the same file, make sure
	that "PEERDNS=no" to stop RedHat's network initscripts from copying
	<TT>/etc/ppp/resolv.conf</TT> into <TT>/etc/resolv.conf</TT>.<BR>

	On SuSE (at least version 8.1, and 8.2) you should use YaST to activate
	<TT>[x] Modify DNS when connected</TT> then stop SuSEs network initscripts
	from copying <TT>/etc/ppp/resolv.conf</TT> into <TT>/etc/resolv.conf</TT>
	by modifying MODIFY_RESOLV_CONF_DYNAMICALLY="no" in <TT>/etc/sysconfig/network/config</TT>.


	<h3>Automatic DNS server configuration with DHCP.</h3>
	You need to get your DHCP client to write the addresse(s) of the DNS
	servers to a file other than <TT>/etc/resolv.conf</TT>. For dhcpcd, the
	<TT>dhcpcd.exe</TT> script gets run with the addresses of the nameserver(s) in
	the shell variable <TT>$DNS</TT>. The following bit of shell script
	uses that to write a file suitable for dnsmasq.
	<PRE>

	echo -n >\|/etc/dhcpc/resolv.conf
	dnsservs=${DNS//,/ }
	for serv in $dnsservs; do
	echo "nameserver $serv" >>/etc/dhcpc/resolv.conf
	done

	</PRE>

	Remember to give dhcpcd the <TT>-R</TT> flag to stop it overwriting
	<TT>/etc/resolv.conf</TT>.

	<P>
	For other DHCP clients it should be possible to achieve the same effect.

	<h3> DHCP and PPP.</h3>
	On a laptop which may potentially connect via a modem and PPP or
	ethernet and DHCP it is possible to combine both of the above
	configurations. Running dnsmasq with the flags
	<TT>resolv-file=/etc/ppp/resolv.conf resolv-file=/etc/dhcpc/resolv.conf</TT>
	makes it poll <B>both</B> files and use whichever was updated
	last. The result is automatic switching between DNS servers.
	</H3>

	<H2> Integration with DHCP.</H2>
	Dnsmasq reads <TT>/etc/hosts</TT> so that the names of local machines are
	available in DNS. This is fine when you give all your local machines
	static IP addresses which can go in <TT>/etc/hosts</TT>, but it doesn't work
	when local machines are configured via DHCP, since the IP address
	allocated to machine is not fixed. Dnsmasq comes with an integrated
	DHCP daemon to solve this problem.
	<P>
	The dnsmasq DHCP daemon allocates addresses to hosts on the network and tries
	to determine their names. If it succeeds it add the name and address
	pair to the DNS. There are basically two ways to associate a name with
	a DHCP-configured machine; either the machine knows its name which it
	gets a DHCP lease, or dnsmasq gives it a name, based on the MAC
	address of its ethernet card. For the former to work, a machine needs to know its name when it
	requests a DHCP lease. For dhcpcd, the -h option specifies this. The
	names may be anything as far as DHCP is concerned, but dnsmasq adds
	some limitations. By default the names must no have a domain part, ie
	they must just be a alphanumeric name, without any dots. This is a
	security feature to stop a machine on your network telling DHCP that
	its name is "www.microsoft.com" and thereby grabbing traffic which
	shouldn't go to it. A domain part is only allowed by dnsmasq in DHCP machine names
	if the <TT>domain-suffix</TT> option is set, the domain part must match the
	suffix.
	<P>
	As an aside, make sure not to tell DHCP to set the hostname when it
	obtains a lease (in dhcpcd that's the -H flag.)
	This is not reliable since the DHCP server gets the
	hostname from DNS which in this case is dnsmasq. There is a race
	condition because the host's name in the DNS may change as a
	result of it getting a DHCP lease, but this does not propagate before
	the name is looked up. The net effect may be that the host believes it
	is called something different to its name in the DNS. To be safe, set
	the hostname on a machine locally, and pass the same name to DHCP when
	requesting a lease.
	<P>
	<H2>Setting up a mailhub.</H2>
	If you generate mail on the machines attached to your private network, you may
	be interested in the MX record feature of dnsmasq. This allows you to have all
	the machines on your network use your firewall or another machine as a "smarthost" and
	deliver mail to it. The details of how to set this up are highly dependent on
	your mailer, system and distribution. The only thing that's relevant to dnsmasq is that the mailer
	needs to be able to interrogate the DNS and find an MX record for your mailhub.
	<P>
	By giving dnsmasq the <TT>mx-host</TT> option
	you instruct dnsmasq to serve an MX record for the specified address.
	By default the MX record
	points to the machine on which dnsmasq is running, so mail delivered to that
	name will get sent to the mailer on your firewall machine. You can
	have the MX record point to another machine by using the <TT>mx-target</TT>
	option.
	<P>
	In some cases it's useful for all local machines to see an MX record
	pointing at themselves: this allows mailers which insist on an MX record and
	don't fall back to A records to deliver mail within the
	machine. These MX records are enabled using the <TT>selfmx</TT> option.

	<H2>Using special servers.</H2>
	Dnsmasq has the ability to direct DNS queries for certain domains to
	specific upstream nameservers. This feature was added for use with
	VPNs but it is fully general. The scenario is this: you have a
	standard internet connection via an ISP, and dnsmasq is configured to
	forward queries to the ISP's nameservers, then you make a VPN
	connection into your companies network, giving access to hosts inside
	the company firewall. You have access, but since many of the internal hosts
	aren't visible on the public internet, your company doesn't publish
	them to the public DNS and you can't get their IP address from the ISP
	nameservers. The solution is to use the companies nameserver for
	private domains within the company, and dnsmasq allows this. Assuming
	that internal company machines are all in the domain internal.myco.com
	and the companies nameserver is at 192.168.10.1 then the option
	<TT>server=/internal.myco.com/192.168.10.1</TT> will direct all
	queries in the internal domain to the correct nameserver. You can
	specify more than one domain in each server option. If there is
	more than one nameserver just include as many
	<TT>server</TT> options as is needed to specify them all.

	<H2>Local domains.</H2>
	Sometimes people have local domains which they do not want forwarded
	to upstream servers. This is accomodated by using server options
	without the server IP address. To make things clearer <TT>local</TT>
	is a synonym for <TT>server</TT>. For example the option
	<TT>local=/localnet/</TT> ensures that any domain name query which ends in
	<TT>.localnet</TT> will be answered if possible from
	<TT>/etc/hosts</TT> or DHCP, but never sent to an upstream server.

	<H2>Defeating wildcards in top level domains.</H2>
	In September 2003 Verisign installed a wildcard record in the .com and
	.net top level domains. The effect of this is that queries for
	unregistered .com and .net names now return the address of Verisign's
	sitefinder service, rather than a "no such domain" response. To
	restore the correct behaviour, you can tell dnsmasq the address of the
	sitefinder host and have it substitute an NXDOMAIN reply when it sees
	that address. The sitefinder address is currently 64.94.110.11, so
	giving the option <TT>bogus-nxdomain=64.94.110.11</TT> will enable
	this facility for Verisign. If other TLDs do that same thing you can
	add the correct addresses for them too. See the dnsmasq FAQ for more
	details on the <TT>bogus-nxdomain</TT> option.

	<H2>Other configuration details.</H2>
	By default dnsmasq offers DNS service on all the configured interfaces
	of a host. It's likely that you don't (for instance) want to offer a
	DNS service to the world via an interface connected to ADSL or
	cable-modem so dnsmasq allows you to specify which interfaces it will
	listen on. Use either the <TT>interface</TT> or <TT>address</TT> options to do this.
	<P>
	The <TT>filterwin2k</TT> option makes dnsmasq ignore certain DNS requests which
	are made by Windows boxen every few minutes. The requests generally
	don't get sensible answers in the global DNS and cause trouble by
	triggering dial-on-demand internet links.
	<P>
	Sending SIGHUP to the dnsmasq process will cause it to empty its cache and
	then re-load <TT>/etc/hosts</TT> and <TT>/etc/resolv.conf</TT>.
	<P> Sending SIGUSR1 (killall -10 dnsmasq) to the dnsmasq process will
	cause to write cache usage statisticss to the log, typically
	<TT>/var/log/syslog</TT> or <TT>/var/log/messages</TT>.
	<P> The <TT>log-queries</TT> option tells dnsmasq to verbosely log the queries
	it is handling and causes SIGUSR1 to trigger a complete dump of the
	contents of the cache to the syslog.

	<P>For a complete listing of options please take a look at the manpage
	dnsmasq(8).