dnsmasq

由 datahunter 在三, 24/10/2012 - 07:05 發表

最後更新: 2023-12-01

介紹

A lightweight caching DNS server & DHCP server

Installed size: 282 k

* It will loads the contents of /etc/hosts

Installation

# R8

dnf install dnsmasq

Check Version

dnsmasq -v

Dnsmasq version 2.78 ...

Reload

No way to reload the configuration file without killing and restarting the dnsmasq process

The -HUP signal only reloads the /etc/hosts.conf and /etc/resolv.conf

Reason is that dnsmasq starts as root, does all the things that need root permissions

(like opening sockets on priviledged ports and opening the DHCP lease file) and then permanently changes it's identity from root to nobody.

Test Config File(--test)

Read and syntax check configuration file(s).

dnsmasq --test

dnsmasq: syntax check OK.

基本設定

/etc/dnsmasq.conf

# 當是用作 DNS cacher 時, 此會更安全

listen-address=127.0.0.1

# Never forward plain names (without a dot or domain part) to upstream nameservers.
# 當問的不是 domain 時只回應 /etc/hosts 的內容

domain-needed

# 當 result 係 private IP ranges 時, 只 /etc/hosts 內有的才會覆

bogus-priv

# filter useless windows-originated DNS requests
# This blocks all SRV, SOA requests

filterwin2k

# forces dnsmasq to try each query with each server strictly in the order

strict-order

# upstream servers from somewhere

resolv-file=/etc/resolv.conf.dnsmasq

# don't want dnsmasq to read /etc/resolv.conf or "--resolv-file=<file>"
# 到時只會食 command line 及 dnsmasq configuration file 內的設定
#no-resolv

# No to poll resolv.conf for changes and re-read them
# (當有 --resolv-file 時就檢查它指定的那個檔案)
# If --no-poll is set SIGHUP also re-reads /etc/resolv.conf. SIGHUP does NOT re-read the configuration file.
# "poll" allows the DNS servers to be set dynamically by PPP or DHCP since both protocols provide the information.

no-poll

# Add other name servers here, with domain specs if they are for non-public domains.

#server=/localnet/192.168.0.1

Listen 的設定

# Repeat the line for more than one interface

interface=eth1

當使用 "interface=X" 時, Dnsmasq 會自動加入 interface=lo

# 配合 interface 一起用, 那 NIC 只提供 DNS

no-dhcp-interface=eth1

# dnsmasq binds the wildcard address (0.0.0.0)
# even when it is listening on only some interfaces. (default behavior)
# It then discards requests that it shouldn't reply to.
# (advantage: working even when interfaces come and go and change address)
# This option forces dnsmasq to really bind only the interfaces it is listening on.

bind-interfaces

# Listen on the given IP address(es).
# Both --interface and --listen-address options may be given,
# in which case the set of both interfaces and addresses is used.
# Note
# if no --interface option is given, but --listen-address is,
# dnsmasq will not automatically listen on the loopback interface.
# dnsmasq automatically adds the loopback (local) interface to the list of interfaces to use
# when the --interface option is used.

listen-address=127.0.0.1
listen-address=192.168.200.254

Notes

[1]

如果只想 Listen 某 NIC, 唔建議用 "interface" & "no-dhcp-interface"
因為在 boot 機時有 NIC 未 start 會令 dnsmasq FAILED

/var/log/messages

... dnsmasq[959]: dnsmasq: unknown interface lxcbr0
... dnsmasq[959]: FAILED to start up

/etc/dnsmasq.conf

interface=lxcbr0
no-dhcp-interface=lxcbr0

[2]

* 當沒有 "--interface" 或 " --listen-address" 設定時, 除 "--except-interface" 指定的 NIC 都會 listen

[3] Local cacher settings

/etc/dnsmasq.d/my.conf

resolv-file=/etc/resolv.conf.dnsmasq
domain-needed
bogus-priv
no-poll
bind-interfaces
interface=lo

Log & Debug

# 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-async[=<lines>]

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.

SIGUSR2

When it is logging direct to a file (see --log-facility ) dnsmasq will close and reopen the log file.
(log rotate without stopping dnsmasq)

Debug

# For debugging purposes
log-queries
log-dhcp

Local domain name

Local Domain

# Add domains which you want to force to an IP address
# queries in these domains are answered from /etc/hosts or DHCP only
address=/doubleclick.net/127.0.0.1

# no-hosts  ( 只影響 /etc/hosts, 不影響 "addn-hosts" )

# Additional hosts file.
# Read the specified file as well as /etc/hosts. If -h is given,
# read only the specified file.
# This option may be repeated for more than one additional hosts file.
# If a directory is given, then read all the files contained in that directory.
addn-hosts=/etc/banner_hosts
addn-hosts=/etc/myhosts

# local-only domains
# queries in these domains are answered from /etc/hosts or DHCP only
local=/localnet/

# domain automatically added to simple names in a hosts-file
# 沒有加 expand-hosts 時, ping result 如下
# ping timpc            <= Success
# ping timpc.localnet   <= Fail
expand-hosts

Linux 主機設定自己的 Default Domain

search lan

Include

# Include a another lot of configuration options.
#conf-file=/etc/dnsmasq.myconfig.conf
#conf-dir=/etc/dnsmasq.d

--address 與 --server 分別

-S, --local, --server=[/[<domain>]/[domain/]][<ipaddr>[#<port>]

Specify IP address of upstream servers directly. Setting this flag does not suppress reading of /etc/resolv.conf

If one or more optional domains are given, that server is used only for those domains and

they are queried only using the specified server.

i.e.

--server=/google.com/1.2.3.4
--server=/www.google.com/#

# will send queries for *.google.com to 1.2.3.4, except *www.google.com
# The special server address '#' means, "use the standard servers"

Remark

An empty domain specification, "//" has the special meaning of "unqualified names only" ie names without any dots in them.

"--server=/example.com/" returns NXDOMAIN for example.com and all its subdomains.

Cache Settings

# Set the cachesize here. (The default is 150 names)
cache-size=1024

# Negative caching (no such domain)
#no-negcache

hard code cache limit (cache-size)

10000 entries

測試

dig datahunter.org | grep "Query time"

;; Query time: 168 msec

dig datahunter.org | grep "Query time"

;; Query time: 0 msec

統計

SIGUSR1 # dnsmasq writes statistics to the system log.

killall -SIGUSR1 dnsmasq

Nov 20 12:31:08 myserver dnsmasq[15267]: time 1574224268
Nov 20 12:31:08 myserver dnsmasq[15267]: cache size 10000, 0/254 cache insertions re-used unexpired cache entries.
Nov 20 12:31:08 myserver dnsmasq[15267]: queries forwarded 548, queries answered locally 394
Nov 20 12:31:08 myserver dnsmasq[15267]: queries for authoritative zones 0
Nov 20 12:31:08 myserver dnsmasq[15267]: server 8.8.8.8#53: queries sent 374, retried or failed 0
Nov 20 12:31:08 myserver dnsmasq[15267]: server 8.8.4.4#53: queries sent 214, retried or failed 0

N/M

the number of names which have had to removed from the cache before they expired
in order to make room for new names

M:
the total number of names that have been inserted into the cache.

SIGHUP # refresh the cache

dnsmasq clears its cache and then re-loads some config

(/etc/hosts, /etc/ethers, /etc/resolv.conf --dhcp-* --addn-hosts, --hostsdir)

--min-cache-ttl=<time>

Extend short TTL values to the time given when caching them.

i.e.

--min-cache-ttl=600

This will cause all DNS records to be considered valid for 10 minutes.

dnsmasq 的 DHCP 設定

By default, the DHCP server will attempt to ensure that an address is not in use before allocating it to a host.

It does this by sending an ICMP echo request (aka "ping") to the address in question.

udp port 67 (bootps) <-- (client 找 server 時 broadcast 出去)

DHCPDISCOVER (1,9,13,16s)
DHCPREQUEST

udp port 68 (bootpc) <-- (client listen server broadcast 回來的資料的 port)

DHCPOFFER
DHCPACK

Diagram:

Server: 192.168.1.1

Client: 192.168.1.101

[1] Client request

UDP 0.0.0.0:68 -> 255.255.255.255:67

[2] Server responds

UDP 192.168.1.1:67 -> 255.255.255.255:68

[3] Client reply

UDP 192.168.1.101:67 -> 192.168.1.1:68

設定:

# Set the domain for dnsmasq. Allows DHCP hosts to have fqdn
domain=localnet

dhcp-range=10.1.1.51,10.1.1.150,12h

# Set Gateway
# option:router => 3
# dhcp-option=option:router,10.1.1.254
dhcp-option=3,10.1.1.254

# Set DNS
dhcp-option=6,8.8.8.8,8.8.4.4

# maximum number of DHCP leases
# For prevent DoS. The default is 1000
dhcp-lease-max=150

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

DHCP Leases

-X, --dhcp-lease-max=<number>

Limits dnsmasq to the specified maximum number of DHCP leases. The default is 1000.

This limit is to prevent DoS attacks from hosts which create thousands of leases and use lots of memory in the dnsmasq process.

/var/lib/misc/dnsmasq.leases

/var/db/dnsmasq.leases

Disable DHCP

方式 1

Comment out "dhcp-range="

# dhcp-range=192.168.0.100,192.168.0.199,1h

方式 2

唔建議, 因為 boot 機時 lxcbr0 未存在

no-dhcp-interface=lxcbr0

Assign Static IP by MAC

dhcp-host=aa:bb:cc:dd:ee:ff,192.168.123.241

Usage

# lease: m, h, infinite

dhcp-host=11:22:33:44:55:66,fred,192.168.0.60,45m

# 更新 IP openwrt

/etc/init.d/dnsmasq stop

vim /tmp/dhcp.leases

刪除 aa:bb:cc:dd:ee:ff 那行

/etc/init.d/dnsmasq start

Per MAC Settings

用 "set:<tag>"

dhcp-host=<hwaddr>,set:<tag>,<ipaddr>[,<hostname>][,<lease_time>]

用 "tag:<tag>"

dhcp-boot=tag:<tag>,<filename>,<servername>,<server address>

i.e.

#### PXE
# u16
dhcp-option=tag:u16,17,iscsi:192.168.123.10::::iqn.2018-03.local.home:u16
dhcp-option=tag:u16,203,iqn.2018-03.local.u16
dhcp-host=88:88:88:88:88:56,set:u16,192.168.123.56,u16,infinite

# u16b
dhcp-boot=tag:u16b,pxelinux.0,pxeserver,192.168.123.10
dhcp-host=88:88:88:88:88:57,set:u16b,192.168.123.57,u16b,infinite

dhcp-match

Usage

dhcp-match=<network-id>,<option number>[,<value>]

Without a value, set the network-id tag if the client sends a DHCP option of the given number

   When a value is given, set the tag only if the option is sent and matches the value.

   The value may be of the form "01:ff:*:02" in which case the value must match (apart from widcards) but the option sent may have unmatched

i.e.

# will set the tag "efi-ia32" if the the number 6 appears in the list of architectures sent by the client in option 93.

dhcp-match=efi-ia32,93,6

# load undionly.kpxe for clients not tagged with 'iPXE'

dhcp-match=set:ipxe,77,iPXE
dhcp-boot=tag:!ipxe,undionly.kpxe
dhcp-boot=http://10.37.129.3/bootstrap.ipxe

Doc

man 8 dnsmasq

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dnsmasq

介紹

目錄

Installation

Reload

Test Config File(--test)

基本設定

Listen 的設定

Log & Debug

Local domain name

Cache Settings

dnsmasq 的 DHCP 設定

Assign Static IP by MAC

Per MAC Settings

dhcp-match

Doc