dhcpd

関連記事

• dhcpcd

dhcpd は Internet Systems Consortium による DHCP サーバーです。LAN 上でルーターとして動作するマシンなどで有用です。

インストール

公式リポジトリの dhcp パッケージをインストールしてください。

設定

使用したいインターフェイスに固定 IPv4 アドレスを割り当ててください (このページでは例として eth0 を使います)。アドレスの最初の3バイトを他のインターフェイスのアドレスと全く同じにすることはできません。

# ip link set up dev eth0
# ip addr add 139.96.30.100/24 dev eth0 # arbitrary address

ヒント: Usually, the one of next three subnets is used for private networks, which are specially reserved and won't conflict with any host in the Internet:

• 192.168/16 (subnet 192.168.0.0, netmask 255.255.0.0)
• 172.16/12 (subnet 172.16.0.0, netmask 255.240.0.0)
• 10/8 (for large networks; subnet 10.0.0.0, netmask 255.0.0.0)

See also RFC 1918.

起動時に固定 ip を割り当てるには、ネットワーク設定#固定 IP アドレスを参照。

デフォルトの dhcpd.conf にはアンコメントされている例がたくさん含まれているので、ファイルを移動してください:

# mv /etc/dhcpd.conf /etc/dhcpd.conf.example

最小限の設定ファイルは以下のようになります:

/etc/dhcpd.conf

option domain-name-servers 8.8.8.8, 8.8.4.4;
option subnet-mask 255.255.255.0;
option routers 139.96.30.100;
subnet 139.96.30.0 netmask 255.255.255.0 {
  range 139.96.30.150 139.96.30.250;
}

domain-name-servers option contains addresses of DNS servers which are supplied to clients. In our example we are using Google's public DNS servers. If you know a local DNS servers (for example, provided by your ISP), you should use it. If you've configured your own DNS on a local machine, then use its address in your subnet (e. g. 139.96.30.100 in our example).

subnet-mask and routers defines a subnet mask and a list of available routers on the subnet. In most cases for small networks you can use 255.255.255.0 as a mask and specify an IP address of the machine on which you're configuring DHCP server as a router.

subnet blocks defines options for separate subnets, which are mapped to the network interfaces on which dhcpd is running. In our example this is one subnet 139.96.30.0/24 for single interface eth0, for which we defined the range of available IP addresses. Addresses from this range will be assigned to the connecting clients.

設定後、systemctl を使って dhcpd4.service を起動することで dhcpd デーモンを起動できます。任意で、ブート時に自動的に起動するように有効化してください。

Now, to any computer you connect to the eth0 will be assigned an IPv4 address (from 139.96.30.150 to 139.96.30.250 in this example).

Tips and Tricks

Listening on only one interface

If your computer is already part of one or several networks, it could be a problem if your computer starts giving ip addresses to machines from the other networks. It can be done by either configuring dhcpd or starting it as a daemon with systemctl.

dhcpd の設定

In order to exclude an interface, you must create an empty declartion for the subnet that will be configured on that interface.

This is done by editing the configuration file (for example):

/etc/dhcpd.conf

# No DHCP service in DMZ network (192.168.2.0/24)
subnet 192.168.2.0 netmask 255.255.255.0 {
}

サービスファイル

There is no service files provided by default to use dhcpd only on one interface so you need to create one:

 /etc/systemd/system/dhcpd4@.service

[Unit]
Description=IPv4 DHCP server on %I
Wants=network.target
After=network.target

[Service]
Type=forking
PIDFile=/run/dhcpd4.pid
ExecStart=/usr/bin/dhcpd -4 -q -pf /run/dhcpd4.pid %I
KillSignal=SIGINT

[Install]
WantedBy=multi-user.target

Now you can start dhcpd as a daemon which only listen to a specific interface, for example eth0.

# systemctl start dhcpd4@eth0.service