{"id":4152,"date":"2015-10-20T08:39:53","date_gmt":"2015-10-20T13:39:53","guid":{"rendered":"http:\/\/www.poweradmin.com\/blog\/?p=4152"},"modified":"2015-09-29T08:53:58","modified_gmt":"2015-09-29T13:53:58","slug":"how-to-install-and-configure-a-dhcp-server-on-a-linux-machine-part-1","status":"publish","type":"post","link":"https:\/\/www.poweradmin.com\/blog\/how-to-install-and-configure-a-dhcp-server-on-a-linux-machine-part-1\/","title":{"rendered":"How to install and configure a DHCP Server on a Linux machine -Part 1-"},"content":{"rendered":"

Hello dear readers,<\/span><\/p>\n

In today\u2019s article I will show you how to create your Linux DHCP server. DHCP or Dynamic Host Control Protocol <\/i>is a service that provides automatic IP addressing to your network devices. The difference between assigning static IPs and using a DHCP server is that the IP assignment is done without the interference of System Administrators. By using such service you also have a centralized administration point to your whole infrastructure offering an easy way to add\/change or remove an IP address<\/i> from your hosts. Every network parameters can be automatically configured by the DHCP server: IP address, network mask, gateway, DNS servers, WINS server address, etc<\/i>. This service works using the client-server <\/i>model: the server sends messages using 67 (source) and 68 (destination) UDP port numbers while the client uses port 68 as source and port 67 as destination.<\/span><\/p>\n

One of the main principles behind this technology is the use of \u201cleased\u201d addresses<\/i>. This means that each client will be able to use a certain IP address only in the allotted time frame. Once an IP address has been assigned to a DHCP client, a lease-time duration is set<\/i>. The client will contact the DHCP server periodically to \u201crenew\u201d<\/i> its IP address. If for whatever reason, the DHCP server does not respond in time, the client will try to contact other DHCP servers by broadcasting a message throughout the network.<\/span><\/p>\n

Before an IP is assigned to a workstation, several messages are exchanged between the DHCP client and the server. The following picture displays a typical DHCP process:<\/span><\/p>\n

\"dhcp<\/a><\/p>\n

1. The client sends a DISCOVER<\/b> message in which he tries to contact any DHCP server available on the network. This is a broadcast message that uses the UDP port 67 as destination. Unless there is DHCP-Relay<\/i> configured on the network, this message will be blocked from any edge device (a router). This message can contain a desired IP address, the last used IP address and\/or the lease time duration.<\/span><\/p>\n

2. The server will respond with an OFFER<\/b> message that contains all the network parameters. This is also a broadcast message that uses the UDP port 68 as destination.<\/span><\/p>\n

3. When the client chooses a certain IP configuration, it will send a REQUEST<\/b> message to the DHCP server to inform that the specified IP address has been chosen. This message is received by all DHCP servers and thus, all will know that the client has received its reservation.<\/span><\/p>\n

4. The server will then respond with an ACK (Acknowledge)<\/b> message and the network parameters will be sent to the client.<\/span><\/p>\n

Below you will find other types of DHCP messages that can be exchanged between the client and the server:<\/span><\/p>\n

Decline<\/i><\/b> \u2013 the client will refuse to accept the IP allocation because this network address is used by another workstation<\/span><\/p>\n

NACK<\/i> <\/b>\u2013 this type of message is sent when the server refuses to lease an IP address<\/span><\/p>\n

Inform<\/i><\/b>\u2013 when certain network parameters must be changed, the client will send an inform message to the server<\/span><\/p>\n

Release<\/i> <\/b>\u2013 the client will inform the server that he doesn\u2019t need the reservation anymore<\/span><\/p>\n

BASIC NETWORK SETUP<\/i><\/b><\/span><\/h2>\n

For this example, I will install the DHCP server on a CentOS machine<\/i>, you can choose whatever distribution you like because the configuration procedure is similar. You\u2019ll need an active Internet connection if you choose to install the DHCP service using the yum<\/i> utility. You can also choose to install the packet from sources, but I will not cover this part right now<\/span><\/p>\n

To configure the network parameters, use eitherifconfig<\/i><\/b> or ip<\/i><\/b> command, as follows:<\/span><\/p>\n

ifconfig eth0 10.10.10.50 network 255.255.255.0<\/i><\/b><\/span><\/p>\n

ip address add 10.10.10.50\/24 dev eth0<\/i><\/b><\/span><\/p>\n

\"ifconfig<\/a><\/p>\n

If you need to remove an IP address type ip address del 10.10.10.50\/24 dev eth0<\/i><\/b>or ifconfig eth0 delete 10.10.10.50.<\/i><\/b><\/span><\/p>\n

The default route\/gateway <\/i>address can be configured by typing the following command:<\/span><\/p>\n

route add default gw 10.10.10.1<\/i> o<\/b>r ip route add default via 10.10.10.1<\/i><\/b><\/span><\/p>\n

\"route<\/a><\/p>\n

Once the network parameters have been configured, we\u2019ll need to enable<\/i> the network interface by typing ifconfig eth0 up<\/i><\/b><\/span><\/p>\n

\"ifconfig<\/a><\/p>\n

To disable<\/i> a network interface, type ifconfig eth 0 down<\/i><\/b><\/span><\/p>\n

We\u2019ll need to add the DNS servers<\/i> used by our DHCP machine. Navigate to \/etc\/resolv.conf <\/i>and edit this file using your favorite editor. Once you\u2019ve opened the file, type in the following:<\/span><\/p>\n

nameserver DNS_SERVER_IP_ADDRESS<\/i> <\/b><\/span><\/p>\n

Add one entry per line for each DNS server\u2019s IP address<\/span><\/p>\n

\"\/etc\/resolve.conf\"<\/a><\/p>\n

SERVER CONFIGURATION<\/i><\/b><\/span><\/h2>\n

Now you should be able to ping any website and we are ready to install the DHCP service. There are several things that you\u2019ll need to know before we can proceed with the installation:<\/span><\/p>\n