DHCP Server Configuration on Linux 5

DHCP Server Configuration

Introduction:-

Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses and other network configuration information (subnetmask, broadcast address, etc) to computers on a network. A client configured for DHCP will send out a broadcast request to the DHCP server requesting an address. The DHCP server will then issue a "lease" and assign it to that client. The time period of a valid lease can be specified on the server.

• DHCP assignment:

• Lease Request: Client broadcasts request to DHCP server with a source address of 0.0.0.0 and a destination address of 255.255.255.255. The request includes the MAC address which is used to direct the reply.
• IP lease offer: DHCP server replies with an IP address, subnet mask, network gateway, name of the domain, name servers, duration of the lease and the IP address of the DHCP server.
• Lease Selection: Client recieves offer and broadcasts to DHCP servers that will accept given offer so that other DHCP server need not make an offer.
• The DHCP server then sends an ack to the client. The client is configured to use TCP/IP.
• Lease Renewal: When half of the lease time has expired, the client will issue a new request to the DHCP server.

Requirement:-

·         Package = dhcp (dhcp-3.0.5-21.el5, dhcp-devel-3.0.5-21.el5, dhcpv6-client-1.0.10-17.el5, dhclient-3.0.5-21.el5)

·         Service = dhcpd

• Port No. = 67
• Configuration File = /etc/dhcpd.conf

Per quest:-

• Configure IP = 192.168.100.250
• Configure Hostname = dhcp
• Firewall must be disabled.

Step-1:  To check dhcp  rpm package is installed or not by following this command:

                       

(if installed then it will show dhcp packages)

[root@dhcp ~]# rpm -qa | grep –i dhcp*    or

[root@dhcp ~]#  rpm –qa dhcp*

dhcp-3.0.5-21.el5

dhcp-devel-3.0.5-21.el5

libdhcp-devel-1.20-10.el5

dhcpv6-client-1.0.10-17.el5

libdhcp-1.20-10.el5

libdhcp4client-3.0.5-21.el5

libdhcp6client-devel-1.0.10-17.el5

libdhcp4client-devel-3.0.5-21.el5

dhclient-3.0.5-21.el5

           If not installed, then installed the packages using  Yum command:

[root@dhcp ~]# Yum Install dhcp* lib*

Step-2: Check and Configure the Network Card:

[root@dhcp ~]# vi /etc/sysconfig/network-scripts/ifcfg-eth0

(Original File):

#Broadcom Corporation Net link BCM57875 Gigabyte Ethernet PCI Express

DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=00:0C:29: EB: B2: CA
ONBOOT=yes

(Modified File):

#Broadcom Corporation Net link BCM57875 Gigabyte Ethernet PCI Express

DEVICE=eth0

BOOTPROTO=none

HWADDR=00:0c:29:26:56:fc

ONBOOT=yes

NETMASK=255.255.255.0

IPADDR=192.168.100.250

TYPE=Ethernet

Step-3:  After complete the NIC configure you have to change the host name by following this command:

[root@dhcp ~]# vi /etc/sysconfig/network

(Original File):

NETWORKING=yes

NETWORKING_IPV6=no

HOSTNAME=localhost.localdomain

(Modified File):

NETWORKING=yes

NETWORKING_IPV6=no

HOSTNAME=dhcp

Step-4:  Copy & Rename the DHCP configuration file & Change the permission by following this command:

[root@dhcp ~]# cd /usr/share/doc/dhcp-3.0.5/

[root@dhcp dhcp-3.0.5]# cp dhcpd.conf.sample  /etc/dhcpd.conf

Step-5: Edit the dhcpd.conf file as follows:

[root@dhcp ~]# vi /etc/dhcpd.conf

(Original File):

ddns-update-style interim;

ignore client-updates;

subnet 192.168.0.0 netmask 255.255.255.0 {

# --- default gateway

      option routers                192.168.0.1;

      option subnet-mask            255.255.255.0;

      option nis-domain       "domain.org";

      option domain-name            "domain.org";

      option domain-name-servers    192.168.1.1;

      option time-offset            -18000;     # Eastern Standard Time

#     option ntp-servers            192.168.1.1;

#     option netbios-name-servers   192.168.1.1;

# --- Selects point-to-point node (default is hybrid). Don't change this unless

# -- you understand Netbios very well

#     option netbios-node-type 2;

      range dynamic-bootp 192.168.0.128 192.168.0.254;

      default-lease-time 21600;

      max-lease-time 43200;

      # we want the nameserver to appear at a fixed address

      host ns {

            next-server marvin.redhat.com;

            hardware ethernet 12:34:56:78:AB:CD;

            fixed-address 207.175.42.254;

      }

}

(Modified File):

ddns-update-style interim;

ignore client-updates;

subnet 192.168.100.0 netmask 255.255.255.0 {

# --- default gateway

        option routers                  192.168.100.254;

        option subnet-mask              255.255.255.0;

        option nis-domain               "domain.org";

        option domain-name              "gsnone.com";

        option domain-name-servers      ns1.gsnone.com;

        option time-offset              -18000; # Eastern Standard Time

#       option ntp-servers              192.168.1.1;

#       option netbios-name-servers     192.168.1.1;

# --- Selects point-to-point node (default is hybrid). Don't change this unless

# -- you understand Netbios very well

#       option netbios-node-type 2;

        allow booting;

        allow bootp;

#       option-128 code 128 = string;

#       option-129 code 129 = text;

        next-server 192.168.100.250;

        filename "pxelinux.0";

        range dynamic-bootp 192.168.100.151 192.168.100.199;

        default-lease-time 21600;

        max-lease-time 43200;

        # we want the nameserver to appear at a fixed address

        host ns {

                next-server marvin.redhat.com;

                hardware ethernet 12:34:56:78:AB:CD;

                fixed-address 207.175.42.254;

        }

}

Details Explanation

01	ddns-update-style interim;       # Required for dhcp 3.0+ / Red Hat 8.0+
02	ignore client-updates;

03
04	subnet 192.168.1.0 netmask 255.255.255.0 {

05
06	range 192.168.1.128 192.168.1.254;    # Range of IP addresses to be issued to DHCP clients

07	option subnet-mask              255.255.255.0;    # Default subnet mask to be used by DHCP clients
08	option broadcast-address        192.168.1.255;    # Default broadcastaddress to be used by DHCP clients

09	option routers                  192.168.1.1;      # Default gateway to be used by DHCP clients
10	option domain-name              "your-domain.org";

11	option domain-name-servers      40.175.42.254, 40.175.42.253;           # Default DNS to be used by DHCP clients
12	option netbios-name-servers     192.168.1.100;    # Specify a WINS server for MS/Windows clients.

13	# (Optional. Specify if used on your network)
14

15	#         DHCP requests are not forwarded. Applies when there is more than one ethernet device and forwarding is configured.
16	#       option ipforwarding off;

17
18	default-lease-time 21600;         # Amount of time in seconds that a client may keep the IP address

19	max-lease-time 43200;
20

21	option time-offset              -18000;              # Eastern Standard Time
22	#       option ntp-servers              192.168.1.1;         # Default NTP server to be used by DHCP clients

23	#       option netbios-name-servers     192.168.1.1;
24	# --- Selects point-to-point node (default is hybrid). Don't change this unless you understand Netbios very well

25	#       option netbios-node-type 2;
26

27	# We want the nameserver "ns2" to appear at a fixed address.
28	# Name server with this specified MAC address will recieve this IP.

29
30	host ns2 {

31	next-server ns2.your-domain.com;
32	hardware ethernet 00:02:c3:d0:e5:83;

33	fixed-address 40.175.42.254;
34	}

35
36	# Laser printer obtains IP address via DHCP. This assures that the

37	# printer with this MAC address will get this IP address every time.
38

39	host laser-printer-lex1 {
40	hardware ethernet 08:00:2b:4c:a3:82;

41	fixed-address 192.168.1.120;
42	}

43

}

Step-6:  Create a dhcp.leases file that the DHCP server grants to the DHCP client to use a particular IP   address. If it does not exist dhcp server will fail to provide IP address for dhcp cient.

[root@dhcp ~]# touch /var/lib/dhcpd/dhcpd.leases

[root@dhcp ~]# service network restart

[root@dhcp ~]# service dhcpd restart

Step-7:   Client Configuration for using DHCP.

Linux Client

[root@dhcp ~]# vi /etc/sysconfig/network-scripts/ifcfg-eth0

#Broadcom Corporation Net link BCM57875 Gigabyte Ethernet PCI Express

DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=00:0C:29: EB: B2: CA
ONBOOT=yes

TYPE=Ethernet

Windows Client

From NIC Properties =>> set Obtain an IP Address Automatically

Step-7:   Renewing IP Address

Renew an IP Address in Linux

The -r flag explicitly releases the current lease, and once the lease has been released, the client exits. For example, open terminal and type the command:

[root@dhcp ~]# dhclient –r

Now obtain fresh IP:

[root@client1 ~]# dhclient

Or you can put the two commands on a single line:

[rnbsp; oot@client1 ~]# dhclient -r; dhclient

There is no need to restart network service. Above command should work with any Linux distro such as RHEL, Fedora, and others. On a related note you can also try out the following commands:

[root@client1 ~]# ifdown eth0
[root@client1 ~]# ifup eth0
[root@client1 ~]# /etc/init.d/network restart

Renew an IP Address in Windows

Open Command Prompt → Then Type The following command

C:\Documents and Settings\Administrator> Ipconfig  /release

C:\Documents and Settings\Administrator> Ipconfig  /renew

C:\Documents and Settings\Administrator> Ipconfig  /all