DHCP - Dynamic Host Configuration Protocol Daemon
What DHCP Server can do?
1. Provides automatic configuration of IPv4 clients
- IPv4 address
- Subnet mask
- Default gateway
- DNS Server
- NTP Servers
- WINS Servers
2. Leases the addreses and related information based on predefined values:
- 1 day
- 1 week
- 1 month
3. DHCP uses UDP protocol and layer-2 information to request/assign addresses
4. DHCP Process - DORA
- Discovery - client broadcasts on the local subnet for a DHCP server
- Offer - returned by the DHCP server
- Request - formal address request by client
- Acknowledgement/Acceptance - Acknowledgement occurrs
Note: DHCPD daemon records leases in: /var/lib/dhcpd/dhcpd.leases
Installing DHCP Server:
1. Install DHCP server
#yum -y install dhcp
2. Configure: /etc/dhcpd.conf - primary config file.
Look at sample dhcp configuration file below for the details:
ddns-update-style interim;
ignore client-updates;
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.10 192.168.1.250; # Range of IP addresses to be issued to DHCP clients
option subnet-mask 255.255.255.0; # Default subnet mask to be used by DHCP clients
option broadcast-address 192.168.1.255; # Default broadcastaddress to be used by DHCP clients
option routers 192.168.1.1; # Default gateway to be used by DHCP clients
option domain-name "your-domain.com";
option domain-name-servers 50.145.43.254, 50.145.43.253; # Default DNS to be used by DHCP clients
option netbios-name-servers 192.168.1.200; # Specify a WINS server for Windows clients. Its Optional.
default-lease-time 21600; # Amount of time in seconds that a client may keep the IP address
max-lease-time 43200;
option time-offset -18000; # Eastern Standard Time
option ntp-servers 192.168.1.1; # Default NTP server to be used by DHCP clients
# We want the nameserver "mailsrv2" to appear at a fixed address.
# Name server with this specified MAC address will recieve this IP.
host mailsrv2 {
next-server mailsrv2.your-domain.com;
hardware ethernet 00:12:f3:d0:f5:93;
fixed-address 50.145.43.254;
}
host laser-printer-hp1 {
hardware ethernet 06:20:2e:4f:b3:88;
fixed-address 192.168.1.150;
}
}
Note: DHCP can be configured with more and more options. I have specified very limited only here. refer the man page for details.
3. Set service up to start when system boots
#chkconfig dhcpd on - 2345
4. Start DHCP service:
#service dhcpd start
How to Setup DHCP reservations?
- Requires the MAC address of the client (00:0D:69:A5:15:94)
- Requires the 'fixed-address' - IPv4 address to map to the MAC address
- Optional 'option-*' are supported between host { } block
- service dhcpd restart - restart to effect changes
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