DHCP is a protocol that dynamically assigns IP addresses and other network configuration parameters to clients on a network. It allows for centralized management of IP addresses and helps conserve IP addresses. A DHCP server manages pools of IP addresses and related configurations to hand out to DHCP client software installed on other devices on the network to automatically obtain IP addresses and other networking settings as needed. A DHCP relay agent can help extend DHCP services to remote subnets that don't have direct access to the DHCP server.

1. DHCP SERVER CONFIGURATION

2. DHCP - INTRODUCTION
 DHCP was created by the Dynamic Host Configuration Working Group of the Internet
Engineering Task Force(IETF)
 Runs over UDP
 Utilizing ports:
 67 – connections to server
 68 – connections to client
 Used for Dynamic configuration
 Uses client–server model
 Extension of BOOTP

3. OBJECTIVE OF DHCP
 It temporarily binds IP address & other configuration parameters to DHCP client & provides
framework for passing configuration information to hosts
 It was designed to provide computers with temporary address
 It is well adapted to situation where hosts move from one location to another or are routinely
connected and disconnected
 Thus DHCP is mainly used to simplify the installation & maintenance of networked
computers.

4. CHARACTERISTICS
 Centralized IP address administration
 Backward compatible with BOOTP
 Supports multiple servers
 Provides dynamic assignment
 Allows static assignment
 Doesn’t interact with domain name service (DNS)

5. SOFTWARE ELEMENTS
 Client Software
 Installed in client Machines
 To handle broadcast requests
 For automatic IP acquisition and acquiring other configuration
 Server Software
 Installed in server machines
 Designated to respond to client requests for ip address
 Manage pools of IP addresses and related configuration

6. SOFTWARE ELEMENTS
 Relay Agent Software
 DHCP clients broadcasts requests onto local n/w
 Routers block broadcasts to outer network which means responses
from the DHCP servers must come from same network
 DHCP relay agents intercepts IP address requests
 repackages the requests
 rebroadcasts them as unicast messages to DHCP servers with known
addresses of other network
 DHCP servers sends its reply to relay agent which in turn forwards
them to client requesting the IP address

7. DHCP SERVER INSTALLATION

8. BASIC DHCP CONFIGURATION
 By default, DHCP server configuration does not include any subnets on which DHCP server should lease
IP addresses.
 It depends on your Linux system you may get the following error message when you attempt to start
DHCP with default dhcpd.conf configuration file.
 Your server may be connected to multiple network subnets.

9. BASIC DHCP CONFIGURATION
 simplest example of DHCP configuration file:
 Alter the above code with your subnet and insert it into /etc/dhcp/dhcpd.conf. When ready, restart your
DHCP server with ( restart command may vary ) :

10. DHCP DATABASES
 DHCP server uses 2 databases :
 One database acquires IP addresses manually and binds them permanently to hardware
addresses similar to BOOTP
 Other database contains 1 or more blocks of IP addresses (address pools) that are
dynamically assigned to clients on FCFS basis i.e. assigning on demand.
 when host no longer needs the IP address, it is released & returned

11. DHCP LEASE TIME MANAGEMENT
 DHCP issue a lease for a dynamic IP address that expires at the end of lease time
 After 1⁄2 the lease time,client can renew the lease time
 Once lease has expired the client must either stop using the IP address or acquire a new IP address
 If more than 1 DHCP server, each may offer an IP address to client & client can select the best offer.

12. 3 TYPES OF ADDRESS LEASES
 Manual Lease : Network manager explicitly assigns all IP addresses
 Automatic Lease : DHCP server permanently assigns specific IP address and dynamically
assigns the rest
 Dynamic Lease : DHCP server dynamically assigns IP addresses for a specific period of time
when permanent address is not required

13. DHCP DEFAULT AND MAX LEASE TIME
 At this point we can add few additional settings to our DHCP configuration :
 Default-lease-time
 Max –lease-time

14. DEFINE DNS SERVER

15. SET DEFAULT GATEWAY

16. HOST SPECIFIC CONFIGURATION

17. CLIENT NETWORK SETTINGS TO USE DHCP
 To configure your client to use a DHCP on a network interface linux systems enter a following lines in
your /etc/network/interfaces file:

18. CONFIGURING DHCP RELAY AGENT
 If your DHCP server does not have an access to some particular subnet it does not mean that it
cannot provide its services there. To make this work a DHCP relay agent needs to be configured on a
remote subnet which forwards all request to a specified DHCP server and distant subnet. First install
DHCP relay agent:
 Then create a configuration file /etc/default/isc-dhcp-relay with two lines:
 The above config file will instruct DHCP relay agent to listen on eth0 interface for a DHCP client
requests and forward them to a DHCP server on an IP address 192.168.5.5.

19. USAGE SCENARIOS
 There are four key DHCP usage scenarios:
 Initial Client Connection: the client requests from the DHCP server an IP address and other
parameter values for accessing network services
 IP Usage Extension: the client contacts the DHCP server to extend usage of its current IP
address
 Client Connection After Reboot: the client contacts the DHCP server for confirmation that it
can use the same IP address being used before reboot
 Client Disconnection: the client requests the DHCP server to release its IP address.

20. DHCP SECURITY
 DHCP is an unauthenticated protocol
 When connecting to a network, the user is not required to provide credentials in order to
obtain a lease
 Also the server is also not the authenticated one
 Malicious users with physical access to the DHCP-enabled network can start a denial-of-
service attack on DHCP servers by requesting many leases from the server, thereby
reducing the number of leases that are available to other DHCP clients

21. THANK YOU!