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
- 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
- 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!