DHCP

DHCP

• 1.
  Dynamic Host Configuration Protocol
• 2.
  DHCP  A hostneed an IP Address and some other piece of information (subnet mask, gateway address, etc…) to send the packets.  Normally this information’s are provided by the system administrator and configure in manually.  But for a large network it is complex and error prone. So automatic configuration method is used.  Automatic configuration is provided by DHCP.  It needs a DHCP server to provide the information dynamically.  DHCP Server – It is a central repository for host configuration details.
• 3.
  DHCP Steps,  A newlybooted or attached host sends a “DHCP DISCOVER” message to special IP Address 255.255.255.255 (Broadcast Address).  DHCP relay receives this request and unicast that request to the DHCP server.  DHCP relay – It contains the IP address of DHCP Server.  DHCP server sends back the response to the requesting client.
• 4.
  DHCP  DHCP dynamicallyassigns IP address to hosts. But host cannot keep addresses indefinitely.  Thus DHCP allows addresses to be “leased” for some period of time. Once the lease expires, client needs to renew the IP Address. Advantages,  Scaling of network management  Improves manageability of a network.
• 5.
  Unicast Broadcast Host DHCP Relay Other NetworksDHCP Server
• 7.
  DHCP  Operation Code(8 bit) – specifies whether the message is request (1) / response (2).  Hardware Type (8 bit)–Specifies the type of hardware used for local network (value 1 – Ethernet).  Hardware Address Length (8 bit)–Specifies the length of the hardware address.
• 8.
  DHCP  Hops (8bit) – Used to control the DHCP request message by DHCP relay.  Transaction Identifier (32 bit) – XID - A 32-bit identification field generated by the client, to allow it to match up the request with replies received from DHCP servers.
• 9.
  DHCP  Seconds (16bit) -number of seconds elapsed since a client began an attempt to acquire or renew a lease.  Flag (16 bit) –B bit is set to 1 to represent the broadcast message. Other bits are set to Zero.  Client IP Address - The client puts its own current IP address in this field if and only if it has a valid IP address while in the renewing state.
• 10.
  DHCP  Your IPAddress - The IP address that the server is assigning to the client.  Server IP Address –Address of the DHCP server.  CHAddr –Client Hardware Address - The hardware address of the client, which is used for identification and communication.  SName –Server Name – Name of the DHCP server, provided by the server during the response.