1. Sasken Confidential © 2007 Sasken Communication Technologies Host Configuration Protocol By Manikanta Velaga

2. 2 © 2007 Sasken Communication Technologies Topics RARP BOOTP DHCP

3. 3 © 2007 Sasken Communication Technologies RARP[Reverse Address Resolution Protocol]  This protocol translates a physical address[MAC Address] to IP address.  By using this protocol a physical machine in a LAN can send a request to learn its IP address from the Gateway’s ARP table or cache.  A network administrator manually creates a table in a LAN’s Gateway/Router that maps the physical addresses to corresponding IP addresses.  When a machine is booting its RARP client sends a request for IP address to RARP server on the Gateway/Router. If the entry has already been setup in the Gateway’s table, RARP server of the Gateway will return the machine’s IP address. How it works? Disadvantages  RARP server must be present in each network.  Admin manually has to create the table and table entries in the LAN’s Gateway/Router.  RARP server does not provide any other information like IP address of the Gateway and IP address of the DNS server.

4. 4 © 2007 Sasken Communication Technologies BOOTP  BOOTP server can be run in anywhere in the internet.  It provides other information along with IP address.  Network administrator manually creates a table and mappings.  These mappings are static and fixed and they can’t be changed dynamically until changed by network administrator.  When a client requests its IP address, the BOOTP server searches for an entry that matches the physical address of the client and it returns of the corresponding IP address. How it works? Disadvantages  There are some situations, in which a host wants a temporary IP address to be used for some time.  Admin has to create the table and table entries manually, i.e this is a static configuration protocol, it can not handle dynamic situations.

5. 5 © 2007 Sasken Communication Technologies DHCP  It is a client server protocol designed to provide IP address dynamically and necessary information to a host for communicating with other network.  DHCP client sends a request to DHCP server while host’s booting process, when a DHCP server receives a request from a client; it selects an IP address from a pool of addresses present in its database and offers it to client. If the client accepts the offer, that IP address is given to client for a period of time.  DHCP Server can be run in the same network or it can be on some other network.  When DHCP Server is running on other network, “DHCP Relay Agent” acts as a mediator between DHCP Client and DHCP Server to transfer requests and responses.  DHCP provides extra information along with IP address: 1)Subnet mask of the computer, 2)IP address of the Gateway/Router, 3)IP address of the DNS server. How it works?

6. 6 © 2007 Sasken Communication Technologies DHCPSERVER1DHCPSERVER1 DHCPCLIENTDHCPCLIENT DHCP DISCOVER--> <--DHCP OFFER <--DHCP ACK DHCP REQUEST--> DHCPSERVER2DHCPSERVER2 ROUTERROUTER DHCP DISCOVER --> <-DHCP OFFER DHCP REQUEST--> DHCP DISCOVER--> <--DHCP OFFER DHCP REQUEST--> DHCP Relay agent is running on router. DHCP REQUEST--> <--DHCP ACK

7. 7 © 2007 Sasken Communication Technologies Operation Code 1 Byte1Mandatory Hardware Type 1 Byte1Mandatory Hardware Length 1 Byte6Mandatory Hop Count 1 Byte0Mandatory Transaction ID 4 BytesTo be generated randomly and filled. Mandatory Number of Seconds 2 Bytes0 /*To be find out and filled*/Mandatory Flags2 Bytes0 /*Left most bit should be 1*/Mandatory Client IP Address4 Bytes0Mandatory Your IP Address4 Bytes0Mandatory Server IP Address4 Bytes0Mandatory Gateway IP Address4 Bytes0Mandatory Client Hardware Address16 BytesTo be find out and filledMandatory Server Name64 Bytes0Mandatory Boot File Name128 Bytes0Mandatory MagicCookie4 Bytes99.130.83.99Mandatory Tag1 Byte53 Length1 Byte1 DHCPMessageType1 Byte1Optional Tag1 Byte55 Length1 Byte4 Parameter Request List4 Byte01,28,03,15[0x01, 0x1C, 0x03, 0x0F] Optional EndOfList1 Byte255 Content of the DHCPDISCOVER message Field Name Length Value Comments

8. 8 © 2007 Sasken Communication Technologies End of the presentation