DHCP stands for Dynamic Host Configuration Protocol. DHCP Servers is used to assign an IP to the computers on a network. DHCP was first introduced in RFC 1531 in October 1993. The connected computers of a network must be configured before the starting of communication with all other computers on the network. DHP servers facilitate the clients with automatic option and save user time because DHCP server configured all computers used in a network automatically. DHCP servers also offer a central database for continuing track of computers that have been attached to the network and also avoid more than one computer from by accident being configured with the similar IP address. IPv4 and IPv6 are DHCP versions which are available in market having same performance and name. Dynamic Host Configuration Protocol makes uses of two ports consigned by LANA for BOOTP. DHCP Servers use 67/udp for the sending of data to server and 68/udp for client. Whole operation performed in four stages such as IP lease, request, lease offer, and IP discovery.
When client and server use the same subnet they can converse through UDP broadcast, but if they use different subnet than IP request and discovery messages sent through UDP and IP leas and leas offer messages sent through unicast. Dynamic Host Configuration Protocol (DHCP) assign an IP to network when following condition happen
- A user powers on a computer with a Dynamic Host Configuration Protocol (DHCP) client.
- Then client computer send a DHCPDISCOVER to answer and router direct the DHCPDISCOVER packet to the specified DHCP server.
- After receiving request called DHCPDISCOVER server decide as suitable address to grant to the client.
- Then server reserves it as temporary for the client and sends back to client with address information. Server is also responsible to configure NTP servers, DNS servers and WINS servers etc.
- After above process client sends a DHCP REQUEST packet let to tell the server that it is going to use the address.
- Then server sends a DHCPACK packet for confirmation purpose that client ha been given a let on the address for specified time.
DHCP server methods for allocating IP-addresses
Dynamic Host Configuration Protocol (DHCP server) uses three method of allocating IP addresses as followings
Dynamic DHCP allocation
Through dynamic DHCP allocation network supervisor consign a variety of IP addresses to DHCP server. Every client has its IP software for the configuration to ask for an IP address since the DHCP server initializing. The request process uses lease perception with a specified and fixed time period which permits the DHCP server to retrieve IP addresses that neither are nor improved.
Automatic DHCP allocation
Automatic DHCP allocation is just like a dynamic allocation because in automatic allocation the server assigns a free IP address o client everlastingly from the given collection provided by administrator. But in automatic DHCP allocation the server remains the history of past therefore it can prefer to assign the same IP address to client that previously had.
Static DHCP allocation
Static DHCP allocation feature is not supported by all devices. In static allocation DHCP server permit an IP address from the desk with the match up of MAC address and IP address specified by network administrator .Those clients who are applied for with a MAC address specified in table will be allocated an IP address.
DHCP Servers includes no security therefore potentially susceptible to two kind of assault.
Unauthorized DHCP Servers
Because of lack of security a client cannot identify the server and unauthorized server may respond to client request and as a result a hacker may take control the DHCP procedure to configure clients to use a malevolent DNS server or router.
Unauthorized DHCP Clients
By camouflaged as a lawful client, an unauthorized client can achieve entrance to network configuration and an IP address on a network it should or else not be permissible to employ. It is probable for an assailant to tire out the pool of accessible IP addresses, troublesome normal network activity