What : DHCP (DYNAMIC HOST CONFIGURATION PROTOCOL), as name suggests, dynamically provide IP address to the host
DHCP supports three types of mechanism, whIle providing IP
Automatic allocation—DHCP assigns a permanent IP address to a client.
Dynamic allocation—DHCP assigns an IP address to a client for a limited period of time
Manual allocation—The network administrator assigns an IP address to a client and DHCP is used simply to convey the assigned address to the client.
DHCP is based on the Client/ Server model
Assigns and manages IP addresses from specified address pools within the router to DHCP clients.
DHCP Server cannot satisfy a DHCP request from its own database, it can forward the request to one or more secondary DHCP Servers defined network administrator
DHCP SERVER/CLIENT COMMUNICATION
DHCPDISCOVER: search for the DHCP server
DHCPOFFER: DHCP Server offers configuration parameters (such as an IP address, a , a domain name, and a lease for the IP address) to the client
// A DHCP client may receive offers from multiple DHCP Servers and can accept any one of the offers; however, the client usually accepts the first offer it receives. Additionally, the offer from the DHCP Server is not a guarantee that the IP address will be allocated to the client //
DHCPREQUEST: DHCP client sends this to all the DHCP servers, so that all remaining DHCP servers can reclaim their IP
DHCPACK: DHCP Server confirms that the IP address has been allocated to the client
DHCP SERVER IP ALLOCATION PROCESS
DHCPDISCOVER packet is examined, which contains a feild, called giaddr feild
Client is not directly connected to DHCP server
Then, giaddr field= non-zero= some IP address
DHCP server matches availiable DHCP pools with the IP address present in the giaddr feild, both must belong to the same subnet
Client is directly connected to DHCP server
Then, giaddr field= zero
DHCP server matches availiable DHCP pools with IP address configured on the receiving interface, both must belong to the same subnet
DHCP RELAY AGENT
What: A DHCP relay agent is any host that forwards DHCP packets between clients and servers. Relay agents are used to forward requests and replies between clients and servers when they are not on the same physical subnet. Relay agent forwarding is distinct from the normal forwarding of an IP router, where IP datagrams are switched between networks somewhat transparently. Relay agents receive DHCP messages and then generate a new DHCP message to send out on another interface.