ccna4 -Chapter7 : IP addressing services

provides IP addresses to clients

manual allocation: the adminstrator assigns a pre-allocated IP address to the client and DHCP only communicates the address to the device.

automatic allocation : assigns a static IP address permanently to a device.

dynamic allocatin - dynamically assigns, leases an IP address from a pool of addressfor a limited period of itme chosen by the server.

the PC connects to the network with that leased IP address until the lease expires The host must contact the DHCP server periodically to extend the lease.

- discovery - broadcasts a DHCPDISCOVER message. this message finds DHCP servers on the network.

Offer- DHCP server finds an available adress to lease, creates an ARP entry consisting of MAC address of the requesting host and the leased IP address and transmits a binding offer with a DHCPOFFER message.
This message is unicast, including the L2 MAC address of the server.

DHCPRQUEST - clients sends a DHCPREQUEST message. This includes lease origination and lease renewal and verification. This message is in the form of a broadcast to inform the server and any other DHCP server about the accepted offer.

DHCPACK - the server verifies the lease information creates the new ARP etnry for the client lease and replies with a unicast DHCPACK message. this is a duplicate of dhcpoffer.

- UDP ports 67 and 68

67 & 68

-performance
-affects integrity of the packet
-ip tracability is lost
-initiating TCP connections can be disturbed.

allows an external user to reach a prviate address inside a NATed network.
-allows users on the internet to access internal network by using WAN port address and the matched external port number. When users send packets to the WAN ip address, the packet is forwarded to the internal servers from the router