DHCP

What is DHCP

Dynamic Host Configuration Protocol!!!! Provides automatic solution for ip address assignment and management. Used to configure IP addresses and subnetmask, default gatway, DNS Name Servers, Time Servers..

How does the DHCP lease process work?

Client requests an ip address by broadcasting a DHCP discover message to the local subnet(UPD). If a DHCP server responds, it sends an offer message including the ip address and configuration information. If no DHCP server responds two approaches: 1. if ip auto-config is enable the client will setup an ip address for itself 2. It resends a DHCPdiscover message (4 times every 5 min) until it receives an offer from a DHCP server. Once this is done the client sends a acceptance by selecting the offered addres and replying with a DHCP request message. The DHCP server notes the assignment and sends a DHCPAck message approving the lease. The client then configures the devices TCP/IP settings.

How does DHCP work

Client server based, including an IP address database, address leasing, and management is done by the server not the client. Using the BOOTP protocol and UDP port 67 for server and UDP port 68 for clients BASIC PROCESS Client requests and IP lease, Server sends back ip least offers, client makes an ip lease selection, and then the server sends a lease aknowledgement

Lease Renewal

DHCP Client s automatically renew their address lease when 1/2 of the lease time has expired, if the renewal is not completed it tries again at 3/4 of the lease duration, if it still cannot it tries again at 7/8 of the lease duration, and if it cannot do it at all it will have to renew the ip address when the lease expires

Ipconfig commands

Ipconfig /all (shows all detailed information) ipconfig /release (releases ip address) ip config /renew renews ip address

Complications across subnets

To use DHCP across subnets the router must be configures to forward DHCP requests or there must be a relay agent on the subnet ( this relay agent communicates directly with the DHCP server and acts as a proxy to the client and relays all messages from the client to the server and visa versa

Why DHCP

reduces manual configuration, reduces errors, ip address loss, reduces issues with mobile devices