Protocol that is responsible for giving and removing IP Addresses.
Devices use this for obtaining dynamic IP Address
Conventionally seen on port udp/67 and udp/68.
It is recommended to disable DHCP to prevent unknown devices from entering the network. All known devices should have a static IP.
If you really need DHCP, allot a minimum of DHCP addresses
Dynamic Address Protocol
DISCOVER > OFFER > REQUEST > ACK (DORA)
- New device enters the network and notifies to the DHCP server
- DHCP server sends a Broadcast Frame containing all possible IP addresses device can have. These IP’s are given on a lease meaning they can expire if the device is unable to renew it automatically.
- The device picks one and notifies the DHCP server so that it may not be assigned again
- DHCP assigns the address and sends an acknowledgement reply
DHCP Reservation (Static IP)
The DHCP server can be configured so that it reserves a IP address for a MAC Address. Servers tend to want this.
Leasing
All IP addresses are leased and will be revoked unless renewed. By default this lease is 8 days 2 Timers will check if devices want renewed leases.
T1 Timer
- Checks at 50% of the lease time if the device wants to renew
T2 Timer
- Checks at 87.5% of the lease time if the device wants to renew
- Used for redundancy incase the DHCP goes down temporarily