- The main purpose
- Why?
- Who can be a DHCP server?
- Router
- Core Switch
- Firewall
- Server
- Which kind of problems solves DHCP?
- Duplicate IP Address
- Human Error
- Complex administration
- DHCP supports three mechanisms for IP address allocation:
- Automatic allocation assigning a permanent IP Address to a host.
- Dynamic allocation assigned an IP address for a limited period of time.
- Manual Allocation where an administrator manually define which IP address assigned to the host.
- Manual allocations allows DHCP to be used to eliminate the error-prone process.
DHCP Messages
| DHCP Discover | Broadcast/ UDP messaged used to located a DHCP server. |
| DHCP Offer | Unicast Server responds with an offer of configuration. |
| DHCP request | Broadcast Client responds for: 1)To confirm that accepts one offer from one DHCP server declining others. 2)When was restarted and send a message request to confirm if he can use the last leased configurations. When the client was logging into the network before. 3)Extending the lease on a particular address. |
| DHCP ACK | Unicast Sent by DHCP Server to acknowledge the Request message. |
| DHCP NACK | Server declined the client's Request Message. |
| DHCP RELEASE | Client cancels the remaining lease |
| DHCP Inform Message | After a host has IP address and Mask sent this message to obtain gateway address and DNS addresses. |
| DHCP DECLINE | Sent by a client do inform the server the IP address is under use. |
Afterreceiving a DHCP Discover message each DHCP Server selects an unassigned IPAddress from the pool and sends a DHCP Offers message with the assigned IPAddress and others configurations. Ifmultiples DHCP servers offers the client accepts the first DHCP offers Messagereceived.
Three timers are set on the DHCP client.
| Release Renewal | At what time needs to renew the lease IP address. Default 50% of the lease time. |
| Rebinding timer | The time which will wait to have an answer from the DHCP server. Default 12.5% of the lease time. |
| Lease timer | Final timer in the expiration process. If the client doesn't receive an answer before the lease time expires the DHCP client must stop using the current IP Address immediately. And start a new DHCP DISCOVER. |
- The leased time by default is 1 day.
| Port | Server | Protocol |
| 67,68 | DHCP | UDP |
This post was last edited by DiegoXD at 2018-08-16 13:44.
