O Ciclo de Vida de Locação do DCHP
The use of dynamic address allocation in DHCP means a whole new way of thinking about IP Addresses.
- A client no longer owns an IP Address, but rather leases it.
- This means that when a client machine is set to use DHCP dynamic addressing, it can never assume that it has an IP Address on a permanent basis.
- Each time it powers up, it must engage in communications with a DHCP server to begin or confirm the lease of an IP Address.
- It also must perform other activities over time to manage this lease and possibly terminate it.
Typically, a client can keep its IP Address for several days (or whatever you configure). When half the lease time expires, the client attempts to renew its lease for the IP Address. After a client obtains the lease for an IP Address, it attempts to keep the lease by renewing it over and over. If unsuccessful, the client simply must get a new IP Address lease.
DHCP leases follow a "life cycle", which generally consists of the following phases:
- Allocation: A client begins with no active lease, and hence, no DHCP-assigned IP Address. It acquires a lease through a process of allocation.
- Reallocation: If a client already has an IP Address from an existing lease, then when it reboots or starts up after being shut down, it will contact the DHCP server that granted it the lease to confirm the lease and acquire operating parameters. It is similar to the full allocation process but shorter.
- Normal Operation: Once a lease is active, the client functions normally, using its assigned IP Address and other parameters during the "main part" of the lease. The client is said to be bound to the lease and the address.
- Renewal: After a certain portion of the lease time has expired, the client will attempt to contact the server that initially granted the lease, to renew the lease so it can keep using its IP Address.
- Rebinding: If renewal with the original leasing server fails (because, for example, the server has been taken offline), then the client will try to rebind to any active DHCP server, trying to extend its current lease with any server that will allow it to do so.
- Release: The client may decide at any time that it no longer wishes to use the IP Address it was assigned, and may terminate the lease, releasing the IP Address. This may be done if a device is moving to a different network, for example.
This diagram illustrates the DHCP life cycle using an example that spans three leases:
- The initial lease has a duration of eight days and begins at Day 0.
- The T1 and T2 timers are set for 4 days and 7 days respectively.
- When the T1 timer expires the client enters the renewal period, and successfully renews at Day 5 with a new 8-day lease.
- When the second lease T1 timer expires, the client is unable to renew with the original server.
- It enters the rebinding period when its T2 timer goes off, and is granted a renewed 8-day lease with a different server.
- Three days into this lease it is moved to a different network and no longer needs the leased IP Address, and voluntarily releases it.
Fonte: www.tcpipguide.com