Learn the DHCP series (vii) lease, release

This section focuses on DHCP IP address leases, release issues.

When a DHCP client acquires an IP address, it does not mean that the address can be used permanently, but rather has a usage term, which we call the lease term in DHCP, which is calculated by default from the time the client successfully acquires it, and pushes it back for another 8 days. In fact, apart from this 8-day period, within the valid lease period, there are two points of time, fourth and seventh days, that is, half of the lease and 7/8 of the lease. These three points are reflected in the DHCP Offer packet. The following figure:

The Marked red box in the above figure is three points in time.

Let's try to make an analogy. If the client successfully obtains an IP address on January 1 0 o'clock, the lease information is visible on DHCP Manager, and the corresponding lease expiration date is January 9 0 o'clock. The date is half of the default lease period, which is the fourth day. The client sends the DHCP server A

DHCP request packet, which is intended to ask for updates to its lease. If the DHCP server is normal and appropriate for this request, a packet of DHCP ACK is returned, which means that the renewal is successful. For example, January 5, the client to renew the application, when the DHCP server is normal, the client's IP expiration time will be extended to January 13, because he is the application in number 5th, to determine whether the renewal and expiration of the DHCP server on the time is whichever. I'll show you the time of the lease calculation in the form of drawing, as shown below: