Updating Ip Address Lease; Dhcp Packet Format - H3C S7500 Series Operation Manual

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Operation Manual – DHCP

H3C S7500 Series Ethernet Switches

The IP addresses offered by other DHCP servers (if any) are not used by the DHCP

client and are still available to other clients.

1.2.3 Updating IP Address Lease

After a DHCP server dynamically assigns an IP address to a DHCP client, the IP

address keeps valid only within a specified lease time and will be reclaimed by the

DHCP server when the lease expires. If the DHCP client wants to use the IP address

for a longer time, it must update the IP lease.

By default, a DHCP client updates its IP address lease automatically by unicasting a

DHCP-REQUEST packet to the DHCP server when half of the lease time elapses.

The DHCP server responds with a DHCP-ACK packet to notify the DHCP client of a

new IP lease if the server can assign the same IP address to the client. Otherwise, the

DHCP server responds with a DHCP-NAK packet to notify the DHCP client that the IP

address will be reclaimed when the lease time expires.

If the DHCP client fails to update its IP address lease when half of the lease time

elapses, it will update its IP address lease by broadcasting a DHCP-REQUEST

packet to the DHCP server again when seven-eighths of the lease time elapses. The

DHCP server performs the same operations as those described in the previous

DHCP has eight types of packets. They have the same format, but the values of some

fields in the packets are different. The DHCP packet format is based on that of the

BOOTP packets. The following table describes the packet format (the number in the

brackets indicates the field length, in bytes):

Chapter 1 DHCP Overview

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