Qtech QSW-2900-24T-AC [108/209] Dhcp packet format

6-106
packet.
4) Acknowledge: Upon receiving the DHCP-REQUEST packet, the DHCP server returns a DHCP-ACK
packet to the DHCP client to confirm the assignment of the IP address to the client, or returns a DHCP-NAK packet
to refuse the assignment of the IP address to the client. When the client receives the DHCP-ACK packet, it
broadcasts an ARP packet with the assigned IP address as the destination address to detect the assigned IP address,
and uses the IP address only if it does not receive any response within a specified period.
& Note:
The IP addresses offered by other DHCP servers (if any) are not used by the DHCP client
and are still available to other clients.
6.3.3 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 section.
6.4 DHCP Packet Format
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):

Содержание

Скачать
Случайные обсуждения