14 DHCP Snooping Configuration
14.1 DHCP Snooping Overview
14.1.1 Understanding DHCP
The DHCP is widely used to dynamically allocate the reusable network resources, for
example, IP address. A typical IP acquisition process using DHCP is shown below:
Figure 14-1
The DHCP Client sends a DHCP DISCOVER broadcast packet to the DHCP Server. The
Client will send the DHCP DISCOVER again if it does not receive a response from the server
with a specified time.
After the DHCP Server receives DHCP DISCOVER packets, it allocates resources to the
Client (for example, IP address) according to the appropriate policy, and sends the DHCP
OFFER packets.
After receiving the DHCP OFFER packet, the DHCP Client sends a DHCP REQUEST for
obtaining the server lease, and notifies other servers that it has accepted this server for
address assignment.
After receiving the DHCP REQUEST packet, the server verifies whether the resource can be
distributed. If yes, it sends the DHCP ACK packet. If not, it sends the DHCP NAK packet.
Upon receiving the DHCP ACK packet, DHCP Client starts to use the resources assigned by
the server. If it receives DHCP NAK, then it will send the DHCP DISCOVER packet again.
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