Huawei Quidway S3900 Series User Manual

Operation Manual - DHCP
Quidway S3900 Series Ethernet Switches-Release 1510 Chapter 3 DHCP Relay Configuration
Huawei Technologies Proprietary
3-8
III. Configuring the dynamic user address entry updating function
When a DHCP client obtains an IP address from a DHCP server with the help of a
DHCP relay, the DHCP relay creates an entry (dynamic entry) in the user address
table to track the binding information about the IP address and MAC address of the
DHCP client. But as a DHCP relay does not process DHCP-RELEASE packets, which
are sent to DHCP servers by DHCP clients through unicast when the DHCP clients
release IP addresses, the user address entries maintained by the DHCP cannot be
updated in time. The dynamic user address entry updating function is developed to
resolve this problem.
The dynamic user address entry updating function works as follows: at regular
intervals, the DHCP relay sends a DHCP-REQUEST packet that carries the IP
address assigned to a DHCP client and its own bridge MAC address to the
corresponding DHCP server. If the DHCP server answers with a DHCP-ACK packet,
the IP address is available (it can be assigned again) and the DHCP relay ages out the
corresponding entry in the user address table. If the DHCP server answers with a
DHCP-NAK packet, the IP address is still in use (the lease is not expired) and the
DHCP relay remains the corresponding user address entry unchanged.
Table 3-6 Configure the dynamic user address entry updating function
Operation Command Description
Enter system
view
system-view
—
Enable DHCP
relay
handshake
dhcp relay
hand enable
Required
Set the interval
at which the
DHCP relay
dynamically
updates the
user address
entries
dhcp-security
tracker
{ interval |
auto }
Optional
Only S3900-EI series switches among S3900
series switches support this configuration
IV. Configuring pseudo-DHCP server detection function
If there is an authorized DHCP server in the network, when a client applies for an IP
address, the authorized DHCP server interconnects with the DHCP client. As a result,
the DHCP client obtains an incorrect IP address. Such unauthorized DHCP server is
called a pseudo DHCP server.

Huawei Quidway S3900 Series Specifications

General

Brand	Huawei
Model	Quidway S3900 Series
Category	Switch
Language	English