Huawei Quidway S3900 Series Operation Manual page 627

Operation Manual - DHCP
Quidway S3900 Series Ethernet Switches-Release 1510
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
Enter
view
Enable
relay
handshake
Set the interval
at which
DHCP
dynamically
updates
user
entries
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.
Command
system
system-view
DHCP
dhcp relay
hand enable
the
dhcp-security
relay
tracker
{ interval
the
auto }
address
Huawei Technologies Proprietary
Chapter 3 DHCP Relay Configuration
Description
—
Required
Optional
Only S3900-EI series switches among S3900
|
series switches support this configuration
3-8