H3C S5500-EI series Operation Manual page 998

Operation Manual – DHCP
H3C S5500-EI Series Ethernet Switches
Note:
The dhcp relay address-check enable command is independent of other
commands of the DHCP relay agent. That is, the invalid address check takes effect
when this command is executed, regardless of whether other commands are used.
You are recommended to configure IP address check on the interface enabled with
the DHCP relay agent; otherwise, the valid DHCP clients may not be capable of
accessing networks.
When using the dhcp relay security static command to bind a VLAN interface to a
static binding entry, make sure that the VLAN interface is configured as a DHCP
relay agent; otherwise, address entry conflicts may occur.
II. Configuring dynamic binding update interval
Via the DHCP relay agent, a DHCP client sends a DHCP-RELEASE unicast message
to the DHCP server to relinquish its IP address. In this case the DHCP relay agent
simply conveys the message to the DHCP server, thus it does not remove the IP
address from its bindings. To solve this, the DHCP relay agent can update dynamic
bindings at a specified interval.
The DHCP relay agent uses the IP address of a client and the MAC address of the
DHCP relay interface to regularly send a DHCP-REQUEST message to the DHCP
server.
If the server returns a DHCP-ACK message or does not return any message within
a specified interval, which means the IP address is assignable now, the DHCP
relay agent will update its bindings by aging out the binding entry of the IP
address.
If the server returns a DHCP-NAK message, which means the IP address is still in
use, the relay agent will not age it out.
Follow these steps to configure dynamic binding update interval:
To do...
Enter system view
Configure binding
update interval
Chapter 3 DHCP Relay Agent Configuration
Use the command...
system-view
dhcp relay security
tracker { interval | auto }
3-7
Remarks
—
Optional
auto by default. (auto interval is
calculated by the relay agent
according to the number of
bindings.)