Enabling Offline Detection; Configuring The Dhcp Relay Agent To Release An Ip Address - HP A5120 EI Series Configuration Manual

address field of the frame. If they are the same, the DHCP relay agent decides this request as valid
and forwards it to the DHCP server; if not, the DHCP request is discarded.
Follow these steps to enable MAC address check:
To do...
Enter system view
Enter interface view
Enable MAC address check
NOTE:
DHCP relay agents change the source MAC addresses when forwarding DHCP packets. Therefore, you
can enable MAC address check only on a DHCP relay agent directly connected to DHCP clients.
Otherwise, valid DHCP packets may be discarded and clients cannot obtain IP addresses.

Enabling offline detection

The DHCP relay agent checks whether a user is online by learning the ARP entry. When an ARP entry is
aged out, the corresponding client is considered to be offline.
With this function enabled on an interface, the DHCP relay agent removes a client's IP-to-MAC entry
when it is aged out, and sends a DHCP-RELEASE message to the DHCP server to release the IP address of
the client.
Follow these steps to enable offline detection:
To do...
Enter system view
Enter interface view
Enable offline detection
NOTE:
Removing an ARP entry manually does not remove the corresponding client's IP-to-MAC binding.
When the client goes offline, use the undo dhcp relay security command to remove the IP-to-MAC
binding manually.
Configuring the DHCP relay agent to release an IP
address
After you configure the DHCP relay agent to release a client's IP address, the DHCP relay agent sends a
DHCP-RELEASE message that contains the specified IP address to the server. Upon receiving the DHCP-
RELEASE message, the DHCP server releases the IP address. The DHCP relay agent removes the client
entry.
Use the command...
system-view
interface interface-type interface-
number
dhcp relay check mac-address
Use the command...
system-view
interface interface-type interface-
number
dhcp relay client-detect enable
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Remarks
—
—
Required
Disabled by default.
Remarks
—
—
Required
Disabled by default.