HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Services Conf - Page 48

Enabling offline detection, Configuring the DHCP relay agent to release an IP address

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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, it discards the DHCP request. To enable MAC address check: Step 1. Enter system view. 2. Enter interface view. 3. Enable MAC address check. Command system-view interface interface-type interface-number dhcp relay check mac-address Remarks N/A N/A Disabled by default 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. 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. To enable offline detection: Step 1. Enter system view. 2. Enter interface view. 3. Enable offline detection. Command system-view interface interface-type interface-number dhcp relay client-detect enable Remarks N/A N/A Disabled by default Configuring the DHCP relay agent to release an IP address You can configure the relay agent to release a client's IP address. The relay agent sends a DHCP-RELEASE message that contains the IP address. Upon receiving the DHCP-RELEASE message, the DHCP server releases the IP address. Meanwhile, the client entry is removed from the DHCP relay agent. Dynamic client entries can be generated after you enable address check or IP source guard on the DHCP relay agent. For more information about IP source guard, see Security Configuration Guide. To configure the DHCP relay agent to send DHCP-RELEASE messages: 40

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40
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, it discards the DHCP request.
To enable MAC address check:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter interface view.
interface
interface-type
interface-number
N/A
3.
Enable MAC address
check.
dhcp relay check mac-address
Disabled by default
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. 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.
To enable offline detection:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter interface view.
interface
interface-type
interface-number
N/A
3.
Enable offline detection.
dhcp relay client-detect enable
Disabled by default
Configuring the DHCP relay agent to release an IP
address
You can configure the relay agent to release a client's IP address. The relay agent sends a
DHCP-RELEASE message that contains the IP address. Upon receiving the DHCP-RELEASE message, the
DHCP server releases the IP address. Meanwhile, the client entry is removed from the DHCP relay agent.
Dynamic client entries can be generated after you enable address check or IP source guard on the DHCP
relay agent. For more information about IP source guard, see
Security Configuration Guide
.
To configure the DHCP relay agent to send DHCP-RELEASE messages: