R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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NOTE:
• The dhcp relay address-check enable command can be executed only on Layer 3 Ethernet interfaces
(including sub-interfaces).
• Before enabling address check on an interface, you must enable the DHCP service, and enable the
DHCP relay agent on the interface; otherwise, the address check configuration is ineffective.
• The dhcp relay address-check enable command only checks IP and MAC addresses but not interfaces.
• When using the dhcp relay security static command to bind an interface to a static binding entry, make
sure that the interface is configured as a DHCP relay agent; otherwise, address entry conflicts may
occur.
• When a synchronous/asynchronous serial interface requests an IP address through DHCP, the DHCP
relay agent does not record the corresponding IP-to-MAC binding.
2. Configuring periodic refresh of dynamic client entries
A DHCP client unicasts a DHCP-RELEASE message to the DHCP server when releasing its dynamically
obtained IP address. The DHCP relay agent simply conveys the message to the DHCP server and does
not remove the IP-to-MAC binding. To solve this problem, the periodic refresh of dynamic client entries
feature is introduced.
With this feature, the DHCP relay agent uses the IP address of a client and the MAC address of the DHCP
relay interface to periodically 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, the DHCP relay agent ages out the client entry.
• If the server returns a DHCP-NAK message, the relay agent keeps the client entry.
To configure periodic refresh of dynamic client entries:
Ste
p
Command Remarks
1. Enter system view.
system-view N/A
2. Enable periodic refresh
of dynamic client entries.
dhcp relay security refresh
enable
Optional.
Enabled by default.
3. Configure the refresh
interval.
dhcp relay security tracker
{ interval | auto }
Optional.
auto by default. (auto interval is calculated
by the relay agent according to the number
of client entries.)
3. Enabling unauthorized DHCP server detection
Unauthorized DHCP servers may assign wrong IP addresses to DHCP clients.
With unauthorized DHCP servers detection enabled, the DHCP relay agent checks whether a request
contains Option 54 (Server Identifier Option). If yes, the DHCP relay agent records the IP address in the
option, which is the IP address of the DHCP server that assigned an IP address to the DHCP client, and
records the receiving interface. The administrator can use this information to check for unauthorized
DHCP servers.
To enable unauthorized DHCP server detection: