F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Network Management Configuration Guide-6PW100

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Item Descri
p
tion
Unauthorized Server
Detect
Enable or disable unauthorized DHCP server detection.
There are unauthorized DHCP servers on networks, which reply DHCP clients with
wrong IP addresses.
With this feature enabled, the DHCP relay agent checks whether a request contains
Option 54 (Server Identifier Option). If it does, the DHCP relay agent records in the
option the IP address of the DHCP server that assigned an IP address to the client and
records the receiving interface. The administrator can use this information to check
for unauthorized DHCP servers.
With the unauthorized DHCP server detection enabled, the device records all
detected DHCP servers (including authorized DHCP servers) and saves one record
for each server. The administrator needs to find unauthorized DHCP servers from the
log information.
Dynamic Bindings
Refresh
Enable or disable periodic refresh of dynamic client entries, and set the refresh
interval.
Through 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 and does not remove the
corresponding client entry. To solve this problem, you can enable the periodic
refresh of dynamic client entries.
With this feature, the DHCP relay agent uses the IP address of a client and the MAC
address of the DHCP relay agent 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 specific interval, the DHCP relay agent considers the IP address assignable now
and ages out the client entry. In addition, upon receiving a DHCP-ACK packet, the
DHCP relay agent sends a DHCP-RELEASE to release the IP address.
• If the server returns a DHCP-NAK message, which means the IP address is still in
use, the relay agent does not age it out.
If the Auto option is selected, the refresh interval is calculated by the relay agent
according to the number of client entries.
Track Timer Interval
514BCreating a DHCP server group
1. From the navigation tree, select Network > DHCP > DHCP Relay.
The DHCP relay agent configuration page appears, as shown in
2403HFigure 113.
2. In the Server Group field, click Add.
The page for creating a server group appears.
Figure 114 Creating a server group
3. Configure a DHCP server group as described in 2404HTable 28.
4. Click Apply.