Maintaining DHCP
Viewing Statistics About DHCP Messages
Context
Statistics about received and sent DHCP messages provide useful information for fault locating during routine maintenance.
Procedure
- Run the display dhcp server statistics command to check statistics about DHCP messages sent and received on a DHCP server.
- Run the display dhcp relay statistics command to check statistics about DHCP messages sent and received on a DHCP relay agent.
- Run the display dhcp client statistics [ interface interface-type interface-number ] command to check statistics about DHCP messages sent and received on a DHCP client.
- Run the display dhcp statistics command to view statistics about DHCP messages sent and received on a device.
- Run the display dhcp configuration command to check configuration information about the DHCP public module.
Clearing Statistics About DHCP Messages
Context
DHCP statistics cannot be restored after they are cleared. Exercise caution when performing this operation.
Procedure
- Run the reset dhcp server statistics command to clear statistics about DHCP messages sent and received on a DHCP server.
- Run the reset dhcp relay statistics command to clear statistics about DHCP messages sent and received on a DHCP relay agent.
- Run the reset dhcp client statistics [ interface interface-type interface-number ] command to clear statistics about DHCP messages sent and received on a DHCP client.
- Run the reset dhcp statistics command to clear statistics about DHCP messages sent and received on a device.
Resetting a DHCP Address Pool
Context
To force a DHCP server to re-allocate IP addresses to clients or to set IP addresses in an address pool to idle (idle IP addresses will be preferentially allocated), reset an address pool.
Procedure
- Run the following commands to reset address pools on the
device.
Interface address pool:
reset ip pool interface interface-name { start-ip-address [ end-ip-address ] | all | conflict | expired | used }
Global address pool:
reset ip pool name ip-pool-name { start-ip-address [ end-ip-address ] | all | conflict | expired | used }
- Run the reset ip pool import { all | dns | domain-name | nbns } command to clear the DNS and NetBIOS configurations that the address pool automatically obtains and are allocated to the DHCP clients.
- Configure a DHCP relay agent to request a DHCP server to
release IP addresses of clients.
After a DHCP relay agent is configured to request the DHCP server to release IP addresses of clients, it sends DHCP Release messages to the specified DHCP server. After receiving the message, the DHCP server restores specified IP addresses to the idle status. Released IP addresses can then be allocated to other clients. Run the following commands to configure the DHCP relay agent to request the DHCP server to release IP addresses of clients:
- Run the dhcp relay release client-ip-address mac-address [ vpn-instance vpn-instance-name ] [ server-ip-address ] command to request the
DHCP server to release IP addresses allocated to DHCP clients.
The parameter vpn-instance vpn-instance-name cannot be configured in the interface view.
- When you run the preceding command in the system view:
- If no DHCP server is specified, the DHCP relay agent sends DHCP Release messages to all DHCP servers connected to DHCP relay-enabled interfaces.
- If a DHCP server is specified, the DHCP relay agent sends DHCP Release messages to only the specified DHCP server.
- When you run the preceding command in the interface view:
- If no DHCP server is specified, the DHCP relay agent sends DHCP Release messages to the DHCP server connected to this interface.
- If a DHCP server is specified, the DHCP relay agent sends DHCP Release messages to only the specified DHCP server.
- When you run the preceding command in the system view:
- Run the dhcp relay release client-ip-address mac-address [ vpn-instance vpn-instance-name ] [ server-ip-address ] command to request the
DHCP server to release IP addresses allocated to DHCP clients.
Locking a DHCP Address Pool
Context
When a DHCP server is migrated, address pools on the DHCP server need to be transferred to a DHCP server on the live network. To prevent impacting clients that have obtained IP address from the to-be-migrated DHCP server, lock the address pools on the DHCP server. After the migration, new users apply for IP addresses from the new address pool.
Forcing a DHCP Client to Release and Renew Its IP Address
If a DHCP client obtains its IP address dynamically, you can force the client to release and renew its IP address, which is useful during certain troubleshooting procedures.
The commands used to release and renew an IP address depend on the operating system running on the client. For details about the commands to run, see the documentation of your operating system. The commands for some common operating systems are as follows:
Release an IP address.
- For Windows 7, run the ipconfig/release command.
- For MS-DOS of Windows 98, run the winipcfg/release command.
- For Unix-like operating systems, run the dhclient –r command.
Renew an IP address lease or apply for a new IP address.
- For Windows 7, run the ipconfig/renew command.
- For MS-DOS of Windows 98, run the winipcfg/renew command.
- For Unix-like operating systems, run the dhclient command.