# Configuring DHCP External Server to Control Preservation of Dynamic Subscriber Interfaces

You can configure the DHCP external server application to delete and re-create the dynamic subscriber interface after a bound client restarts the discovery process on the its primary IP interface. By default, the DHCP external server preserves the existing dynamic subscriber interface in this situation.

Deleting and re-creating the dynamic subscriber interface for a DHCP client may trigger additional authentication, authorization, and accounting (AAA) services if AAA is configured on the router. Therefore, issuing the ip dhcp-external recreate-subscriber-interface command to delete and re-create the dynamic subscriber interface is useful if you want to use AAA services to validate and collect subscriber information during a restart of the DHCP discovery process.

Preserving the client’s dynamic subscriber interface is useful if deleting and re-creating the dynamic subscriber interface might result in a service interruption.

To enable the DHCP external server application to delete and re-create the dynamic subscriber interface after a bound client restarts the discovery process on its primary IP interface:

- Issue the ip dhcp-external recreate-subscriber-interface command from Global Configuration mode:

host1:vr1(config)#ip dhcp-external recreate-subscriber-interface

To restore the DHCP external server default behavior to preserve the dynamic subscriber interface after a bound client restarts the discovery process on its primary IP interface:

- Issue the no ip dhcp-external recreate-subscriber-interface command from Global Configuration mode:

host1:vr1(config)#no ip dhcp-external recreate-subscriber-interface

| Note: If you are upgrading the JunosE Software on the router from a release in which the DHCP external server deleted and re-created the dynamic subscriber interface by default, you must explicitly issue the ip dhcp-external recreate-subscriber-interface command in the current release to delete and re-create the dynamic subscriber interface. The router no longer deletes and re-creates the dynamic subscriber interface by default in this situation. For a list of the JunosE releases in which deleting and re-creating the dynamic subscriber interface was the default behavior for the DHCP external server, see DHCP External Server in the Known Behavior section of the JunosE Release Notes.

#### Related Documentation

- Preservation of Dynamic Subscriber Interfaces with DHCP External Server Overview
- ip dhcp-external recreate-subscriber-interface