# Configuring the DHCP External Server to Support the Creation of Dynamic Subscriber Interfaces

You can configure the DHCP external server to support the creation of dynamic subscriber interfaces. This configuration requires that the user’s DHCP control traffic and data traffic traverse the same client-facing ingress port on the E Series router.

You must use the ip dhcp-external auto-configure command within a specific virtual router context.

To configure the DHCP external server to support the creation of dynamic subscriber interfaces:

- Issue the ip dhcp-external auto-configure command from Global Configuration mode:
  host1(config)#ip dhcp-external auto-configure

To configure the DHCP external server to support the creation of dynamic subscriber interfaces built over dynamic VLANs that are based on the agent-circuit-id option (suboption 1) of the option 82 field in DHCP messages, include the agent-circuit-identifier keyword.

- Issue the ip dhcp-external auto-configure command with the agent-circuit-identifier keyword from Global Configuration mode:
  host1(config)#ip dhcp-external auto-configure agent-circuit-identifier

  The use of the option 82 field enables you to stack an IP interface that is associated with a particular subscriber over a dynamically created VLAN; the VLAN is dynamically created based on the agent-circuit-id option (suboption 1) that is contained in the DHCP option 82 field.

  For information about configuring agent-circuit-id–based dynamic VLAN subinterfaces, see the Configuring Dynamic Interfaces Using Bulk Configuration chapter in JunosE Link Layer Configuration Guide.

#### Related Topics

- ip dhcp-external auto-configure