Dynamic Subscriber Interfaces Using DHCP Events Overview

The DHCP event that triggers dynamic creation of subscriber interfaces occurs when either a local DHCP server or external DHCP server assigns an IP address to a subscriber that has issued a DHCP request. After the DHCP server assigns the IP address and the router creates the associated dynamic subscriber interface, the subscriber can access required network services.

DHCP Local Server and Address Allocation

You can configure the DHCP local server to operate in either equal-access mode or standalone mode.

In standalone mode, the DHCP local server provides a basic DHCP service. The server receives a client request for an IP address and immediately allocates the subscriber an IP address from one of the local address pools.

In equal-access mode, the DHCP local server works with Juniper Networks Session and Resource Control (SRC) software and the authorization, accounting, and address assignment utility to provide an advanced subscriber configuration and management service. After the subscriber is authenticated through RADIUS, the DHCP server assigns the subscriber an IP address with a long lease time. This assignment of an IP address triggers the creation of dynamic subscriber interfaces.

For more information about the DHCP servers and the SRC software, see the following chapters:

•  DHCP Overview Information
• SRC-PE Getting Started Guide, Chapter 1, SRC Product Overview

DHCP External Server and Address Allocation

With DHCP external server, all communication between the subscriber and the DHCP server is monitored by the E Series router. The subscriber requests an address from the DHCP server through the E Series router. After the subscriber receives an IP address, the subscriber can access the Internet and use the value-added services provided by the E Series router and by the SRC software. The edge network must be using a DHCP relay function.

The services provided by integrating the E Series router’s DHCP external server application with SRC software are similar to those provided when the DHCP local server is integrated with SRC software. For more information, see SRC-PE Getting Started Guide, Chapter 1, SRC Product Overview.

DHCP Relay Configuration

When you are configuring dynamic subscriber interface support, and you configure DHCP relay in the same virtual router as the dynamic subscriber interfaces, you must use the set dhcp relay inhibit-access-route-creation command to ensure that DHCP replay does not install access internal routes. Otherwise, DHCP relay will overwrite the access internal routes that are originally created for the subscriber interface.

Supported Configurations

E Series routers currently support dynamic creation of subscriber interfaces with DHCP servers in the following configurations:

• IP over Ethernet
• IP over VLAN over Ethernet
• IP over bridged Ethernet over ATM

For example, Figure 1 shows the interface stacking in an IP over Ethernet dynamic subscriber interface configuration. The illustration indicates which layers in the stack are static and dynamic, and identifies the CLI commands typically used to create the configuration.

Figure 1: IP over Ethernet Dynamic Subscriber Interface Configuration

As shown in Figure 1, issuing the ip auto-configure ip-subscriber command configures the primary IP interface to enable dynamic creation of subscriber interfaces. However, the router does not actually create the dynamic subscriber interface until the DHCP server assigns an IP address to the associated subscriber.

To configure each supported configuration, see Example: Configuring Dynamic Subscriber Interfaces .