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# Overview

Before you begin configuring dynamic interfaces, review the concepts described in this section.

A dynamic interface is created automatically and transparently through some external event, typically through the receipt of data over a lower-layer link, such as an ATM virtual circuit (VC) or a virtual LAN (VLAN).

The layers of a dynamic interface are created based on the packets received on the link and can be configured through any one of the following:

- RADIUS authentication
- Profiles
- A combination of RADIUS authentication and profiles

You create and configure each layer of a static interface manually through an existing configuration mechanism such as the command-line interface (CLI) or Simple Network Management Protocol (SNMP).

Unlike static interfaces, dynamic interfaces are not restored through nonvolatile storage (NVS) after a reboot.

## Types of Dynamic Interfaces

There are two types of dynamic interfaces: upper-layer and bulk-configured. This chapter describes upper-layer dynamic interfaces, which enable you to dynamically create the following configurations:

- Dynamic IP, PPPoE, PPP, MLPPP, and bridged Ethernet interfaces over a static ATM 1483 interface
- Dynamic PPPoE subinterfaces over a static PPPoE major interface

Bulk-configured dynamic interfaces enable you to dynamically create ATM 1483 subinterfaces and VLAN subinterfaces by bulk-configuring a range of identifiers. For more information, see Configuring Dynamic Interfaces Using Bulk Configuration.

## Autodetection

The router performs autodetection, also referred to as autosensing, to determine the layers of each dynamic interface. The autodetection process occurs when the router conditionally constructs interface layers based on the encapsulation type of the incoming packet.

Autodetection only uses system resources on demand based on what is detected in the incoming packet. Dynamic interfaces are created as a result of traffic on the interface. Dynamic interfaces can also be dynamically deleted without your intervention, thereby enabling any consumed system resources to be returned.

Unlike dynamic interfaces, static interfaces always allocate system resources upon creation, and always consume system resources, even when the interface is quiescent.

## Upper-Layer Dynamic Interface Configurations

E-series routers support the following types of upper-layer dynamic interface configurations:

- Dynamic IP over static ATM 1483 (IPoA)
- Dynamic IP over dynamic PPP over static ATM 1483
- Dynamic IP over dynamic PPP over dynamic PPPoE over static ATM 1483
- Dynamic IP over dynamic bridged Ethernet over static ATM 1483
- Dynamic IP over dynamic MLPPP over static ATM 1483
- Dynamic IP over dynamic MLPPP over dynamic PPPoE over static ATM 1483
- Dynamic IP over dynamic PPP over dynamic PPPoE subinterface over static PPPoE major interface (with or without VLANs)
- Dynamic IP over dynamic MLPPP over dynamic PPPoE subinterface over static PPPoE major interface (with or without VLANs)
- Dynamic IP over dynamic MLPPP over dynamic PPPoE (with or without VLANs)

Internet Protocol version 4 (IPv4) is supported for all of these upper-layer dynamic interface configurations.

Currently, Internet Protocol version 6 (IPv6) is supported only when PPP or MLPPP is the layer immediately below the IPv6 layer in the interface column. Dynamic IPv6 is not supported directly over static ATM 1483, dynamic bridged Ethernet, or dynamic VLANs. Upper-layer dynamic interface columns that support IPv6 include the following:

- Dynamic IPv6 over dynamic PPP over static ATM 1483
- Dynamic IPv6 over dynamic MLPPP over static ATM 1483
- Dynamic IPv6 over dynamic PPP over dynamic PPPoE over static ATM 1483
- Dynamic IPv6 over dynamic MLPPP over dynamic PPPoE over static ATM 1483
- Dynamic IPv6 over dynamic PPP over dynamic PPPoE subinterface over static PPPoE major interface (with or without VLANs)
- Dynamic IPv6 over dynamic MLPPP over dynamic PPPoE subinterface over static PPPoE major interface (with or without VLANs)

For more information about IPv4, see chapter Configuring IP in JUNOSe IP, IPv6, and IGP Configuration Guide. For more information about IPv6, see chapter Configuring IPv6 in JUNOSe IP, IPv6, and IGP Configuration Guide.

## Profiles

You can use profiles to configure dynamic interfaces. A profile is a set of characteristics that can be dynamically assigned to interfaces. By using a profile, you reduce the management of a large number of interfaces by applying a set of characteristics to multiple interfaces.

When you are configuring a large number of interfaces with the same attributes at the higher layers, you can use a profile to factor out all the common attributes of each layer into one place. This action affects one or more dynamic layers of the interface column. After you define the static lower layers, you assign a profile to the highest static layer of the interface column.

When a dynamic interface is configured, the configuration data received from the RADIUS authentication server typically overrides configuration data obtained from a profile.

In contrast to static PPP interfaces (above which only dynamic IP interfaces can be created), static ATM 1483 subinterfaces support recognition and creation of the following upper dynamic interface types or encapsulations:

- Bridged Ethernet
- IP
- IPv6
- Multilink PPP
- PPP
- PPPoE

The auto-configure command identifies the encapsulation type. For flexibility, the router provides the ability to configure an ATM 1483 subinterface with distinct profile assignments for each encapsulation type supported by the auto-configure command. For more information about using this command, see auto-configure Command.

## RADIUS Authentication

RADIUS helps protect your network against unauthorized access. To accomplish this, RADIUS clients running on your router send authentication requests to a central RADIUS server. You can configure dynamic interfaces over interfaces through RADIUS authentication.

When a packet is received, the authenticating interface, either PPP or ATM 1483, establishes a session with RADIUS and passes the username and password to the RADIUS server. For dynamic IPoA or dynamic bridged Ethernet, the RADIUS username and password are obtained from the information specified by the subscriber command. The RADIUS server returns a grant or deny indication. If authentication is granted, the RADIUS attributes are returned, a user login is created, and the dynamic interfaces are configured from the RADIUS attributes.

ATM 1483 interfaces may receive configuration data from the RADIUS server in the form of traffic-shaping parameters.

Any changes made to a RADIUS configuration for a given dynamic interface do not take effect until an existing dynamic interface configured from this RADIUS entry is re-created, that is, deleted and then dynamically created.

## ATM Oversubscription for Dynamic Interfaces

You can take advantage of oversubscription of static ATM 1483 subinterfaces and bulk-configured ATM VCs with the following dynamic interface configurations:

- The router supports oversubscription of static ATM 1483 subinterfaces when you configure the static ATM 1483 subinterface to support one of the following dynamic upper-layer encapsulation types: bridged Ethernet, IP, Multilink PPP, PPP, and PPPoE interfaces. For information about configuring dynamic upper-layer encapsulation types over a static ATM 1483 subinterface, see About Configuring Dynamic Interfaces over Static ATM.
- The router supports oversubscription of bulk-configured VC ranges when you create a bulk-configured VC range on a static ATM AAL5 interface for use by a dynamic ATM 1483 subinterface. For information about configuring dynamic ATM 1483 subinterfaces with bulk-configured VC ranges, see Configuring ATM 1483 Dynamic Subinterfaces in Configuring Dynamic Interfaces Using Bulk Configuration.

### How Oversubscription Works

Oversubscription is based on the capabilities of the ATM line module on which the dynamic interface is configured. For details about the capabilities of specific ATM line modules, see either Module Capabilities in Configuring ATM , or the Link Layer Maximums tables in JUNOSe Release Notes, Appendix A, System Maximums.

Each ATM line module supports a maximum number of configured subinterfaces or VCs, and a smaller maximum number of subinterfaces or VCs that can be active at any one time. The maximum number of active subinterfaces or VCs determines the number of subscribers that can connect to the router through this line module at any one time.

As a result, you can oversubscribe static ATM 1483 subinterfaces or bulk-configured VC ranges by creating up to the maximum number of configured subinterfaces or VCs supported on the module, knowing that no more than the maximum number of active subinterfaces or VCs can be connected to the router at any one time.

### Static ATM 1483 Subinterfaces

An active static ATM 1483 subinterface currently supports a dynamic upper-layer encapsulation type such as PPP or PPPoE. For ATM line modules that support ATM subinterface oversubscription, the maximum number of active subinterfaces supported per module is less than the maximum number of configured subinterfaces supported per module.

When the maximum number of active ATM 1483 subinterfaces has been reached, the router prevents all additional subscribers from connecting to the line module until at least one currently active subscriber logs out, which causes the router to tear down the dynamic interface column for that subscriber. When a dynamic interface column is torn down, the router enables the first currently inactive subscriber that receives traffic to connect to the router and become active as a replacement for the subscriber that logged out.

#### Example

Consider an ATM line module that supports a maximum of 16,000 configured subinterfaces and a maximum of 8000 active subinterfaces. If all 16,000 static ATM 1483 subinterfaces attempt to connect to the router, only the first 8000 subinterfaces to receive traffic are able to log in, generate dynamic interface columns, and become active. When a subscriber connected through one of these active subinterfaces logs out, the router enables the first of the remaining 8000 inactive subinterfaces that receives traffic to connect as a replacement for the subscriber that logged out.

### Bulk-Configured VC Ranges

An active bulk-configured VC range is associated with a dynamic ATM 1483 subinterface that supports a dynamic upper-layer encapsulation type. For ATM line modules that support VC oversubscription, the maximum number of active bulk-configured VCs per line module is less than the maximum number of individual VCs created from the total number of bulk-configured VC ranges that the line module supports.

For details about how oversubscription works for bulk-configured VC ranges, see ATM Oversubscription for Bulk-Configured VC Ranges in Configuring Dynamic Interfaces Using Bulk Configuration.

### Combination of Static ATM 1483 Subinterfaces and Bulk-Configured VC Ranges

ATM line modules are sometimes configured with a combination of static ATM 1483 subinterfaces and bulk-configured VC ranges. In these configurations, both the static ATM 1483 subinterfaces and bulk-configured VC ranges can support active subinterfaces. The combined total of active static ATM 1483 subinterfaces, and active dynamic ATM 1483 subinterfaces created from bulk-configured VC ranges, cannot exceed the maximum number of active subinterfaces supported by the line module.

For details about how oversubscription works for ATM modules configured with both static ATM 1483 subinterfaces and bulk-configured VC ranges, see ATM Oversubscription for Bulk-Configured VC Ranges in Configuring Dynamic Interfaces Using Bulk Configuration.

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