# Overview

Bridged Ethernet allows multiple upper-layer interface types (IP and PPPoE) to be simultaneously multiplexed over the same interface. You can set up the router to either terminate interfaces and route data or to pass data transparently through the router to another terminating device. This capability supports multiple client devices that use both IP and Point-to-Point Protocol over Ethernet (PPPoE) encapsulation over an Ethernet LAN.

| Note: Although connection-based forwarding is not supported on any E Series router, as an alternative, you can configure a local cross-connect, which uses layer 2 services over MPLS to transmit data between two layer 2 interfaces that reside on the same E Series router. Configuration of local cross-connects is supported on all E Series routers. For more information about configuring local cross-connects, see Configuring Layer 2 Services over MPLS in JunosE BGP and MPLS Configuration Guide.

## Bridged Ethernet Application

Figure 43 shows an example of a client computer using IP/PPP/PPPoE and an Internet gaming system running IP, connecting to the E Series router over the same ATM PVC. The client computer and gaming system can connect to an E Series router via an xDSL modem over a single ATM PVC, and the router can forward these two data streams independently. When the router receives the two data streams, it uses the Ethertype contained in the bridged Ethernet header to select which upper interface (IP or PPPoE) receives the frame.

In Figure 43, IP and PPPoE interfaces are configured so that the non-PPPoE IP traffic is received by the IP interface, and the IP/PPP/PPPoE traffic is received by the PPPoE interface. Since the router receives these data streams on different IP interfaces, they may be routed independently.

Figure 43: Bridged Ethernet Topology, Router Terminating and Routing Traffic

## Assigning MAC Addresses

When you create a bridged Ethernet interface, the system media access control (MAC) address is assigned to the interface by default. However, you can assign a specific MAC address to each statically configured bridged Ethernet interface. For example, if multiple statically configured bridged Ethernet interfaces are connected to the same device, using specific MAC addresses enables the connected device to select the correct ATM port or VC to use.

You configure a specific MAC address when you create the bridged Ethernet interface. If you want to modify an existing MAC address, you must remove the interface and create it again. Also, you cannot configure multicast MAC addresses on bridged Ethernet interfaces.

## VLAN and S-VLAN Configurations

Bridged Ethernet interfaces on E Series routers support the configuration of virtual local area networks (VLANs) and stacked virtual local area networks (S-VLANs). A VLAN permits multiplexing multiple higher-level protocols over a single physical port. An S-VLAN provides a two-level VLAN tag structure, which extends the VLAN ID space to more than 16 million VLAN tags.

Specifically, you can statically configure the following higher-level protocols over a VLAN or an S-VLAN subinterface that is stacked above a bridged Ethernet interface:

- IP
- MPLS
- PPPoE
- Transparent bridging

Figure 44 illustrates the interface stacking supported on E Series routers for VLANs over bridged Ethernet.

Figure 44: Interface Stacking for VLANs over Bridged Ethernet

VLANs and S-VLANs configured over bridged Ethernet interfaces provide the same basic capabilities as VLANs and S-VLANs configured over Ethernet interfaces, with the following exception:

- S-VLAN oversubscription is not supported on bridged Ethernet interfaces.

After you configure the bridged Ethernet interface, you configure the VLANs, S-VLANs, and the supported higher-level protocols in the same way that you configure them over Ethernet interfaces.

For more information, see:

- Configuring VLAN and S-VLAN Subinterfaces for introductory information about VLANs and S-VLANs.
- Configuring VLANs over Bridged Ethernet and Configuring S-VLANs over Bridged Ethernet for examples that illustrate VLAN and S-VLAN configurations over bridged Ethernet.