S-Vlan Overview; Figure 13: Use Of Vlans To Multiplex Different Protocols Over A Single Physical - Juniper JUNOSE SOFTWARE 11.0.X - LINK LAYER CONFIGURATION GUIDE 4-1-2010 Configuration Manual

JUNOSe 11.0.x Link Layer Configuration Guide
identifier (VCI) to multiplex the different channels over the physical link. The Ethernet
protocol type serves the same function within a VLAN as the logical link control (LLC)
subnetwork attachment point (SNAP) within a VC, to multiplex the different protocols
over the channel.
Figure 13: Use of VLANs to Multiplex Different Protocols over a Single Physical Link
ERX14xx models (rear view)
In a VLAN configuration, the router can send VLAN 0 tagged or untagged frames.
All VLAN subinterfaces use the MAC address of the Ethernet interface over which
they are configured. However, some configurations, such as multiple IP over VLAN
subinterfaces, require that you connect many VLAN subinterfaces to a single device.
In these cases, the device uses the MAC address to identify and select the correct
VLAN to use. When the MAC address is the same for all VLANs, uneven load balancing
of traffic occurs. To ensure proper load balancing, you must assign unique MAC
addresses to the individual VLAN subinterfaces that are connected to the device. Any
ARP requests and responses generated for the IP address assigned to a VLAN
subinterface use this MAC address.
You must assign the MAC address when you configure the VLAN ID. If you change
the MAC address of the VLAN subinterface after you configure it, system errors can
occur. To change the MAC address, you must first remove the VLAN subinterface
and then reconfigure it.
For more information, see:

S-VLAN Overview

As described in "VLAN Overview" on page 169, VLANs permit multiplexing multiple
IP interfaces and PPPoE interfaces over a single physical Ethernet port by creating
VLAN subinterfaces. As specified in IEEE Standard 802.1q, the 12-bit VLAN identifier's
tagged frames enables the construction of a maximum of 4096 distinct VLANs. In
an Ethernet B-RAS application environment, however, this VLAN limit is inadequate.
170
S-VLAN Overview
Chapter Configuring IP in JUNOSe IP, IPv6, and IGP Configuration Guide
"Configuring Point-to-Point Protocol over Ethernet" on page 325