Understanding Layer 3 Subinterfaces - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Complete Software Guide for Junos

Understanding Layer 3 Subinterfaces

Related
Documentation
1248
®
OS for EX Series Ethernet Switches, Release 10.4
See the Junos OS Network Interfaces Configuration Guide.
interface-range on page 1391
A Layer 3 subinterface is a logical division of a physical interface that operates at the
network level and therefore can receive and forward 802.1Q VLAN tags. You can use
Layer 3 subinterfaces to route traffic among multiple VLANs along a single trunk line that
connects a Juniper Networks EX Series Ethernet Switch to a Layer 2 switch. Only one
physical connection is required between the switches. This topology is often called a
"router on a stick" or a "one-armed router" when the Layer 3 device is a router.
To create Layer 3 subinterfaces on an EX Series switch, you enable VLAN tagging, partition
the physical interface into logical partitions, and bind the VLAN ID to the logical interface.
You can partition one physical interface into up to 4094 different subinterfaces, one for
each VLAN. We recommend that you use the VLAN ID as the subinterface number when
you configure the subinterface. Juniper Networks Junos operating system (Junos OS)
reserves VLAN IDs 0 and 4095.
VLAN tagging places the VLAN ID in the frame header, allowing each physical interface
to handle multiple VLANs. When you configure multiple VLANs on an interface, you must
also enable tagging on that interface. Junos OS on EX Series switches supports a subset
of the 802.1Q standard for receiving and forwarding routed or bridged Ethernet frames
with single VLAN tags and running Virtual Router Redundancy Protocol (VRRP) over
802.1Q-tagged interfaces. Double-tagging is not supported.
EX Series Switches Interfaces Overview on page 1239
Example: Configuring Layer 3 Subinterfaces for a Distribution Switch and an Access
Switch on page 1267
See the Junos OS Network Interfaces Configuration Guide.
Copyright © 2010, Juniper Networks, Inc.