• protocols vstp vlan vlan-id interface• vlans vlan-name interfaceRelatedDocumentationJ-EX Series Switches Interfaces Overview on page 863•• Configuring Gigabit Ethernet Interfaces (CLI Procedure) on page 919• Configuring Aggregated Ethernet Interfaces (CLI Procedure) on page 922• Configuring a Layer 3 Subinterface (CLI Procedure) on page 930• Junos OS Network Interfaces Configuration Guide athttp://www.juniper.net/techpubs/software/junos/• interface-range on page 962Understanding Layer 3 SubinterfacesA Layer 3 subinterface is a logical division of a physical interface that operates at thenetwork level and therefore can receive and forward 802.1Q VLAN tags. You can useLayer 3 subinterfaces to route traffic among multiple VLANs along a single trunk line thatconnects a J-EX Series Switch to a Layer 2 switch. Only one physical connection is requiredbetween the switches. This topology is often called a “router on a stick” or a “one-armedrouter” when the Layer 3 device is a router.To create Layer 3 subinterfaces on a J-EX Series switch, you enable VLAN tagging, partitionthe 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 foreach VLAN. We recommend that you use the VLAN ID as the subinterface number whenyou configure the subinterface. The Junos OS reserves VLAN IDs 0 and 4095.VLAN tagging places the VLAN ID in the frame header, allowing each physical interfaceto handle multiple VLANs. When you configure multiple VLANs on an interface, you mustalso enable tagging on that interface. Junos OS on J-EX Series switches supports a subsetof the 802.1Q standard for receiving and forwarding routed or bridged Ethernet frameswith single VLAN tags and running Virtual Router Redundancy Protocol (VRRP) over802.1Q-tagged interfaces. Double-tagging is not supported.RelatedDocumentationJ-EX Series Switches Interfaces Overview on page 863•• Example: Configuring Layer 3 Subinterfaces for a Distribution Switch and an AccessSwitch on page 893• Junos OS Network Interfaces Configuration Guide athttp://www.juniper.net/techpubs/software/junos/871Chapter 50: Interfaces—Overview
