Tagging

Junos VLAN Tagging Options Explained

Here’s a comparison of vlan-tagging, flexible-vlan-tagging, and encapsulation flexible-ethernet-services.

1. vlan-tagging

• Configuration Level: Physical Interface (set interfaces <interface-name> vlan-tagging)
• Purpose: Enables basic IEEE 802.1Q VLAN tagging support on the physical interface.
• Capabilities:
  • Allows logical units (unit) under this interface to be configured with a single VLAN ID (set interfaces <interface-name> unit <number> vlan-id <id>).
  • Supports sending and receiving standard single-tagged Ethernet frames.
  • Can support one untagged VLAN using the native-vlan-id option on the physical interface.
• Limitations:
  • Does not natively support receiving or sending double-tagged (QinQ/Stacked VLAN) frames on logical units.
  • Does not easily support mixing tagged and untagged traffic across different logical units on the same physical interface (only one native/untagged VLAN is easily supported for the whole port).
  • Limited flexibility in VLAN mapping per logical unit.
• Typical Use Case:
  • Standard “trunk” ports connecting to switches or other routers where multiple VLANs, each identified by a single tag, need to be carried.
  • Simple Layer 2 or Layer 3 sub-interfaces.
• Example:

  # Configure the physical interface for basic single-tagging
  set interfaces ge-0/0/1 vlan-tagging
  set interfaces ge-0/0/1 native-vlan-id 10  # Optional: VLAN 10 is untagged
  
  # Configure logical units with single VLAN IDs
  set interfaces ge-0/0/1 unit 100 vlan-id 100
  set interfaces ge-0/0/1 unit 100 family inet address 192.168.100.1/24
  
  set interfaces ge-0/0/1 unit 200 vlan-id 200
  set interfaces ge-0/0/1 unit 200 family inet address 192.168.200.1/24
  

2. flexible-vlan-tagging

• Configuration Level: Physical Interface (set interfaces <interface-name> flexible-vlan-tagging)
• Purpose: Enables advanced VLAN tagging capabilities, allowing for more complex scenarios on a single physical interface.
• Capabilities:
  • Supports logical units with single VLAN IDs (vlan-id).
  • Supports logical units with double (stacked/QinQ) VLAN tags (vlan-tags outer <tag> inner <tag>).
  • Supports logical units accepting untagged traffic (vlan-id none, though configuration details vary slightly by platform/scenario).
  • Allows mixing single-tagged, double-tagged, and untagged logical units on the same physical interface.
  • Supports VLAN ID lists and ranges on logical units (vlan-id-list [ list-of-vlans ]).
  • Often a prerequisite for advanced Layer 2 features and services.
• Limitations:
  • Slightly more complex configuration as each logical unit’s tagging requirement must be explicitly defined.
• Typical Use Case:
  • QinQ deployments (Service Provider NNI, Enterprise Campus).
  • Interfaces needing to handle a mix of single-tagged customer traffic and double-tagged infrastructure traffic.
  • Interfaces where some services are tagged and others are untagged.
  • Aggregation points requiring flexible VLAN mapping.
• Example:

  # Configure the physical interface for advanced tagging
  set interfaces xe-0/1/0 flexible-vlan-tagging
  
  # Configure a logical unit for single-tagged traffic
  set interfaces xe-0/1/0 unit 101 description "Single Tagged Customer A"
  set interfaces xe-0/1/0 unit 101 vlan-id 101
  set interfaces xe-0/1/0 unit 101 family bridge # Example for L2
  
  # Configure a logical unit for double-tagged (QinQ) traffic
  set interfaces xe-0/1/0 unit 500 description "QinQ Customer B (Outer 500, Inner 50)"
  set interfaces xe-0/1/0 unit 500 vlan-tags outer 500 inner 50
  set interfaces xe-0/1/0 unit 500 family bridge # Example for L2
  
  # Configure a logical unit for untagged traffic (config might vary slightly)
  # This often requires specific encapsulation like vlan-bridge or ethenet-bridge
  set interfaces xe-0/1/0 unit 0 description "Untagged Management"
  set interfaces xe-0/1/0 unit 0 encapsulation vlan-bridge
  # Note: No 'vlan-id' or 'vlan-tags' means it might handle untagged frames if configured correctly
  set interfaces xe-0/1/0 unit 0 family inet address 10.0.0.1/24
  
  # Configure a logical unit accepting a list of VLANs
  set interfaces xe-0/1/0 unit 999 description "VLAN List Service"
  set interfaces xe-0/1/0 unit 999 vlan-id-list [ 200 205-210 300 ]
  set interfaces xe-0/1/0 unit 999 encapsulation vlan-bridge
  

3. encapsulation flexible-ethernet-services

• Configuration Level: Physical Interface (set interfaces <interface-name> encapsulation flexible-ethernet-services)
• Purpose: Primarily used on MX Series routers (and some other platforms) to allow a mix of different Layer 2 encapsulation types (like bridge, ccc, vpls) on different logical units of the same physical interface. It fundamentally changes how the interface PFE (Packet Forwarding Engine) processes frames to support this service flexibility.
• Capabilities:
  • Allows logical units (unit) under the same physical interface to have different Ethernet service encapsulations (e.g., encapsulation vlan-bridge, encapsulation vlan-ccc, encapsulation vlan-vpls, encapsulation ethernet-ccc, etc.).
  • Enables maximum service multiplexing onto a single physical port.
• Important Note: This option must often be used in conjunction with flexible-vlan-tagging if the services running on the logical units need to handle tagged frames (single or double). flexible-ethernet-services defines the service type flexibility, while flexible-vlan-tagging defines the VLAN tag flexibility.
• Limitations:
  • Platform-specific (mainly MX Series).
  • Adds configuration complexity.
  • Cannot be combined with vlan-tagging on the same physical interface.
• Typical Use Case:
  • Service Provider edge routers (PE) terminating multiple customers with different L2VPN service types (E-Line/CCC, E-LAN/VPLS, E-Tree) or bridging requirements on the same physical link (NNI or UNI).
  • Data Center interconnects requiring diverse L2 service types.
• Example:

  # Configure the physical interface for flexible service encapsulations AND flexible tagging
  set interfaces xe-0/2/0 encapsulation flexible-ethernet-services
  set interfaces xe-0/2/0 flexible-vlan-tagging
  
  # Logical unit for a bridged service (single tag)
  set interfaces xe-0/2/0 unit 1000 description "Bridged Service VLAN 1000"
  set interfaces xe-0/2/0 unit 1000 encapsulation vlan-bridge
  set interfaces xe-0/2/0 unit 1000 vlan-id 1000
  
  # Logical unit for a VPLS service (QinQ tag)
  set interfaces xe-0/2/0 unit 2000 description "VPLS Service Outer 200 Inner 20"
  set interfaces xe-0/2/0 unit 2000 encapsulation vlan-vpls
  set interfaces xe-0/2/0 unit 2000 vlan-tags outer 200 inner 20
  
  # Logical unit for a CCC/L2Circuit service (single tag)
  set interfaces xe-0/2/0 unit 3000 description "CCC/E-Line Service VLAN 3000"
  set interfaces xe-0/2/0 unit 3000 encapsulation vlan-ccc
  set interfaces xe-0/2/0 unit 3000 vlan-id 3000
  

Summary Table

In essence:

• Use vlan-tagging for the simplest trunk port needs.
• Use flexible-vlan-tagging when you need any advanced VLAN tagging like QinQ or mixing tagged/untagged traffic on different units of the same port.
• Use encapsulation flexible-ethernet-services (usually with flexible-vlan-tagging) on platforms like MX when you need to run different types of Layer 2 services (bridging, VPLS, CCC, etc.) concurrently on logical units sharing the same physical interface.