Encapsulation Capabilities

When you configure a point-to-point encapsulation (such as PPP or Cisco HDLC) on a physical interface, the physical interface can have only one logical interface (that is, only one unit statement) associated with it. When you configure a multipoint encapsulation (such as Frame Relay), the physical interface can have multiple logical units, and the units can be either point-to-point or multipoint.

Ethernet CCC encapsulation for Ethernet interfaces with standard TPID tagging requires that the physical interface have only a single logical interface. Ethernet interfaces in VLAN mode can have multiple logical interfaces.

For Ethernet interfaces in VLAN mode, VLAN IDs are applicable as follows:

• VLAN ID 0 is reserved for tagging the priority of frames.
• For encapsulation type vlan-ccc, VLAN IDs from 1 through 511 are reserved for normal VLANs, and VLAN IDs 512 and above are reserved for CCC VLANs.
• For encapsulation type vlan-vpls, VLAN IDs 1 through 511 are reserved for normal VLANs, and VLAN IDs 512 and above are reserved for VPLS VLANs.
• For encapsulation types extended-vlan-ccc and extended-vlan-vpls, all VLAN IDs are valid.

The upper limits for configurable VLAN IDs vary by interface type. For more information, see Configure 802.1Q VLANs and Table 22.

When you configure a TCC encapsulation, some modifications are needed to handle VPN connections over unlike Layer 2 and Layer 2.5 links and terminate the Layer 2 and Layer 2.5 protocol locally. The router performs the following media-specific changes:

• PPP TCC—Both Link Control Protocol (LCP) and Network Control Protocol (NCP) are terminated on the router. Internet Protocol Control Protocol (IPCP) IP address negotiation is not supported. The JUNOS software strips all PPP encapsulation data from incoming frames before forwarding them. For output, the next hop is changed to PPP encapsulation.
• Cisco HDLC TCC—Keepalive processing is terminated on the router. The JUNOS software strips all Cisco HDLC encapsulation data from incoming frames before forwarding them. For output, the next hop is changed to Cisco HDLC encapsulation.
• Frame Relay TCC—All Local Management Interface (LMI) processing is terminated on the router. The JUNOS software strips all Frame Relay encapsulation data from incoming frames before forwarding them. For output, the next hop is changed to Frame Relay encapsulation.
• ATM—Operation, Administration, and Maintenance (OAM) and Interim Local Management Interface (ILMI) processing is terminated at the router. Cell relay is not supported. The JUNOS software strips all ATM encapsulation data from incoming frames before forwarding them. For output, the next hop is changed to ATM encapsulation.