On interfaces with Frame Relay CCC encapsulation, you can configure Frame Relay control bit translation, as defined in the IETF documents:
To support Frame Relay services over IP and MPLS backbones using Layer 2 VPNs and Layer 2 circuits, you can configure translation of the Frame Relay control bits. When you configure translation of Frame Relay control bits, the bits are mapped into the Layer 2 circuit control word and preserved across the IP or MPLS backbone.
The JUNOS software allows you to translate the following Frame Relay control bits:
By default, translation of Frame Relay control bits is disabled. If you enable Frame Relay control bit translation, the bits are translated in both directions (CE to PE and PE to CE):
The Frame Relay control bits do not map to MPLS EXP labels, and do not affect class-of-service (CoS) behavior inside the provider network.
You enable or explicitly disable translation of Frame Relay control bits by including the translate-discard-eligible and translate-fecn-and-becn statements:
- (translate-discard-eligible | no-translate-discard-eligible);
- (translate-fecn-and-becn | no-translate-fecn-and-becn);
You can include these statements at the following hierarchy levels:
If you enable or disable Frame Relay control bit translation on one CE-facing interface, you must configure the same Frame Relay control bit translation settings on the other CE-facing interface.
If you change the Frame Relay control bit translation settings, the circuit goes down and comes back up, which might result in traffic loss for a few seconds.
If you enable Frame Relay control bit translation, the number of supportable Layer 2 virtual private networks (VPNs) and Layer 2 circuits is reduced to one eighth of what the routing platform can support without Frame Relay control bit translation enabled.
For ATM2 IQ interfaces, the control word contains a field to carry ATM cell loss priority (CLP) information by default. For more information, see Configuring Layer 2 Circuit Transport Mode.
For more information about Layer 2 circuits, see the JUNOS VPNs Configuration Guide and the JUNOS Routing Protocols Configuration Guide. For a comprehensive example, see the JUNOS Feature Guide.