Interoperable Frame Relay to non-Cisco peer: Which encapsulation command should be set on the Cisco WAN interface?

Introduction / Context:
Frame Relay encapsulation has vendor-specific and standards-based variants. When peering with non-Cisco devices, selecting the interoperable framing ensures successful data exchange.

Given Data / Assumptions:

• You are configuring a Cisco router's serial interface for Frame Relay.
• The remote DTE is a non-Cisco device.
• Goal: choose an encapsulation that works across vendors.

Concept / Approach:
Cisco supports 'frame-relay cisco' (proprietary) and 'frame-relay ietf' (standards-based, RFC 1490/2427). For interoperability with other vendors, use the IETF encapsulation. ANSI or q933a refer to LMI types (signaling), not payload encapsulation.

Step-by-Step Solution:

Verification / Alternative check:
Show interface after configuration should display 'Encapsulation FRAME-RELAY IETF'; data then exchanges with third-party peers correctly.

Why Other Options Are Wrong:
frame-relay cisco: Proprietary encapsulation, not recommended for multi-vendor links.
ansi/q933a: LMI types, not encapsulation. They govern status messages with the switch, not payload framing.

Common Pitfalls:
Confusing LMI type with encapsulation; both may need configuration, but only 'ietf' addresses the multi-vendor payload format.

Final Answer:
Router(config-if)#encapsulation frame-relay ietf