You are configuring a Cisco router for a Frame Relay connection to a non-Cisco router. Which encapsulation type should you configure on the Cisco router's WAN interface to ensure interoperability?

Introduction / Context:
Frame Relay is a Wide Area Network technology that supports virtual circuits between customer sites over a provider cloud. Cisco routers support different encapsulation types for Frame Relay. When connecting to another Cisco router, the default Cisco proprietary encapsulation is usually fine. However, when connecting to a non Cisco router, it is necessary to use a standards based encapsulation that both sides understand. Choosing the correct encapsulation ensures that Frame Relay headers are interpreted correctly and that data can be exchanged successfully.

Given Data / Assumptions:

• The local router is a Cisco device.
• The remote router is a non Cisco device.
• The technology in use is Frame Relay, not Point to Point Protocol or other WAN protocols.
• The encapsulation must be configured on the WAN interface of the Cisco router.

Concept / Approach:
Cisco routers support at least two Frame Relay encapsulation types: cisco and ietf. The cisco type uses a proprietary header format that is understood only by Cisco routers. The ietf type uses a header format that conforms to standards published by the Internet Engineering Task Force. Non Cisco routers that support Frame Relay are expected to understand the ietf encapsulation. Therefore, when interoperating with other vendors, the recommended choice is encapsulation frame-relay ietf on the Cisco side. This setting ensures interoperability at the Frame Relay header level.

Step-by-Step Solution:
1. Enter interface configuration mode for the relevant Wide Area Network interface, for example interface serial0/0. 2. Identify that the remote peer is a non Cisco router, which cannot use proprietary cisco Frame Relay encapsulation. 3. Use the encapsulation frame-relay command with the ietf keyword to specify standards based encapsulation. 4. The full command becomes Router(config-if)#encapsulation frame-relay ietf. 5. This configuration allows both routers to interpret Frame Relay headers correctly and exchange data over the virtual circuit.

Verification / Alternative check:
After configuring the interface, you can verify the encapsulation with show interfaces serial or show running-config interface. You should see encapsulation frame-relay ietf in the configuration. If the remote side is properly configured, Frame Relay Local Management Interface status will show as active, and pings between the sites will succeed. If the encapsulation types do not match, Local Management Interface may be active but data frames will not be interpreted correctly, leading to application failures.

Why Other Options Are Wrong:
Router(config-if)#encapsulation frame-relay q933a: This refers to a signalling standard and is not the correct keyword for Frame Relay data encapsulation on typical Cisco IOS routers.
Router(config-if)#encapsulation frame-relay ansi: This is also not the standard command keyword for Frame Relay encapsulation on Cisco routers in common certification scenarios.
Router(config-if)#encapsulation frame-relay cisco: This encapsulation is proprietary and works only between Cisco routers. It is not guaranteed to interoperate with non Cisco devices.
Router(config-if)#encapsulation frame-relay ppp: Point to Point Protocol is a completely different Layer two protocol. It is not used as a Frame Relay encapsulation type and the command syntax is invalid.

Common Pitfalls:
A common mistake is to leave the default encapsulation cisco in place when connecting to a non Cisco router. This often leads to confusion because Local Management Interface might still show a virtual circuit as up, but no user data flows correctly. Another pitfall is confusing standards like Q.933 with the encapsulation keyword, which are related but not used directly in the Cisco Frame Relay encapsulation command. To avoid these issues, always remember that ietf is the correct encapsulation keyword for interoperating with non Cisco routers in Frame Relay environments.

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