If a device has MBF, USIP, USNIP, and Layer 3 modes configured, which mode should be disabled to allow routing through a newly added router?

• A. Layer 3 mode
• B. USIP
• C. MAC-based Forwarding
• D. USNIP

Answer: (C)

Forwarding mode decisions determine whether the device uses IP routing or forwards purely by MAC on the local link. MAC-based Forwarding makes forwarding decisions based on destination MAC addresses, effectively bypassing the IP routing process. When a new router is added in the path, you want the device to participate in IP routing so packets follow the routing table to the next hop. Keeping MBF enabled would prevent that, because it would forward based on MAC rather than consulting the routing table. Disabling MAC-based Forwarding allows Layer 3 routing to take over, letting traffic go through the new router as intended. Layer 3 mode already supports routing; USIP and USNIP are other forwarding modes that aren’t required to disable to enable this routing path.