What does MTU stand for and what is Path MTU Discovery used for?

• A. Minimum Transmission Unit: Path MTU Discovery finds the smallest MTU on the path to avoid fragmentation.
• B. Maximum Transmission Unit: Path MTU Discovery finds the smallest MTU on the path to avoid fragmentation.
• C. Message Transmission Unit: Path MTU Discovery checks the maximum MTU on the path.
• D. Maximum Transfer Unit: Path MTU Discovery measures bandwidth between hosts.

Answer: (B)

MTU stands for Maximum Transmission Unit—the largest IP packet size that can be transmitted on a network link without fragmentation. Path MTU Discovery finds the smallest MTU along the route from source to destination, so packets can be sent at or below that size to avoid fragmentation across any hop. It uses mechanisms like the Don't Fragment bit and ICMP "Fragmentation Needed" messages to learn this limit. The goal isn’t to measure bandwidth or to use other terms like minimum or maximum in a different sense; MTU is about the maximum packet size, and PMTUD identifies the smallest such size on the path to prevent fragmentation.