Which statement describes IPv6 Path Discovery?

• A. It uses ICMP Echo Request messages to verify reachability
• B. This sends ICMPv6 'Packet Too Big' message with MTU size
• C. It discovers routes using Redirect messages
• D. It broadcasts Router Solicitation messages

Answer: (B)

Path MTU discovery in IPv6 relies on ICMPv6 Packet Too Big messages. When a packet is larger than what some link along the path can forward, a router returns an ICMPv6 Packet Too Big message that includes the MTU value for the next hop. The sender uses that MTU to shrink subsequent packets and tries again, continuing this process until delivery succeeds. In IPv6, routers don’t fragment packets; only the source does, so learning the path MTU is essential to avoid fragmentation. The other described activities—using an Echo Request to check reachability, Redirect messages for route changes, or soliciting routers—do not describe how path MTU discovery works.