Cisco Considering that 6LoWPAN packets can be as large as 2K bytes and that an 802.15.4 frame with security will carry in the order of 80 bytes of effective payload, a packet might end up fragmented into as many as 25 fragments at the 6LoWPAN shim layer. If a single one of those fragments is lost in transmission, all fragments must be resent, further contributing to the congestion that might have caused the initial packet loss. This draft introduces a simple protocol to recover individual fragments between 6LoWPAN endpoints.