Cisco Arch Rock Corporation Considering that the IPv6 minimum MTU is 1280 bytes and that an an 802.15.4 frame can have a payload limited to 74 bytes in the worst case, a packet might end up fragmented into as many as 18 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 forward and recover individual fragments that might be lost over multiple hops between 6LoWPAN endpoints.