IP has the ability to broadcast and multicast packets on the local network. Such packets are addressed to special broadcast and multicast addresses. Broadcast is used heavily in many UDP based protocols such as the Microsoft Windows file-sharing SMB protocol. Multicast is primarily used in protocols used for multimedia distribution such as RTP. TCP is a point-to-point protocol and does not use broadcast or multicast packets.
Because lwIP supports applications using UDP, it has support for both sending and receiving broadcast and multicast packets. In contrast, uIP does not have UDP support and therefore handling of such packets has not been implemented.