Briefly discuss four limitations of UDP.

What will be an ideal response?

No reliability mechanisms: Datagrams are not sequenced and are not acknowledged. Most applications or services that use UDP supply their own reliability mechanisms, or track timeout values for datagrams, and retransmit when a datagram's timeout counter expires.
No delivery guarantees: Datagrams are sent without any promise of delivery, so, again, the Application layer must provide tracking and retransmission mechanisms.
No connection handling: Each datagram is an independent message that the sender transmits without UDP providing any way to establish, manage, or close a connection between sender and receiver.
Identifies Application layer protocol conveyed: As noted previously, the UDP header includes fields that identify port addresses, also known as port numbers, for sending and receiving Application layer services or processes.
Checksum for entire message carried in UDP header:As packaged, each UDP header may optionally include a checksum value that can be recalculated upon delivery, and compared to the value as sent. It's up to the Application layer service or protocol to act on this information - UDP does nothing more than provide this data, and does not require that a checksum be calculated, per se.
No buffering services:UDP doesn't manage where incoming data resides in memory before delivery, or where outgoing data resides before transmission. All memory management for data in motion must be handled at the Application layer for services that use UDP; it sees strictly one datagram at a time.
No segmentation: UDP provides no services to break up arbitrarily large messages into discrete, labeled chunks for transmission, or to reassemble sequences of labeled chunks upon reception. UDP only sends and receives datagrams; the Application layer protocol or service must handle segmentation and reassembly, as required.