UDP HEADER

It consists of four fields each of 2 bytes in length –

Source Port(16 bits) –

This field identifies the sender’s port. Cleared to zero if not used.

Destination Port(16 bits) –

This field identifies the receiver’s port.

Length(16 bits) –

The length in bytes of the UDP header and the encapsulated data. The minimum value for this field is 8.

Checksum(16 bits) –

The checksum field may be used for error-checking of the header and data. This field is optional in IPv4, and mandatory in IPv6. The field carries all-zeros if unused. Needed with zero bytes at the end to make a multiple of two bytes. If the checksum is cleared to zero, then checksum is disabled. If the computed checksum is zero, then this field must be set to 0xFFFF.

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TCP HEADER