Padding
Most encryption algorithms require that the input data must be an integral number of blocks. The resulting ciphertext (which includes the Padding, Pad Length, and Next Header fields) have to terminate on a 4-byte boundary. This is so that the Next Header field is right aligned. Padding is an optional field, so whatever cipher is used, it has a field to insure correct alignment.

Pad Length
This 8-bit field contains the number of the preceding padding bytes. It is always present, and the value of 0 indicates no padding.

Next Header
The Next Header is an 8-bit mandatory field that shows the data type carried in the payload. The data type is one of those on the IP Protocol Numbers List.