IPSEC Encapsulating Security Payloads (ESP)
Organized in 32 bit words the format is as follows:
- Security Parameters Index (SPI) - Word 0
- Sequence Number Field - Word 1
- A variable amount of payload data.
- 0-255 bytes of padding
- 8 bits of pad length
- 8 bits of next header
- A variable amount of authentication data.