Notizen:
The sequence number offers additional security against so called replay attacks. In a replay attack the attacker record correctly authenticated packets and replays them at a later point in time.
To protect the client sends each packet using an monotonously incremented sequence number.
The recipient may check the sequence number. It uses a sliding window of either 32 or 64 (recommend) packets. The recipient expects a packet with a sequence number n to n+63. If the packet has a sequence number smaller it will be dropped. If it has a sequence number larger n+63 and the packet is authenticated correctly the sliding window will be moved to accommodate the new sequence number.