Use a random initial sequence number for IO connections and check for a sequence number gap

When targets and originators begin producing data on a transport class 0 or 1 connection, a
random initial Encapsulation Sequence Number shall be used.
In addition, Packets shall be discarded if the Encapsulation Sequence Number is greater than the last
received and accepted Encapsulation Sequence Number plus the Allowed Sequence Number
Gap. For more information see CIP Volume 2 Edition 1.17 Chapter 3-4.1 "CIP Transport Class 0 and Class 1 Packet Ordering".