De-duplication for IPv6
IPv6 lacked a critical field available in IPv4 which was used for diagnostics. This was the IPID which acted as a de-facto IP sequence number. EDCO was able to have a draft adopted jointly by the IP Performance Metrics (IPPM) and IPv6 Maintenance (6man) Working Groups of the IETF. Our standard defines a new Performance and Diagnostics (PDM) header for IPv6. Our goal is to have this header flow in every IPv6 packet on the Internet. Click HERE to see the standard.
An IP sequence number is critical for the following reasons:
Separating multiple TCP retransmissions
Detecting packet loss
Separating duplicate packets from retransmissions
Seeing if the trace capture is valid
Large data trace capture devices have used the IPID field for de-duplication for IPv4. This field was not available in IPv6. See below for a screen shot for an IPv6 FTP without our PDM Sequence number. This is
what you would get "normally".
With our new standard: PDM, you have the following:
The PDM sequence number is especially helpful for protocols such as UDP which do not have a sequence number. The problem with TCP sequence and ACK is that the sender may send 7 retransmissions but only 3 get through.There is no way to tell that without a sequence number at the IP level. The TCP sequence and ACK will appear exactly the same in each packet. When taking a trace capture using large packet trace capture devices, packets may be duplicated or merged from duplicate points. With only a TCP sequence number, it is impossible to tell if the packets are valid duplicates / retransmissions or a problem with the data capture. PDM will become more and more important as many of the new implementations of IP protocols, such as in cars and drones, may use IPv6 exclusively.