When IP Duplication is made?

I developed TCPIP stack concerned program … during many years.  and I implemented IP Duplication Checking Logic. Just Checked IP identification is same or not when 2 tuple( source IP, Destination IP)  is *same. But… I didn’t think about it in detail. “When IP Duplication is invoked?”

* IP Identification Field. – It is kinds of Unique-Sequence number on Same Source-Destination IP.

First. I can’t find any clues  about  “IP Duplication case” in IP Header .and I could find TCP Duplication easily but. Not easy to find “IP Duplication case”.

but. Finally

https://tools.ietf.org/html/rfc6864#section-3.1

you can find this …

Other uses have been envisioned for the IPv4 ID field.  The field has
   been proposed as a way to detect and remove duplicate datagrams,
   e.g., at congested routers (noted in Section 3.2.1.5 of [RFC1122]) or
   in network accelerators.  It has similarly been proposed for use at
   end hosts to reduce the impact of duplication on higher-layer
   protocols (e.g., additional processing in TCP or the need for
   application-layer duplicate suppression in UDP).  This is discussed
   further in Section 5.1.

please check these words.. ‘congested router’ , ‘network accelerators’..

Could you guess  ‘congested router’ , ‘network accelerators’. how it works? I will avoid to mention about details about this device. but .. I assume they have buffer for control packets.

“Having Buffer” means it can make copied packet for more faster.. for more reliable .do you make sense ? … Yes. these kind of network device can send same packet again and again if They found have some problem of sending packet… But sent packet could reach destination even though that packet are considered as wrong packet.. because.. Receiver (deliver) cant know this packet is wrong or not…just will process it.

So. on TCPIP Stack Implementation. IP Duplication Checking is MUST.

That’s all… My Guess can be wrong in details.  but I convince that It almost right.  Sorry .. but My Recommendation is that You must think about it with your story if you hope to understand it.. and You will get the insight.

* IP identification  field on (Source/Destination IP is same ) can also same when IP packet is fragmented ( by Network Device which is located in Network Path ). It will also be written in the future.