There's no such thing as a duplicate packet. Older protocols may very well send keepalives as a (UDP) packet that repeatedly has the same contents. Removing/d

There's no such thing as a duplicate packet. Older protocols may very well send keepalives as a (UDP) packet that repeatedly has the same contents. Removing/dropping such packets is not something a router is "allowed" to do. Also, apart from that, all but the smallest routers do not look at the actual data packets. They set up some rules for what they want (i.e. traffic addressed to them, routing protocols, some ICMP, etc.) and everything else never leaves the hardware forwarding pipe. Last I checked, a fat x86 box clocks in at a few 100Gb/s of software forwarding while hardware routers are breaking the 10Tb/s barrier easily. [Ed. to add:] Actually, if something further down behind your "deduplicating" router is overloaded/dropping packets, plain TCP will resend the lost packets with little to no changes. If the deduplication drops the retransmits, you've now broken plain current TCP ;). And having dropped packets & retransmits is a fundamental part of how TCP congestion control works (less so with ECN, but still.)