SSH Concurrent Session Fails - Error “ssh_exchange_identification: read: Connection reset by peer"

Applies to:

Oracle Cloud Infrastructure - Version N/A and later

Linux x86-64

Symptoms:

Unable to do concurrent SSH sessions from on-premises to OCI Linux instance or between OCI instances from different VCN subnets, over a certain maximum number of connections:

$ for ((i=1;i<=100;i++)); do echo ${i};  ssh -i /home/opc/.ssh/id_rsa opc@x.x.x.x uptime > /dev/null; done
 1
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 8
 9
 …
 19
 20
ssh_exchange_identification: read: Connection reset by peer21
ssh_exchange_identification: read: Connection reset by peer22
ssh_exchange_identification: read: Connection reset by peer23
ssh_exchange_identification: read: Connection reset by peer24
ssh_exchange_identification: read: Connection reset by peer25
ssh_exchange_identification: read: Connection reset by peer26
ssh_exchange_identification: read: Connection reset by peer27