"Cannot assign requested address" (EADDRNOTAVAIL) when many TCP sessions are open

Issue

• "Cannot assign requested address" (EADDRNOTAVAIL) when many TCP sessions are open
• On systems running RHEL6 or RHEL7, when a large number of ESTABLISHED state connections (over 1 million) are open, then one sees errors where unrelated processes (curl, ssh, etc) are unable to bind to a local IP on the box to initiate a connection. For example, trying to execute curl to connect to a remote server, it fails with

curl: (7) Failed to connect to 10.0.0.1: Cannot assign requested address".

• This works successfully and consistently below approximately 1 million established connections, but fails consistently when above that number.
• However, if the application explicitly specifies the local IP to be used, then commands succeed.