Systat (protocol)

Systat or Active Users is a simple Internet protocol ostensibly useful for "debugging and measurement".

{{cite IETF

| last = Postel

| first = J.

| title = Active Users

| rfc = 866

| publisher = IETF

|date=May 1983

}}

A connection to port 11, by either TCP or UDP, elicits a list of users currently logged into the system. Though it remains an official Internet protocol, its use is considered a security vulnerability.{{cite web

|url=http://etutorials.org/Networking/network+security+assessment/Chapter+5.+Assessing+Remote+Information+Services/5.2+systat+and+netstat/

|title=systat and netstat

|publisher=eTutorials

}}