TAP and IDENT are two alternative protocol specification for a successor to RFC931. The TAP protocol is a more "clean" protocol and doesn't include as many new "features" as IDENT does, but the basic functionality is more or less the same. If you don't use the extra features of the IDENT protocol (which has to be explicitly enabled in Pidentd), then it should be compatible. The TAP protocol is defined by a working group managed by Dan Bernstein. The IDENT protocol is defined by an IETF working group and is defined in RFC1413 that you may find at a number of sites, for example at: ftp.lysator.liu.se:pub/ident/doc/RFC1413 /Peter Eriksson , 3 Nov 1993