userid prefixes

turned out to be Phone numbers belonging to PSI, UUNET. It was interesting
that the PPP Dial-up logon user ID was of the form: "ELN/userid" The
"ELN/" in front of the userid stands for Earthlink Network, so that
PSI/UUNET knows to which ISP to route the particular dial-up user.

  For what it's worth, the prefix (.*)/(.*) $1 is not relevant to
  the L3 routing of traffic (ie no P2TP tunnel or such) but rather
  is relevant to how the login is authenticated.

  The prefix tells the network access server (or the authentication
  infrastructure) to which authentication servers to send the login
  authentication request.