The Free On-line Dictionary of Computing (19 January 2023):

Automatic Network Routing
ANR

    (ANR) A source routing protocol used to route
   LU6.2 session and control traffic from node to node
   through a High Performance Routing network or subnet.  ANR
   operates at the lower end of the SNA Path Control layer.

   [Relationship to OS/390?]

   (1997-05-08)