When you deploy a simple secure webapp on a v3.1 cluster with iPlanet WebServer with LB plugin frontend, and access the webapp using HTTPS, it redirected to GF instance HTTPS port. In this setup, neither HTTPS Routing not authPassThrough is enabled. With this its exposing the GF instance to the client.
For ex: When I access https://webserver_host/WebApplliaction/index.jsp it redirects to https:gf_instancehost_port/WebApplciation/index.jsp.
Because of the SSL offloading, the HTTPS request from client is forwarded by the LB to the HTTP port of the GF instance. Its reasonable that GF instance sees this request as received on unsecure port and redirects to secure port. But it should have redirected to the WebServer HTTPs port using the Host header in the incoming request.
As per analysis done by Kshitiz, GF instance seems to use the host name from Host header, However ssl port for instance is appended to it which is incorrect.