I have an application that is running when directed hit using websphere application server(using the default port of the app server). What I want is that the application should be accessed using the iPlanet web server available.
I need to know the changes to be made to config files of the web server or app server concerned. Also do I need to make changes in obj.conf config file of iPlanet Web Server.
If you look at WAS Software Requirements page it refers to Sun Java System Web Server and I'm not sure that it match iPlanet product.
If it is supported you could administer it as other web server see: Administering web servers from the administrative console
Otherwise, it could be quite quite difficult to use iPlanet as HTTP Server. In fact, you can configure iPlanet to behave as a Reverse Proxy to route some HTTP requests (e.g. /yourapp/*) to WAS but you need to add a configuration for each app.
Moreover, if you have a WAS cluster, you will lose session affinity that is a capability of HTTP plugin provided by WAS: Configuring simple load balancing across multiple application server profiles.
I suggest you to use Web Server supported by WAS like IBM HTTP Server (the license is included in WAS)