Sun Java System Web Server 6.1 supports the Servlet 2.3 specification.
Netscape Enterprise Server iPlanet Web Server 4.0 and 4.1 supported the Java Servlet 2.1 specification. This specification did not include web applications. A deployment scheme was developed to make servlet deployment simpler. With the advent of Java Web Applications (.war files) and their deployment descriptors, it is no longer necessary to maintain a proprietary deployment system.
iPlanet Web Server 6.0 supported both types of deployment schemes, but the 4.x implementation (referred to as legacy servlets) was marked as deprecated (See Chapter 8: “Legacy Servlet and JSP Configuration” of the iPlanet Web Server, Enterprise Edition Programmer's Guide to Servlets).
Sun Java System Web Server 6.1 does not support Legacy Servlets. The legacy-style properties files for the server you want to migrate - servlet.properties, context.properties, and rules.properties - are removed during migration.
Because there is no one-to-one mapping for all of the features, legacy servlets cannot be migrated automatically.
For documentation and samples to help you migrate your 4.x legacy-style servlets to the web applications structure in Sun Java System Web Server 6.1, see the Sun Java System Web Server 6.1 SP10 Programmer’s Guide to Web Applications.