This is the behavior of the original Napster client. With the Napster protocol in the public domain, new clients can behave however they want, including allowing users to specify the addresses of their own servers.
If the original Napster client hardcoded the hostname of the "server server" and not the IP address, it's trivial to associate a different IP address with that hostname (see/etc/hosts).
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If the original Napster client hardcoded the hostname of the "server server" and not the IP address, it's trivial to associate a different IP address with that hostname (see /etc/hosts).