Take stock of your NIS servers, keeping in mind the requirements for your NIS+ servers. If you plan to eventually use them for the NIS+ service, upgrade them to the NIS+ recommendations. Identify which NIS servers will be used to support which NIS+ domains, and in what capacity (either master or replica). Remember that NIS+ servers belong to the domain above the one they support (except for the root domain servers). Since NIS+ servers do not belong to the domain they serve, you cannot use the same machines for other services that require domain-dependent information.
If possible, plan to use your NIS+ server machines only for NIS+. This arrangement can require you to transfer other network services, such as DNS name services, boot server, home directories, NFS servers, and so on, to non-NIS+ server machines.
At many sites, the NIS server plays multiple roles, such as NFS server, compute server, rlogin server, and mail host server. Because the NIS server uses the same information to resolve its names as do its clients, the NIS server can provide other services as well. As discussed in "Domain Hierarchy", except for root domains, all NIS+ servers live in the domain above the ones that they serve. So either do not run services on an NIS+ server that require access to the name service, or use other means, such as files in nsswitch.conf, to acquire this same information. This problem would be solved if there were no hierarchy; the NIS+ root servers would live in the domain that they serve. The resource requirements of an NIS+ server are greater than those of an NIS server; therefore, it is advisable to avoid running other services along with NIS+.
If you have non-Solaris machines on your network, then you can either continue to run your NIS+ servers in NIS-compatibility mode or you can move all such machines into their own domain. If you move all non-Solaris machines to one subnet, you can remove the restriction of having NIS+ servers on the same subnet as their NIS-compatible clients. This will reduce the number of replicas required for any domain.