Server-Use Customization

This chapter describes how to customize and control which servers NIS+ clients use.

Note - NIS+ might not be supported in a future release. Tools to aid the migration from NIS+ to LDAP are available in the Solaris 9 operating environment (see System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP)). For more information, visit http://www.sun.com/directory/nisplus/transition.html.

NIS+ Servers and Clients

When client machines, users, applications, or processes need NIS+ information, they seek an active NIS+ server (master or replica) from which to get the needed data. On large networks, networks with many subnets, and networks that span wide-area links, you may be able to improve NIS+ performance by customizing server usage.

Default Client Search Behavior

By default, if no server preferences have been set with the nisprefadm command, a client will first try to obtain the information it needs from an NIS+ server on the client's local subnet. If the client finds an active server on the local subnet, it obtains the information it needs from the first local server that responds. If no server is available on the local subnet, the client searches outside the local subnet, and obtains the NIS+ information it needs from the first remote server that responds.

On large, busy networks, this default search behavior may reduce NIS+ performance for one of two reasons:

• When multiple servers on a subnet are serving a large number of clients, the random nature of the client's default search pattern may result in some servers being over worked while others are under used.

• When a client has to seek an NIS+ server beyond the local subnet, it will obtain its information from the first server that responds even if that server is overworked, or linked to the client's subnet by a slower Wide Area Network connection such as a modem or a dedicated line that is already carrying heavy traffic.

Designating Preferred Servers

The Solaris operating environment contains a new feature--server-use customization--that allows you to control the order in which clients search for NIS+ servers. With this new feature you can balance and customize server usage by:

• Specifying that clients prefer (search for) certain servers over others.

• Specify whether or not clients are permitted to use remote servers if no local servers are available.

The search criteria that you specify can be applied to all clients within a domain, all clients on a subnet, or to individual clients on a machine-by-machine basis.

Note - When server-use preferences are set for a particular machine, those preferences apply to all users, applications, processes, or other clients running on that machine. You cannot set different server-use patterns for different clients on the same machine.

NIS+ Over Wide Area Networks

Server-use customization is particularly valuable for large networks with many subnets and networks that span multiple geographic sites connected by modems or leased lines. To maximize network performance, you want to minimize network traffic between subnets, and between sites linked by slower connections. You can do that by specifying which NIS+ servers the clients can use, and their order of server preference. In this way you confine as much NIS+ network traffic as possible to the local subnet.

Optimizing Server-Use--Overview

This section provides an overview of server-use customization.

nis_cachemgr is Required

Server-use customization requires that a client be running nis_cachemgr. If a client machine is not running nis_cachemgr, it cannot make use of server-use customization. If there is no nis_cachemgr running on a client machine, that client will use the first server it identifies as described in Default Client Search Behavior.

Global Table or Local File

Depending on how you use the nisprefadm command, it creates either a local client_info file or a domain client_info table:

• File. You can use nisprefadm to create a local, machine-specific client_info file that is stored in the machine's /var/nis directory. A local file specifies server preferences for that machine only. When a machine has a local /var/nis/client_info file, it ignores any server preferences contained in a domain client_info.org_dir table. To create a local client_info file, you run nisprefadm with the -L option.

• Table. You can use nisprefadm to create an NIS+ client_info table which is stored in each domain's org_dir NIS+ directory object. This table can specify server preferences for:

  • Individual machines. (If a machine has a local /var/nis/client_info file, any preferences for that machine that happen to be in the domain client_info table are ignored.)

  • All the machines on a particular subnet. (If a machine on the subnet has a local /var/nis/client_info file or individual preferences set for it in the table it ignores subnet preferences.)

  To create a global client_info table that applies to all machine on a subnet, you run nisprefadm with the -G and -C options as described in Specifying Global Server Preferences.

  Note that if a machine has its own local client_info file as described below, it will ignore all server preferences set for it in a global client_info table. If a machine has either a local client_info file or a machine-specific entry for it in the global client_info table, it will ignore preferences set for its subnet.

Caution - Use only the nisprefadm command to make changes to client_info files and tables. Never use other NIS+ commands such as nistbladm.

When working with client_info tables or files, you must use either the -G or the -L option to specify that your command apply to either the global table (-G) or local file (-L) of the machine you are running the command on.

Preference Rank Numbers

Server preferences are controlled by giving each server a preference rank number. Clients search for NIS+ servers in order of numeric preference, querying servers with lower preference rank numbers before seeking servers with higher numbers.

Thus, a client will first try to obtain namespace information from NIS+ servers with a preference of zero. If there are no preference=0 servers available, then the client will query servers whose preference=1. If no 1's are available, it will try to find a 2, and then a 3, and so on until it either gets the information it needs or runs out of servers.

Preference rank numbers are assigned to servers with the nisprefadm command as described in Specifying Global Server Preferences.

Server preference numbers are stored in client_info tables and files. If a machine has its own /var/nis/client_info file, it uses the preference numbers stored in that file. If a machine does not have its own client_info file, it uses the preference numbers stored in the domain's client_info.org_dir table. These client_info tables and files are called "preferred server lists" or simply server lists.

You customize server usage by controlling the server preferences of each client. For example, suppose a domain has a client machine named mailer that makes heavy use of namespace information and the domain has both a master server (nismaster) and a replica server (replica1). You could assign a preference number of 1 to nismaster and a number of 0 to replica1 for the mailer machine. The mailer machine would then always try to obtain namespace information from replica1 before trying nismaster. You could then specify that for all the other machines on the subnet the nismaster server had a preference number of zero and replica1 the number 1. This would cause the other machine to always try nismaster first.

You can give the same preference number to more than one server in a domain. For example, you could assign both nismaster1 and replica2 a preference number of 0, and assign replica3, replica4, and replica5 a preference number of 1.

Default Server Preferences

If there is no client_info file or table, the cache manager automatically assigns all servers on the local subnet a default preference number of zero (0) and all servers outside the local subnet a preference of infinite. The purpose of nisprefadm is to change these default preference numbers to what you want them to be.

Efficiency and Server Preference Numbers

A client must seek all servers with a given preference number before searching for servers with the next higher number. It requires 5 or more seconds for a client to search for all the servers with a given preference number. This means that if you have a master server and 4 replicas in a domain, and you give each one a different preference number from 0 to 4, it could take a client more than 25 seconds to run through all of those preference levels.

To maximize performance, you should not use more than two or three levels of server preference. For example, in the case described above, it is better to give one of those five servers a preference=0 and all the others a preference of 1, or give two of them a preference of 1 and the remaining three a preference of 2.

Preferred Only Servers Versus All Servers

Server lists also specify what a client does if it cannot find any preferred servers. A preferred server is any server with a preference of zero, or any server that you have assigned a preference number with nisprefadm.

By default, if a client fails to reach a preferred server, it will then seek out any server it can find anywhere on the network using the search mode described in Default Client Search Behavior. You can change this default behavior with the nisprefadm -o option to specify that a client can only use preferred servers and if no servers are available it cannot go to non-preferred servers. See Specifying Preferred-Only Servers for details.

Note - This option is ignored when the machine's domain is not served by any preferred servers.

Viewing Preferences

To view the server preferences currently in effect for a particular client machine, you run nisprefadm with the -l option as described in Viewing Current Server Preferences.

Server and Client Names

When specifying server or client machines, keep in mind the following points:

• Server and client names do not need to be fully qualified so long as they are in the same NIS+ domain and uniquely identify the object. You can simply use the machine name by itself.

• If a server or subnet is in another NIS+ domain, you need to include enough of the domain name to uniquely identify that machine. For example, if you are in the sales.doc.com domain and you need to specify the nismaster2 machine in the manf.doc.com domain, you need only enter nismaster2.manf.