Masters and Replicas

Only NIS+ masters are allowed to write data to LDAP. NIS+ replicas can obtain updates either from the NIS+ master (which might or might not have obtained it from LDAP), or they can read data directly from an LDAP server. A combination of the two is also possible. Therefore, there are two principal ways to arrange for NIS+ replication.

• Leave NIS+ replicas unchanged, and let them obtain their data updates from the NIS+ master.

  This arrangement has the advantage of configurational simplicity (only the NIS+ master need have a connection to an LDAP server), and also maintains the old replication relationship (master knows about new data first, replicas later). It is probably the most convenient solution while NIS+ remains authoritative for naming service data. However, it also lengthens the path between LDAP and NIS+ replica servers.

• Let NIS+ replicas obtain their data directly from LDAP instead of from the NIS+ master.

  In this case, replicas could have updated data before or after the NIS+ master, depending on lookup traffic and TTLs for data derived from LDAP. This arrangement is more complicated, but can be convenient when LDAP is the authoritative naming services repository, and few or no updates are made directly to NIS+ data.

Replication Timestamps

When an NIS+ replica is obtaining data for at least one object in a particular NIS+ directory from LDAP, the update timestamps printed by nisping(1M) do not necessarily indicate the degree of data consistency between the NIS+ master and the replica. For example, assume that the NIS+ directory dir1 contains the tables table1 and table2. When the replica is obtaining data for both table1 and table2 from the NIS+ master, you might see an output like the following.

# nisping dir1

Master server is "master.some.domain."
Last update occurred at Mon Aug  5 22:11:09 2002

Replica server is "replica.some.domain."
	Last Update seen was Mon Aug  5 22:11:09 2002

The above indicates that the master and replica have exactly the same data. However, if the replica is getting data for either or both of table1 and table2 from LDAP, the output only shows that the replica has received an NIS_PING from the master, and updated its resynchronization time stamp for housekeeping purposes. The data in the table or tables mapped from LDAP might differ from that on the NIS+ master if either of the following are true.

• The LDAP data differs from that on the NIS+ master.

• The replica has data in its cache (its local version of the NIS+ database) that has not expired, but that is not up to date with LDAP.

If you cannot accept this type of data inconsistency, let all NIS+ replicas obtain their data from the NIS+ master only. Once you have configured the NIS+ master to get data from LDAP, you do not need to make modifications to the replicas.

The Directory Server

The LDAP mapping portion of the rpc.nisd daemon uses LDAP protocol version 3 to talk to the LDAP server. The default mapping configuration (/var/nis/NIS+LDAPmapping.template) expects that the LDAP server supports an extended version of RFC 2307. RFCs can be retrieved from http://www.ietf.org/rfc.html. While the mapping between NIS+ and LDAP data can be modified using NIS+LDAPmapping(4), there is a basic assumption that the LDAP data is organized along the principles laid out in RFC 2307.

For example, in order to share account information between direct LDAP clients and NIS+ clients, the LDAP server must support storing account (user) passwords in the UNIX crypt format. If the LDAP server cannot be configured to do so, you can still store NIS+ data, including accounts, in LDAP. However, you will not be able to fully share account information between NIS+ users and LDAP bindDNs.

Configuring the Sun ONE Directory Server

Refer to the Sun ONE Directory Server Collection for detailed instructions on the installation, setup and administration of Sun ONE Directory Server.

You can use idsconfig(1M) to configure Sun ONE Directory Server for LDAP clients using LDAP as a naming service. The setup provided by idsconfig(1M) is also appropriate when using NIS+ with an LDAP data repository.

Note - If you are using an LDAP server other than Sun ONE Directory Server, you must manually configure the server to support the RFC 2307 schemas.

Assigning Server Address and Port Number

The /etc/default/rpc.nisd file is set up to use a local LDAP server at port 389. If this is not correct in your configuration, establish a new value for the preferredServerList attribute. For example, to use an LDAP server at IP address 192.0.0.1 and port 65535, you specify the following.

preferredServerList=192.0.0.1:65535

Security and Authentication

Authentication between NIS+ clients and the NIS+ server is not affected when the NIS+ server is obtaining data from LDAP. However, in order to maintain the integrity of the NIS+ data when it is stored in LDAP, consider configuring authentication between the rpc.nisd daemon and the LDAP server. Several different types of authentication are available, depending on the capabilities of the LDAP server.

The LDAP authentication supported by the rpc.nisd daemon includes the following.

• none

  The none authentication method is the default. While using none requires no setup, it also provides no security. It is only suitable for use in environments that have no security requirements at all.

  To use the none authentication, make sure that the authenticationMethod attribute has the following value.

  authenticationMethod=none

  
  

The authentication methods that actually provide at least some security typically require that you associate a shared secret (a password or key) with a DN in LDAP. The DN you select for use by the rpc.nisd daemon can be unique, or can also be used for other purposes. It should have appropriate capabilities to support the expected LDAP traffic. For example, if the rpc.nisd daemon should be able to write data to LDAP, the selected DN must have the right to add/update/delete LDAP data in the containers used for the NIS+ data. Also, the LDAP server might, by default, impose limitations on resource usage (such as search time limits or search result size limitations). If this is the case, the selected DN must have sufficient capabilities to support enumeration of the NIS+ data containers.

• simple

  The simple authentication method provides authentication by unencrypted exchange of a password string. Since the password is sent in the clear between the LDAP client (the rpc.nisd daemon) and LDAP server, the simple method is suitable only when information exchange between the NIS+ and LDAP servers is protected by some other method.

  For instance, transport layer encryption of LDAP traffic, or the special case where the NIS+ and LDAP server is one and the same system, and the NIS+/LDAP traffic stays in the kernel, protected from the eyes of unauthorized users.

  Modify the configuration of the rpc.nisd daemon with the DN and password to use for the simple authentication. For example, if the DN is cn=nisplusAdmin,ou=People,dc=some,dc=domain, and the password aword, establish the following.

  authenticationMethod=simple nisplusLDAPproxyUser=cn=nisplusAdmin,ou=People,dc=some,dc=domain nisplusLDAPproxyPassword=aword

  
  

  Be sure to protect the place where the password is stored from unauthorized access. Remember that if the password is specified on the rpc.nisd command line, it might be visible to any user on the system via commands such as ps(1).

• sasl/digest-md5

  The sasl/digest-md5 authentication method provides authentication using the digest/md5 algorithm.

  Consult your LDAP server documentation for information on how to set up an authorization identity for use with digest-md5, and modify the /etc/default/rpc.nisd file to specify this identity and its associated password.

  authenticationMethod=sasl/digest-md5 nisplusLDAPproxyUser=cn=nisplusAdmin,ou=People,dc=some,dc=domain nisplusLDAPproxyPassword=aword

  
  

  Be sure to protect the file where the password is stored from unauthorized access.

• sasl/cram-md5

  Authentication using the cram/md5 algorithm. Probably only supported by the obsolete SunDS LDAP server.

  Consult your LDAP server documentation for information on how to set up a bind DN for use with cram-md5, and modify the /etc/default/rpc.nisd file to specify this DN and its associated password.

  authenticationMethod=sasl/cram-md5 nisplusLDAPproxyUser=cn=nisplusAdmin,ou=People,dc=some,dc=domain nisplusLDAPproxyPassword=aword

  
  

  Be sure to protect the file where the password is stored from unauthorized access.

Using SSL

The rpc.nisd daemon also supports transport layer encryption of LDAP traffic using SSL. Consult your LDAP server documentation to generate an SSL certificate for LDAP server authentication. Store the certificate in a file on the NIS+ server (/var/nis/cert7.db, for example) and modify /etc/default/rpc.nisd as follows.

nisplusLDAPTLS=ssl
nisplusLDAPTLSCertificateDBPath=/var/nis/cert7.db

Be sure to protect the certificate file from unauthorized access. Note that the above provides session encryption and authentication of the LDAP server to the rpc.nisd. It does not provide authentication of the rpc.nisd to the LDAP server, since the certificate does not contain anything that identifies the LDAP client (rpc.nisd). However, you can combine SSL with another authentication method (simple, sasl/digest-md5) in order to achieve mutual authentication.