System Administration Guide: Network Services

nfsmapid and DNS TXT Records

The ubiquitous nature of DNS provides an efficient storage and distribution mechanism for the NFS version 4 domain name. Additionally, because of the inherent scalability of DNS, the use of DNS TXT resource records is the preferred method for configuring the NFS version 4 domain name for large deployments. You should configure the _nfsv4idmapdomain TXT record on enterprise-level DNS servers. Such configurations ensure that any NFS version 4 client or server can find its NFS version 4 domain by traversing the DNS tree.

The following is an example of a preferred entry for enabling the DNS server to provide the NFS version 4 domain name:

_nfsv4idmapdomain		IN		TXT			""

In this example, the domain name to configure is the value that is enclosed in double-quotes. Note that no ttl field is specified and that no domain is appended to _nfsv4idmapdomain, which is the value in the owner field. This configuration enables the TXT record to use the zone's ${ORIGIN} entry from the Start-Of-Authority (SOA) record. For example, at different levels of the domain namespace, the record could read as follows:    IN    TXT    ""           IN    TXT    ""

This configuration provides DNS clients with the added flexibility of using the resolv.conf file to search up the DNS tree hierarchy. See the resolv.conf(4) man page. This capability provides a higher probability of finding the TXT record. For even more flexibility, lower level DNS sub-domains can define their own DNS TXT resource records (RRs). This capability enables lower level DNS sub-domains to override the TXT record that is defined by the top level DNS domain.

Note –

The domain that is specified by the TXT record can be an arbitrary string that does not necessarily match the DNS domain for clients and servers that use NFS version 4. You have the option of not sharing NFS version 4 data with other DNS domains.