= The Schema Compatibility Plugin in IPA =

RFC 2307 defines object classes and attributes suitable for representing
various POSIX-related information in a directory.  The "posixGroup"
object class, for example, models a group of accounts, including the
POSIX group's ID (as the value of the "gidNumber" attribute) and the
names of each of the members of the group (as values of the "memberUid"
attribute).

This representation is supported by the native LDAP client software
supplied with a number of Unix and Unix-like operating systems.

The draft revision of RFC 2307, known as "rfc2307bis", modifies the
contents of a group so that it no longer contains the names of its
members in the "memberUid" attribute, but rather uses the "member"
attribute to list the distinguished names of the entries which represent
the individual members.  A client is typically expected to search the
named entries to determine the names of the group's member users.

It is this representation of groups which FreeIPA and RHEIPA use.

This representation is not as well-supported by the native LDAP client
software supplied with Unix and Unix-like operating systems.

When configured to consult a server which stores information this way, a
client which does not support reading group membership from the "member"
attribute will still able to look up a group and read its name and ID,
but will be unable to "see" the members of the group.

For these clients, an IPA server can be configured to use the Schema
Compatibility Plugin to resolve the group membership at the server.  The
plugin will examine the group entries stored in the server and, as
configured, read the distinguished names of the members of those groups.
It will examine the named entries and read from them the names of the
members of the group.  It will then use that data to create an in-memory
entry, elsewhere in the directory tree, which contains the group
membership information in a form which the client is able to process.

As configured, an IPA server provides this information, for groups whose
entries are beneath "cn=groups, cn=accounts, $SUFFIX", in an area
beneath "cn=groups, cn=compat, $SUFFIX".