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NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION | ACCESS CONTROL | OVERLAYS | FILES | SEE ALSO | AUTHOR | COLOPHON |
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SLAPD-LDAP(5) File Formats Manual SLAPD-LDAP(5)
slapd-ldap - LDAP backend to slapd
ETCDIR/slapd.conf
The LDAP backend to slapd(8) is not an actual database; instead it
acts as a proxy to forward incoming requests to another LDAP
server. While processing requests it will also chase referrals, so
that referrals are fully processed instead of being returned to
the slapd client.
Sessions that explicitly Bind to the back-ldap database always
create their own private connection to the remote LDAP server.
Anonymous sessions will share a single anonymous connection to the
remote server. For sessions bound through other mechanisms, all
sessions with the same DN will share the same connection. This
connection pooling strategy can enhance the proxy's efficiency by
reducing the overhead of repeatedly making/breaking multiple
connections.
The ldap database can also act as an information service, i.e. the
identity of locally authenticated clients is asserted to the
remote server, possibly in some modified form. For this purpose,
the proxy binds to the remote server with some administrative
identity, and, if required, authorizes the asserted identity. See
the idassert-* rules below. The administrative identity of the
proxy, on the remote server, must be allowed to authorize by means
of appropriate authzTo rules; see slapd.conf(5) for details.
The proxy instance of slapd(8) must contain schema information for
the attributes and objectClasses used in filters, request DNs and
request-related data in general. It should also contain schema
information for the data returned by the proxied server. It is
the responsibility of the proxy administrator to keep the schema
of the proxy lined up with that of the proxied server.
Note: When looping back to the same instance of slapd(8), each
connection requires a new thread; as a consequence, the slapd(8)
threads parameter may need some tuning. In those cases, one may
consider using slapd-relay(5) instead, which performs the relayed
operation internally and thus reuses the same connection.
These slapd.conf options apply to the LDAP backend database. That
is, they must follow a "database ldap" line and come before any
subsequent "backend" or "database" lines. Other database options
are described in the slapd.conf(5) manual page.
Note: In early versions of back-ldap it was recommended to always
set
lastmod off
for ldap and meta databases. This was required because
operational attributes related to entry creation and modification
should not be proxied, as they could be mistakenly written to the
target server(s), generating an error. The current implementation
automatically sets lastmod to off, so its use is redundant and
should be omitted.
uri <ldapurl>
LDAP server to use. Multiple URIs can be set in a single
ldapurl argument, resulting in the underlying library
automatically calling the first server of the list that
responds, e.g.
uri "ldap://host/ ldap://backup-host/"
The URI list is space- or comma-separated. Whenever the
server that responds is not the first one in the list, the
list is rearranged and the responsive server is moved to
the head, so that it will be first contacted the next time
a connection needs to be created.
acl-bind bindmethod=simple|sasl [binddn=<simple DN>]
[credentials=<simple password>] [saslmech=<SASL mech>]
[secprops=<properties>] [realm=<realm>]
[authcId=<authentication ID>] [authzId=<authorization ID>]
[starttls=no|yes|critical] [tls_cert=<file>]
[tls_key=<file>] [tls_cacert=<file>] [tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_ecname=<names>]
[tls_protocol_min=<major>[.<minor>]]
[tls_crlcheck=none|peer|all]
Allows one to define the parameters of the authentication
method that is internally used by the proxy to collect info
related to access control, and whenever an operation occurs
with the identity of the rootdn of the LDAP proxy database.
The identity defined by this directive, according to the
properties associated to the authentication method, is
supposed to have read access on the target server to
attributes used on the proxy for ACL checking.
There is no risk of giving away such values; they are only
used to check permissions. The default is to use simple
bind, with empty binddn and credentials, which means that
the related operations will be performed anonymously. If
not set, and if idassert-bind is defined, this latter
identity is used instead. See idassert-bind for details.
The connection between the proxy database and the remote
server associated to this identity is cached regardless of
the lifespan of the client-proxy connection that first
established it.
This identity is not implicitly used by the proxy when the
client connects anonymously. The idassert-bind feature,
instead, in some cases can be crafted to implement that
behavior, which is intrinsically unsafe and should be used
with extreme care.
The TLS settings default to the same as the main slapd TLS
settings, except for tls_reqcert which defaults to
"demand", and tls_reqsan which defaults to "allow".
cancel {ABANDON|ignore|exop[-discover]}
Defines how to handle operation cancellation. By default,
abandon is invoked, so the operation is abandoned
immediately. If set to ignore, no action is taken and any
further response is ignored; this may result in further
response messages to be queued for that connection, so it
is recommended that long lasting connections are timed out
either by idle-timeout or conn-ttl, so that resources
eventually get released. If set to exop, a cancel
operation (RFC 3909) is issued, resulting in the
cancellation of the current operation; the cancel operation
waits for remote server response, so its use may not be
recommended. If set to exop-discover, support of the
cancel extended operation is detected by reading the remote
server's root DSE.
chase-referrals {YES|no}
enable/disable automatic referral chasing, which is
delegated to the underlying libldap, with rebinding
eventually performed if the rebind-as-user directive is
used. The default is to chase referrals.
conn-pool-max <int>
This directive defines the maximum size of the privileged
connections pool.
conn-ttl <time>
This directive causes a cached connection to be dropped
after a given ttl, regardless of being idle or not. If a
client connection outlives the remote connection, the
client will receive LDAP_UNAVAILABLE when it executes the
next operation.
idassert-authzFrom <authz-regexp>
if defined, selects what local identities are authorized to
exploit the identity assertion feature. The string <authz-
regexp> mostly follows the rules defined for the authzFrom
attribute. See slapd.conf(5), section related to
authz-policy, for details on the syntax of this field.
This parameter differs from the documented behavior in
relation to the meaning of *, which in this case allows
anonymous rather than denies.
idassert-bind bindmethod=none|simple|sasl [binddn=<simple DN>]
[credentials=<simple password>] [saslmech=<SASL mech>]
[secprops=<properties>] [realm=<realm>]
[authcId=<authentication ID>] [authzId=<authorization ID>]
[authz={native|proxyauthz}] [mode=<mode>] [flags=<flags>]
[starttls=no|yes|critical] [tls_cert=<file>]
[tls_key=<file>] [tls_cacert=<file>] [tls_cacertdir=<path>]
[tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_ecname=<names>]
[tls_protocol_min=<version>] [tls_crlcheck=none|peer|all]
Allows one to define the parameters of the authentication
method that is internally used by the proxy to authorize
connections that are authenticated by other databases.
Direct binds are always proxied without any idassert
handling.
The identity defined by this directive, according to the
properties associated to the authentication method, is
supposed to have auth access on the target server to
attributes used on the proxy for authentication and
authorization, and to be allowed to authorize the users.
This requires to have proxyAuthz privileges on a wide set
of DNs, e.g. authzTo=dn.subtree:"", and the remote server
to have authz-policy set to to or both. See slapd.conf(5)
for details on these statements and for remarks and
drawbacks about their usage. The supported bindmethods are
none|simple|sasl
where none is the default, i.e. no identity assertion is
performed.
The authz parameter is used to instruct the SASL bind to
exploit native SASL authorization, if available; since
connections are cached, this should only be used when
authorizing with a fixed identity (e.g. by means of the
authzDN or authzID parameters). Otherwise, the default
proxyauthz is used, i.e. the proxyAuthz control (Proxied
Authorization, RFC 4370) is added to all operations.
The supported modes are:
<mode> := {legacy|anonymous|none|self}
If <mode> is not present, and authzId is given, the proxy
always authorizes that identity. <authorization ID> can be
u:<user>
[dn:]<DN>
The former is supposed to be expanded by the remote server
according to the authz rules; see slapd.conf(5) for
details. In the latter case, whether or not the dn: prefix
is present, the string must pass DN validation and
normalization.
The default mode is legacy, which implies that the proxy
will either perform a simple bind as the authcDN or a SASL
bind as the authcID and assert the client's identity when
it is not anonymous. The other modes imply that the proxy
will always either perform a simple bind as the authcDN or
a SASL bind as the authcID, unless restricted by
idassert-authzFrom rules (see below), in which case the
operation will fail; eventually, it will assert some other
identity according to <mode>. Other identity assertion
modes are anonymous and self, which respectively mean that
the empty or the client's identity will be asserted; none,
which means that no proxyAuthz control will be used, so the
authcDN or the authcID identity will be asserted. For all
modes that require the use of the proxyAuthz control, on
the remote server the proxy identity must have appropriate
authzTo permissions, or the asserted identities must have
appropriate authzFrom permissions. Note, however, that the
ID assertion feature is mostly useful when the asserted
identities do not exist on the remote server.
Flags can be
override,[non-]prescriptive,proxy-authz-[non-]critical,dn-{authzid|whoami}
When the override flag is used, identity assertion takes
place even when the database is authorizing for the
identity of the client, i.e. after binding with the
provided identity, and thus authenticating it, the proxy
performs the identity assertion using the configured
identity and authentication method.
When the prescriptive flag is used (the default),
operations fail with inappropriateAuthentication for those
identities whose assertion is not allowed by the
idassert-authzFrom patterns. If the non-prescriptive flag
is used, operations are performed anonymously for those
identities whose assertion is not allowed by the
idassert-authzFrom patterns.
When the proxy-authz-non-critical flag is used (the
default), the proxyAuthz control is not marked as critical,
in violation of RFC 4370. Use of proxy-authz-critical is
recommended.
When the dn-authzid flag is used, RFC 3829 LDAP
Authorization Identity Controls is used to retrieve the
identity associated to the SASL identity; when the
dn-whoami flag is used, RFC 4532 LDAP Who am I? Operation
is performed after the bind for the same purpose.
The TLS settings default to the same as the main slapd TLS
settings, except for tls_reqcert which defaults to
"demand", and tls_reqsan which defaults to "allow".
The identity associated to this directive is also used for
privileged operations whenever idassert-bind is defined and
acl-bind is not. See acl-bind for details.
idassert-passthru <authz-regexp>
if defined, selects what local identities bypass the
identity assertion feature. Those identities need to be
known by the remote host. The string <authz-regexp>
follows the rules defined for the authzFrom attribute. See
slapd.conf(5), section related to authz-policy, for details
on the syntax of this field.
idle-timeout <time>
This directive causes a cached connection to be dropped
after it has been idle for the specified time. If a client
connection outlives the remote connection, the client will
receive LDAP_UNAVAILABLE when it executes the next
operation.
keepalive <idle>:<probes>:<interval>
The keepalive parameter sets the values of idle, probes,
and interval used to check whether a socket is alive; idle
is the number of seconds a connection needs to remain idle
before TCP starts sending keepalive probes; probes is the
maximum number of keepalive probes TCP should send before
dropping the connection; interval is interval in seconds
between individual keepalive probes. Only some systems
support the customization of these values; the keepalive
parameter is ignored otherwise, and system-wide settings
are used.
tcp-user-timeout <milliseconds>
If non-zero, corresponds to the TCP_USER_TIMEOUT set on the
target connections, overriding the operating system
setting. Only some systems support the customization of
this parameter, it is ignored otherwise and system-wide
settings are used.
network-timeout <time>
Sets the network timeout value after which
poll(2)/select(2) following a connect(2) returns in case of
no activity. The value is in seconds, and it can be
specified as for idle-timeout.
norefs <NO|yes>
If yes, do not return search reference responses. By
default, they are returned unless request is LDAPv2.
omit-unknown-schema <NO|yes>
If yes, do not return objectClasses or attributes that are
not known to the local server. The default is to return
all schema elements.
noundeffilter <NO|yes>
If yes, return success instead of searching if a filter is
undefined or contains undefined portions. By default, the
search is propagated after replacing undefined portions
with (!(objectClass=*)), which corresponds to the empty
result set.
onerr {CONTINUE|stop}
This directive allows one to select the behavior in case an
error is returned by the remote server during a search.
The default, continue, consists in returning success. If
the value is set to stop, the error is returned to the
client.
protocol-version {0,2,3}
This directive indicates what protocol version must be used
to contact the remote server. If set to 0 (the default),
the proxy uses the same protocol version used by the
client, otherwise the requested protocol is used. The
proxy returns unwillingToPerform if an operation that is
incompatible with the requested protocol is attempted.
proxy-whoami {NO|yes}
Turns on proxying of the WhoAmI extended operation. If this
option is given, back-ldap will replace slapd's original
WhoAmI routine with its own. On slapd sessions that were
authenticated by back-ldap, the WhoAmI request will be
forwarded to the remote LDAP server. Other sessions will be
handled by the local slapd, as before. This option is
mainly useful in conjunction with Proxy Authorization.
quarantine <interval>,<num>[;<interval>,<num>[...]]
Turns on quarantine of URIs that returned LDAP_UNAVAILABLE,
so that an attempt to reconnect only occurs at given
intervals instead of any time a client requests an
operation. The pattern is: retry only after at least
interval seconds elapsed since last attempt, for exactly
num times; then use the next pattern. If num for the last
pattern is "+", it retries forever; otherwise, no more
retries occur. The process can be restarted by resetting
the olcDbQuarantine attribute of the database entry in the
configuration backend.
rebind-as-user {NO|yes}
If this option is given, the client's bind credentials are
remembered for rebinds, when trying to re-establish a
broken connection, or when chasing a referral, if
chase-referrals is set to yes. Note, however, that
connection is not re-established automatically after it was
dropped due to idle-timeout or conn-ttl .
session-tracking-request {NO|yes}
Adds session tracking control for all requests. The
client's IP and hostname, and the identity associated to
each request, if known, are sent to the remote server for
informational purposes. This directive is incompatible
with setting protocol-version to 2.
single-conn {NO|yes}
Discards current cached connection when the client rebinds.
t-f-support {NO|yes|discover}
enable if the remote server supports absolute filters (see
RFC 4526 for details). If set to discover, support is
detected by reading the remote server's root DSE.
timeout [<op>=]<val> [...]
This directive allows one to set per-operation timeouts.
Operations can be
<op> ::= bind, add, delete, modrdn, modify, compare, search
The overall duration of the search operation is controlled
either by the timelimit parameter or by server-side
enforced time limits (see timelimit and limits in
slapd.conf(5) for details). This timeout parameter
controls how long the target can be irresponsive before the
operation is aborted. Timeout is meaningless for the
remaining operations, unbind and abandon, which do not
imply any response, while it is not yet implemented in
currently supported extended operations. If no operation
is specified, the timeout val affects all supported
operations.
Note: if the timelimit is exceeded, the operation is
cancelled (according to the cancel directive); the protocol
does not provide any means to rollback operations, so the
client will not be notified about the result of the
operation, which may eventually succeeded or not. In case
the timeout is exceeded during a bind operation, the
connection is destroyed, according to RFC4511.
Note: in some cases, this backend may issue binds prior to
other operations (e.g. to bind anonymously or with some
prescribed identity according to the idassert-bind
directive). In this case, the timeout of the operation
that resulted in the bind is used.
tls {none|[try-]start|[try-]propagate|ldaps} [starttls=no]
[tls_cert=<file>] [tls_key=<file>] [tls_cacert=<file>]
[tls_cacertdir=<path>] [tls_reqcert=never|allow|try|demand]
[tls_reqsan=never|allow|try|demand]
[tls_cipher_suite=<ciphers>] [tls_ecname=<names>]
[tls_crlcheck=none|peer|all]
Specify TLS settings for regular connections.
If the first parameter is not "none" then this configures
the TLS settings to be used for regular connections. The
StartTLS extended operation will be used when establishing
the connection unless the URI directive protocol scheme is
ldaps://. In that case this keyword may only be set to
"ldaps" and the StartTLS operation will not be used.
With propagate, the proxy issues the StartTLS operation
only if the original connection has a TLS layer set up.
The try- prefix instructs the proxy to continue operations
if the StartTLS operation failed; its use is not
recommended.
The TLS settings default to the same as the main slapd TLS
settings, except for tls_reqcert which defaults to
"demand", tls_reqsan which defaults to "allow", and
starttls which is overshadowed by the first keyword and
thus ignored.
use-temporary-conn {NO|yes}
when set to yes, create a temporary connection whenever
competing with other threads for a shared one; otherwise,
wait until the shared connection is available.
The ldap backend does not honor all ACL semantics as described in
slapd.access(5). In general, access checking is delegated to the
remote server(s). Only read (=r) access to the entry pseudo-
attribute and to the other attribute values of the entries
returned by the search operation is honored, which is performed by
the frontend.
The LDAP backend provides basic proxying functionalities to many
overlays. The chain overlay, described in slapo-chain(5), and the
translucent overlay, described in slapo-translucent(5), deserve a
special mention.
Conversely, there are many overlays that are best used in
conjunction with the LDAP backend. The proxycache overlay allows
caching of LDAP search requests (queries) in a local database.
See slapo-pcache(5) for details. The rwm overlay provides DN
rewrite and attribute/objectClass mapping capabilities to the
underlying database. See slapo-rwm(5) for details.
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd-config(5), slapd-meta(5), slapo-chain(5),
slapo-pcache(5), slapo-rwm(5), slapo-translucent(5), slapd(8),
ldap(3).
Howard Chu, with enhancements by Pierangelo Masarati
This page is part of the OpenLDAP (an open source implementation
of the Lightweight Directory Access Protocol) project.
Information about the project can be found at
⟨http://www.openldap.org/⟩. If you have a bug report for this
manual page, see ⟨http://www.openldap.org/its/⟩. This page was
obtained from the project's upstream Git repository
⟨https://git.openldap.org/openldap/openldap.git⟩ on 2025-08-11.
(At that time, the date of the most recent commit that was found
in the repository was 2025-08-05.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
OpenLDAP LDVERSION RELEASEDATE SLAPD-LDAP(5)
Pages that refer to this page: slapd-asyncmeta(5), slapd.backends(5), slapd-meta(5), slapd.overlays(5), slapo-chain(5), slapo-pbind(5), slapo-pcache(5), slapo-rwm(5), slapo-translucent(5)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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