SLAPD-LDAP(5) File Formats Manual SLAPD-LDAP(5)
NAME
slapd-ldap - LDAP backend to slapd
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
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 ses-
sions 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 connec-
tion requires a new thread; as a consequence, the slapd(8) threads pa-
rameter 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.
CONFIGURATION
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 at-
tributes related to entry creation and modification should not be prox-
ied, as they could be mistakenly written to the target server(s), gen-
erating an error. The current implementation automatically sets last-
mod 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 lda-
purl 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 re-
arranged 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 and
recreated after a given ttl, regardless of being idle or not.
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
an recreated after it has been idle for the specified
time.
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.
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.
ACCESS CONTROL
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.
OVERLAYS
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.
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
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).
AUTHOR
Howard Chu, with enhancements by Pierangelo Masarati
OpenLDAP 2.5.13+dfsg-5 2022/07/14 SLAPD-LDAP(5)
Generated by dwww version 1.15 on Mon Sep 1 22:00:53 CEST 2025.