DNS sites support - add AD SRV plugin

https://fedorahosted.org/sssd/ticket/1032

9 files changed, 877 insertions, 5 deletions

diff --git a/src/config/SSSDConfig/__init__.py.in b/src/config/SSSDConfig/__init__.py.in
index f603a2183..256c4b314 100644
--- a/src/config/SSSDConfig/__init__.py.in
+++ b/src/config/SSSDConfig/__init__.py.in
@@ -149,6 +149,7 @@ option_strings = {
     'ad_server' : _('Active Directory server address'),
     'ad_backup_server' : _('Active Directory backup server address'),
     'ad_hostname' : _('Active Directory client hostname'),
+    'ad_enable_dns_sites' : _('Enable DNS sites - location based service discovery'),
 
     # [provider/krb5]
     'krb5_kdcip' : _('Kerberos server address'),
diff --git a/src/config/etc/sssd.api.d/sssd-ad.conf b/src/config/etc/sssd.api.d/sssd-ad.conf
index 4c257173c..b4b1d0ba1 100644
--- a/src/config/etc/sssd.api.d/sssd-ad.conf
+++ b/src/config/etc/sssd.api.d/sssd-ad.conf
@@ -3,6 +3,7 @@ ad_domain = str, None, false
 ad_server = str, None, false
 ad_backup_server = str, None, false
 ad_hostname = str, None, false
+ad_enable_dns_sites = bool, None, false
 ldap_uri = str, None, false
 ldap_backup_uri = str, None, false
 ldap_search_base = str, None, false
diff --git a/src/external/libndr_nbt.m4 b/src/external/libndr_nbt.m4
new file mode 100644
index 000000000..d4d94f2d6
--- /dev/null
+++ b/src/external/libndr_nbt.m4
@@ -0,0 +1,5 @@
+AC_SUBST(NDR_NBT_CFLAGS)
+AC_SUBST(NDR_NBT_LIBS)
+
+PKG_CHECK_MODULES(NDR_NBT, ndr_nbt, ,
+                  AC_MSG_ERROR("Please install Samba 4 development libraries"))
\ No newline at end of file
diff --git a/src/man/sssd-ad.5.xml b/src/man/sssd-ad.5.xml
index 5513c2ee5..95a95f1ac 100644
--- a/src/man/sssd-ad.5.xml
+++ b/src/man/sssd-ad.5.xml
@@ -131,6 +131,27 @@ ldap_id_mapping = False
                     </listitem>
                 </varlistentry>
 
+                <varlistentry>
+                    <term>ad_enable_dns_sites (boolean)</term>
+                    <listitem>
+                        <para>
+                            Enables DNS sites - location based
+                            service discovery.
+                        </para>
+                        <para>
+                            If true and service discovery (see Service
+                            Discovery paragraph at the bottom of the man page)
+                            is enabled, the SSSD will first attempt to discover
+                            the Active Directory server to connect to using the
+                            Active Directory Site Discovery and fall back to
+                            the DNS SRV records if no AD site is found.
+                        </para>
+                        <para>
+                            Default: true
+                        </para>
+                    </listitem>
+                </varlistentry>
+
                 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="include/override_homedir.xml" />
 
                 <varlistentry>
diff --git a/src/providers/ad/ad_common.h b/src/providers/ad/ad_common.h
index 320bf1c9d..7be15ba9b 100644
--- a/src/providers/ad/ad_common.h
+++ b/src/providers/ad/ad_common.h
@@ -37,6 +37,7 @@ enum ad_basic_opt {
     AD_HOSTNAME,
     AD_KEYTAB,
     AD_KRB5_REALM,
+    AD_ENABLE_DNS_SITES,
 
     AD_OPTS_BASIC /* opts counter */
 };
diff --git a/src/providers/ad/ad_init.c b/src/providers/ad/ad_init.c
index 087ec3c45..4d1098689 100644
--- a/src/providers/ad/ad_init.c
+++ b/src/providers/ad/ad_init.c
@@ -35,6 +35,7 @@
 #include "providers/krb5/krb5_auth.h"
 #include "providers/krb5/krb5_init_shared.h"
 #include "providers/ad/ad_id.h"
+#include "providers/ad/ad_srv.h"
 
 struct ad_options *ad_options = NULL;
 
@@ -108,6 +109,8 @@ sssm_ad_id_init(struct be_ctx *bectx,
     struct ad_id_ctx *ad_ctx;
     struct sdap_id_ctx *sdap_ctx;
     const char *hostname;
+    const char *ad_domain;
+    struct ad_srv_plugin_ctx *srv_ctx;
 
     if (!ad_options) {
         ret = common_ad_init(bectx);
@@ -178,11 +181,28 @@ sssm_ad_id_init(struct be_ctx *bectx,
 
     /* setup SRV lookup plugin */
     hostname = dp_opt_get_string(ad_options->basic, AD_HOSTNAME);
-    ret = be_fo_set_dns_srv_lookup_plugin(bectx, hostname);
-    if (ret != EOK) {
-        DEBUG(SSSDBG_CRIT_FAILURE, ("Unable to set SRV lookup plugin "
-                                    "[%d]: %s\n", ret, strerror(ret)));
-        goto done;
+    if (dp_opt_get_bool(ad_options->basic, AD_ENABLE_DNS_SITES)) {
+        /* use AD plugin */
+        ad_domain = dp_opt_get_string(ad_options->basic, AD_DOMAIN);
+        srv_ctx = ad_srv_plugin_ctx_init(bectx, bectx->be_res,
+                                         default_host_dbs, ad_options->id,
+                                         hostname, ad_domain);
+        if (srv_ctx == NULL) {
+            DEBUG(SSSDBG_FATAL_FAILURE, ("Out of memory?\n"));
+            ret = ENOMEM;
+            goto done;
+        }
+
+        be_fo_set_srv_lookup_plugin(bectx, ad_srv_plugin_send,
+                                    ad_srv_plugin_recv, srv_ctx, "AD");
+    } else {
+        /* fall back to standard plugin */
+        ret = be_fo_set_dns_srv_lookup_plugin(bectx, hostname);
+        if (ret != EOK) {
+            DEBUG(SSSDBG_CRIT_FAILURE, ("Unable to set SRV lookup plugin "
+                                        "[%d]: %s\n", ret, strerror(ret)));
+            goto done;
+        }
     }
 
     *ops = &ad_id_ops;
diff --git a/src/providers/ad/ad_opts.h b/src/providers/ad/ad_opts.h
index 4b87e0c04..c48be8674 100644
--- a/src/providers/ad/ad_opts.h
+++ b/src/providers/ad/ad_opts.h
@@ -34,6 +34,7 @@ struct dp_option ad_basic_opts[] = {
     { "ad_hostname", DP_OPT_STRING, NULL_STRING, NULL_STRING },
     { "krb5_keytab", DP_OPT_STRING, NULL_STRING, NULL_STRING },
     { "krb5_realm", DP_OPT_STRING, NULL_STRING, NULL_STRING},
+    { "ad_enable_dns_sites", DP_OPT_BOOL, BOOL_TRUE, BOOL_TRUE },
     DP_OPTION_TERMINATOR
 };
 
diff --git a/src/providers/ad/ad_srv.c b/src/providers/ad/ad_srv.c
new file mode 100644
index 000000000..5dd06f623
--- /dev/null
+++ b/src/providers/ad/ad_srv.c
@@ -0,0 +1,773 @@
+/*
+    Authors:
+        Pavel B??ezina <pbrezina@redhat.com>
+
+    Copyright (C) 2013 Red Hat
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <string.h>
+#include <talloc.h>
+#include <tevent.h>
+#include <ndr.h>
+#include <ndr/ndr_nbt.h>
+
+#include "util/util.h"
+#include "util/sss_ldap.h"
+#include "resolv/async_resolv.h"
+#include "providers/dp_backend.h"
+#include "providers/fail_over.h"
+#include "providers/fail_over_srv.h"
+#include "providers/ldap/sdap.h"
+#include "providers/ldap/sdap_async.h"
+
+#define AD_SITE_DOMAIN "%s._sites.%s"
+#define AD_AT_DNS_DOMAIN "DnsDomain"
+#define AD_AT_NT_VERSION "NtVer"
+#define AD_AT_NETLOGON "netlogon"
+
+struct ad_get_dc_servers_state {
+    struct fo_server_info *servers;
+    size_t num_servers;
+};
+
+static void ad_get_dc_servers_done(struct tevent_req *subreq);
+
+static struct tevent_req *ad_get_dc_servers_send(TALLOC_CTX *mem_ctx,
+                                                 struct tevent_context *ev,
+                                                 struct resolv_ctx *resolv_ctx,
+                                                 const char *domain)
+{
+    struct ad_get_dc_servers_state *state = NULL;
+    struct tevent_req *req = NULL;
+    struct tevent_req *subreq = NULL;
+    const char **domains = NULL;
+    errno_t ret;
+
+    req = tevent_req_create(mem_ctx, &state,
+                            struct ad_get_dc_servers_state);
+    if (req == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("tevent_req_create() failed\n"));
+        return NULL;
+    }
+
+    domains = talloc_zero_array(state, const char *, 2);
+    if (domains == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    domains[0] = talloc_strdup(domains, domain);
+    if (domains[0] == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("Looking up domain controllers in domain %s\n",
+                              domain));
+
+    subreq = fo_discover_srv_send(state, ev, resolv_ctx,
+                                  "ldap", FO_PROTO_TCP, domains);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    tevent_req_set_callback(subreq, ad_get_dc_servers_done, req);
+
+    return req;
+
+immediately:
+    tevent_req_error(req, ret);
+    tevent_req_post(req, ev);
+
+    return req;
+}
+
+static void ad_get_dc_servers_done(struct tevent_req *subreq)
+{
+    struct ad_get_dc_servers_state *state = NULL;
+    struct tevent_req *req = NULL;
+    char *domain = NULL;
+    errno_t ret;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_get_dc_servers_state);
+
+    ret = fo_discover_srv_recv(state, subreq, &domain,
+                               &state->servers, &state->num_servers);
+    talloc_zfree(subreq);
+    if (ret != EOK) {
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("Found %lu domain controllers in domain %s\n",
+                              state->num_servers, domain));
+
+done:
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+        return;
+    }
+
+    tevent_req_done(req);
+}
+
+static int ad_get_dc_servers_recv(TALLOC_CTX *mem_ctx,
+                                  struct tevent_req *req,
+                                  struct fo_server_info **_dcs,
+                                  size_t *_num_dcs)
+{
+    struct ad_get_dc_servers_state *state = NULL;
+    state = tevent_req_data(req, struct ad_get_dc_servers_state);
+
+    TEVENT_REQ_RETURN_ON_ERROR(req);
+
+    *_dcs = talloc_steal(mem_ctx, state->servers);
+    *_num_dcs = state->num_servers;
+
+    return EOK;
+}
+
+struct ad_get_client_site_state {
+    struct tevent_context *ev;
+    struct be_resolv_ctx *be_res;
+    enum host_database *host_db;
+    struct sdap_options *opts;
+    const char *ad_domain;
+    struct fo_server_info *dcs;
+    size_t num_dcs;
+    size_t dc_index;
+    struct fo_server_info dc;
+
+    struct sdap_handle *sh;
+    char *site;
+};
+
+static errno_t ad_get_client_site_next_dc(struct tevent_req *req);
+static void ad_get_client_site_connect_done(struct tevent_req *subreq);
+static void ad_get_client_site_done(struct tevent_req *subreq);
+
+struct tevent_req *ad_get_client_site_send(TALLOC_CTX *mem_ctx,
+                                           struct tevent_context *ev,
+                                           struct be_resolv_ctx *be_res,
+                                           enum host_database *host_db,
+                                           struct sdap_options *opts,
+                                           const char *ad_domain,
+                                           struct fo_server_info *dcs,
+                                           size_t num_dcs)
+{
+    struct ad_get_client_site_state *state = NULL;
+    struct tevent_req *req = NULL;
+    errno_t ret;
+
+    req = tevent_req_create(mem_ctx, &state,
+                            struct ad_get_client_site_state);
+    if (req == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("tevent_req_create() failed\n"));
+        return NULL;
+    }
+
+    if (be_res == NULL || host_db == NULL || opts == NULL) {
+        ret = EINVAL;
+        goto immediately;
+    }
+
+    state->ev = ev;
+    state->be_res = be_res;
+    state->host_db = host_db;
+    state->opts = opts;
+    state->ad_domain = ad_domain;
+    state->dcs = dcs;
+    state->num_dcs = num_dcs;
+
+    state->dc_index = 0;
+    ret = ad_get_client_site_next_dc(req);
+    if (ret == EOK) {
+        ret = ENOENT;
+        goto immediately;
+    } else if (ret != EAGAIN) {
+        goto immediately;
+    }
+
+    return req;
+
+immediately:
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else {
+        tevent_req_error(req, ret);
+    }
+    tevent_req_post(req, ev);
+
+    return req;
+}
+
+static errno_t ad_get_client_site_next_dc(struct tevent_req *req)
+{
+    struct ad_get_client_site_state *state = NULL;
+    struct tevent_req *subreq = NULL;
+    errno_t ret;
+
+    state = tevent_req_data(req, struct ad_get_client_site_state);
+
+    if (state->dc_index >= state->num_dcs) {
+        ret = EOK;
+        goto done;
+    }
+
+    state->dc = state->dcs[state->dc_index];
+
+    subreq = sdap_connect_host_send(state, state->ev, state->opts,
+                                    state->be_res->resolv,
+                                    state->be_res->family_order,
+                                    state->host_db, "ldap", state->dc.host,
+                                    state->dc.port, false);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    tevent_req_set_callback(subreq, ad_get_client_site_connect_done, req);
+
+    state->dc_index++;
+    ret = EAGAIN;
+
+done:
+    return ret;
+}
+
+static void ad_get_client_site_connect_done(struct tevent_req *subreq)
+{
+    struct ad_get_client_site_state *state = NULL;
+    struct tevent_req *req = NULL;
+    static const char *attrs[] = {AD_AT_NETLOGON, NULL};
+    char *filter = NULL;
+    char *ntver = NULL;
+    errno_t ret;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_get_client_site_state);
+
+    ret = sdap_connect_host_recv(state, subreq, &state->sh);
+    talloc_zfree(subreq);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_MINOR_FAILURE, ("Unable to connect to domain controller "
+              "[%s:%d]\n", state->dc.host, state->dc.port));
+
+        ret = ad_get_client_site_next_dc(req);
+        if (ret == EOK) {
+            ret = ENOENT;
+        }
+
+        goto done;
+    }
+
+    ntver = sss_ldap_encode_ndr_uint32(state, NETLOGON_NT_VERSION_5EX |
+                                       NETLOGON_NT_VERSION_WITH_CLOSEST_SITE);
+    if (ntver == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    filter = talloc_asprintf(state, "(&(%s=%s)(%s=%s))",
+                             AD_AT_DNS_DOMAIN, state->ad_domain,
+                             AD_AT_NT_VERSION, ntver);
+    if (filter == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    subreq = sdap_get_generic_send(state, state->ev, state->opts, state->sh,
+                                   "", LDAP_SCOPE_BASE, filter,
+                                   attrs, NULL, 0,
+                                   dp_opt_get_int(state->opts->basic,
+                                                  SDAP_SEARCH_TIMEOUT),
+                                   false);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    tevent_req_set_callback(subreq, ad_get_client_site_done, req);
+
+    ret = EAGAIN;
+
+done:
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+
+    return;
+}
+
+static errno_t ad_get_client_site_parse_ndr(TALLOC_CTX *mem_ctx,
+                                            uint8_t *data,
+                                            size_t length,
+                                            char **_site_name)
+{
+    TALLOC_CTX *tmp_ctx = NULL;
+    struct ndr_pull *ndr_pull = NULL;
+    struct netlogon_samlogon_response response;
+    enum ndr_err_code ndr_err;
+    char *site = NULL;
+    DATA_BLOB blob;
+    errno_t ret;
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("talloc_new() failed\n"));
+        return ENOMEM;
+    }
+
+    blob.data = data;
+    blob.length = length;
+
+    ndr_pull = ndr_pull_init_blob(&blob, mem_ctx);
+    if (ndr_pull == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, ("ndr_pull_init_blob() failed.\n"));
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ndr_err = ndr_pull_netlogon_samlogon_response(ndr_pull, NDR_SCALARS,
+                                                  &response);
+    if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
+        DEBUG(SSSDBG_OP_FAILURE, ("ndr_pull_netlogon_samlogon_response() "
+                                  "failed [%d]\n", ndr_err));
+        ret = EBADMSG;
+        goto done;
+    }
+
+    if (!(response.ntver & NETLOGON_NT_VERSION_5EX)) {
+        DEBUG(SSSDBG_OP_FAILURE, ("This NT version does not provide site "
+                                  "information [%x]\n", response.ntver));
+        ret = EBADMSG;
+        goto done;
+    }
+
+    if (response.data.nt5_ex.client_site != NULL) {
+        site = talloc_strdup(tmp_ctx, response.data.nt5_ex.client_site);
+    } else if (response.data.nt5_ex.next_closest_site != NULL) {
+        site = talloc_strdup(tmp_ctx, response.data.nt5_ex.next_closest_site);
+    } else {
+        ret = ENOENT;
+        goto done;
+    }
+
+    if (site == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    *_site_name = talloc_steal(mem_ctx, site);
+
+    ret = EOK;
+
+done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+static void ad_get_client_site_done(struct tevent_req *subreq)
+{
+    struct ad_get_client_site_state *state = NULL;
+    struct tevent_req *req = NULL;
+    struct ldb_message_element *el = NULL;
+    struct sysdb_attrs **reply = NULL;
+    size_t reply_count;
+    errno_t ret;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_get_client_site_state);
+
+    ret = sdap_get_generic_recv(subreq, state, &reply_count, &reply);
+    talloc_zfree(subreq);
+
+    /* we're done with this LDAP, close connection */
+    talloc_zfree(state->sh);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, ("Unable to get netlogon information\n"));
+
+        ret = ad_get_client_site_next_dc(req);
+        if (ret == EOK) {
+            ret = ENOENT;
+        }
+        goto done;
+    }
+
+    if (reply_count == 0) {
+        DEBUG(SSSDBG_OP_FAILURE, ("No netlogon information retrieved\n"));
+        ret = ENOENT;
+        goto done;
+    }
+
+    ret = sysdb_attrs_get_el(reply[0], AD_AT_NETLOGON, &el);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, ("sysdb_attrs_get_el() failed\n"));
+        goto done;
+    }
+
+    if (el->num_values == 0) {
+        DEBUG(SSSDBG_OP_FAILURE, ("netlogon has no value\n"));
+        ret = ENOENT;
+        goto done;
+    } else if (el->num_values > 1) {
+        DEBUG(SSSDBG_OP_FAILURE, ("More than one netlogon value?\n"));
+        ret = EIO;
+        goto done;
+    }
+
+    ret = ad_get_client_site_parse_ndr(state, el->values[0].data,
+                                       el->values[0].length, &state->site);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, ("Unable to retrieve site name [%d]: %s\n",
+                                  ret, strerror(ret)));
+        ret = ENOENT;
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("Found site: %s\n", state->site));
+
+done:
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+        return;
+    }
+
+    tevent_req_done(req);
+}
+
+int ad_get_client_site_recv(TALLOC_CTX *mem_ctx,
+                            struct tevent_req *req,
+                            char **_site)
+{
+    struct ad_get_client_site_state *state = NULL;
+    state = tevent_req_data(req, struct ad_get_client_site_state);
+
+    TEVENT_REQ_RETURN_ON_ERROR(req);
+
+    *_site = talloc_steal(mem_ctx, state->site);
+
+    return EOK;
+}
+
+struct ad_srv_plugin_ctx {
+    struct be_resolv_ctx *be_res;
+    enum host_database *host_dbs;
+    struct sdap_options *opts;
+    const char *hostname;
+    const char *ad_domain;
+};
+
+struct ad_srv_plugin_ctx *
+ad_srv_plugin_ctx_init(TALLOC_CTX *mem_ctx,
+                       struct be_resolv_ctx *be_res,
+                       enum host_database *host_dbs,
+                       struct sdap_options *opts,
+                       const char *hostname,
+                       const char *ad_domain)
+{
+    struct ad_srv_plugin_ctx *ctx = NULL;
+
+    ctx = talloc_zero(mem_ctx, struct ad_srv_plugin_ctx);
+    if (ctx == NULL) {
+        return NULL;
+    }
+
+    ctx->be_res = be_res;
+    ctx->host_dbs = host_dbs;
+    ctx->opts = opts;
+
+    ctx->hostname = talloc_strdup(ctx, hostname);
+    if (ctx->hostname == NULL) {
+        goto fail;
+    }
+
+    ctx->ad_domain = talloc_strdup(ctx, ad_domain);
+    if (ctx->ad_domain == NULL) {
+        goto fail;
+    }
+
+    return ctx;
+
+fail:
+    talloc_free(ctx);
+    return NULL;
+}
+
+struct ad_srv_plugin_state {
+    struct tevent_context *ev;
+    struct ad_srv_plugin_ctx *ctx;
+    const char *service;
+    const char *protocol;
+    const char *discovery_domain;
+
+    char *site;
+    char *dns_domain;
+    struct fo_server_info *primary_servers;
+    size_t num_primary_servers;
+    struct fo_server_info *backup_servers;
+    size_t num_backup_servers;
+};
+
+static void ad_srv_plugin_dcs_done(struct tevent_req *subreq);
+static void ad_srv_plugin_site_done(struct tevent_req *subreq);
+static void ad_srv_plugin_servers_done(struct tevent_req *subreq);
+
+/* 1. Do a DNS lookup to find any DC in domain
+ *    _ldap._tcp.domain.name
+ * 2. Send a CLDAP ping to the found DC to get the desirable site
+ * 3. Do a DNS lookup to find SRV in the site (a)
+ *    _service._protocol.site-name._sites.domain.name
+ * 4. Do a DNS lookup to find global SRV records (b)
+ *    _service._protocol.domain.name
+ * 5. If the site is found, use (a) as primary and (b) as backup servers,
+ *    otherwise use (b) as primary servers
+ */
+struct tevent_req *ad_srv_plugin_send(TALLOC_CTX *mem_ctx,
+                                       struct tevent_context *ev,
+                                       const char *service,
+                                       const char *protocol,
+                                       const char *discovery_domain,
+                                       void *pvt)
+{
+    struct ad_srv_plugin_state *state = NULL;
+    struct ad_srv_plugin_ctx *ctx = NULL;
+    struct tevent_req *req = NULL;
+    struct tevent_req *subreq = NULL;
+    errno_t ret;
+
+    req = tevent_req_create(mem_ctx, &state,
+                            struct ad_srv_plugin_state);
+    if (req == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, ("tevent_req_create() failed\n"));
+        return NULL;
+    }
+
+    ctx = talloc_get_type(pvt, struct ad_srv_plugin_ctx);
+    if (ctx == NULL) {
+        ret = EINVAL;
+        goto immediately;
+    }
+
+    state->ev = ev;
+    state->ctx = ctx;
+
+    state->service = talloc_strdup(state, service);
+    if (state->service == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    state->protocol = talloc_strdup(state, protocol);
+    if (state->protocol == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    if (discovery_domain != NULL) {
+        state->discovery_domain = talloc_strdup(state, discovery_domain);
+    } else {
+        state->discovery_domain = talloc_strdup(state, ctx->ad_domain);
+    }
+    if (state->discovery_domain == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("About to find domain controllers\n"));
+
+    subreq = ad_get_dc_servers_send(state, ev, ctx->be_res->resolv,
+                                    state->discovery_domain);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    tevent_req_set_callback(subreq, ad_srv_plugin_dcs_done, req);
+
+    return req;
+
+immediately:
+    tevent_req_error(req, ret);
+    tevent_req_post(req, ev);
+
+    return req;
+}
+
+static void ad_srv_plugin_dcs_done(struct tevent_req *subreq)
+{
+    struct ad_srv_plugin_state *state = NULL;
+    struct tevent_req *req = NULL;
+    struct fo_server_info *dcs = NULL;
+    size_t num_dcs = 0;
+    errno_t ret;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_srv_plugin_state);
+
+    ret = ad_get_dc_servers_recv(state, subreq, &dcs, &num_dcs);
+    talloc_zfree(subreq);
+    if (ret != EOK) {
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("About to locate suitable site\n"));
+
+    subreq = ad_get_client_site_send(state, state->ev,
+                                     state->ctx->be_res,
+                                     state->ctx->host_dbs,
+                                     state->ctx->opts,
+                                     state->ctx->ad_domain,
+                                     dcs, num_dcs);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    tevent_req_set_callback(subreq, ad_srv_plugin_site_done, req);
+
+    ret = EAGAIN;
+
+done:
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+
+    return;
+}
+
+static void ad_srv_plugin_site_done(struct tevent_req *subreq)
+{
+    struct ad_srv_plugin_state *state = NULL;
+    struct tevent_req *req = NULL;
+    const char *primary_domain = NULL;
+    const char *backup_domain = NULL;
+    errno_t ret;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_srv_plugin_state);
+
+    ret = ad_get_client_site_recv(state, subreq, &state->site);
+    talloc_zfree(subreq);
+    if (ret == EOK) {
+        primary_domain = talloc_asprintf(state, AD_SITE_DOMAIN,
+                                         state->site, state->discovery_domain);
+        if (primary_domain == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+
+        backup_domain = state->discovery_domain;
+    } else if (ret == ENOENT) {
+        primary_domain = state->discovery_domain;
+        backup_domain = NULL;
+    } else {
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("About to discover primary and "
+                              "backup servers\n"));
+
+    subreq = fo_discover_servers_send(state, state->ev,
+                                      state->ctx->be_res->resolv,
+                                      state->service, state->protocol,
+                                      primary_domain, backup_domain);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    tevent_req_set_callback(subreq, ad_srv_plugin_servers_done, req);
+
+    ret = EAGAIN;
+
+done:
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+
+    return;
+}
+
+static void ad_srv_plugin_servers_done(struct tevent_req *subreq)
+{
+    struct ad_srv_plugin_state *state = NULL;
+    struct tevent_req *req = NULL;
+    errno_t ret;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_srv_plugin_state);
+
+    ret = fo_discover_servers_recv(state, subreq, &state->dns_domain,
+                                   &state->primary_servers,
+                                   &state->num_primary_servers,
+                                   &state->backup_servers,
+                                   &state->num_backup_servers);
+    talloc_zfree(subreq);
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+        return;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, ("Got %lu primary and %lu backup servers\n",
+          state->num_primary_servers, state->num_backup_servers));
+
+    tevent_req_done(req);
+}
+
+errno_t ad_srv_plugin_recv(TALLOC_CTX *mem_ctx,
+                           struct tevent_req *req,
+                           char **_dns_domain,
+                           struct fo_server_info **_primary_servers,
+                           size_t *_num_primary_servers,
+                           struct fo_server_info **_backup_servers,
+                           size_t *_num_backup_servers)
+{
+    struct ad_srv_plugin_state *state = NULL;
+    state = tevent_req_data(req, struct ad_srv_plugin_state);
+
+    TEVENT_REQ_RETURN_ON_ERROR(req);
+
+    if (_primary_servers) {
+        *_primary_servers = talloc_steal(mem_ctx, state->primary_servers);
+    }
+
+    if (_num_primary_servers) {
+        *_num_primary_servers = state->num_primary_servers;
+    }
+
+    if (_backup_servers) {
+        *_backup_servers = talloc_steal(mem_ctx, state->backup_servers);
+    }
+
+    if (_num_backup_servers) {
+        *_num_backup_servers = state->num_backup_servers;
+    }
+
+    if (_dns_domain) {
+        *_dns_domain = talloc_steal(mem_ctx, state->dns_domain);
+    }
+
+
+    return EOK;
+}
diff --git a/src/providers/ad/ad_srv.h b/src/providers/ad/ad_srv.h
new file mode 100644
index 000000000..adf29b07a
--- /dev/null
+++ b/src/providers/ad/ad_srv.h
@@ -0,0 +1,49 @@
+/*
+    Authors:
+        Pavel B??ezina <pbrezina@redhat.com>
+
+    Copyright (C) 2013 Red Hat
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __AD_SRV_H__
+#define __AD_SRV_H__
+
+struct ad_srv_plugin_ctx;
+
+struct ad_srv_plugin_ctx *
+ad_srv_plugin_ctx_init(TALLOC_CTX *mem_ctx,
+                       struct be_resolv_ctx *be_res,
+                       enum host_database *host_dbs,
+                       struct sdap_options *opts,
+                       const char *hostname,
+                       const char *ad_domain);
+
+struct tevent_req *ad_srv_plugin_send(TALLOC_CTX *mem_ctx,
+                                       struct tevent_context *ev,
+                                       const char *service,
+                                       const char *protocol,
+                                       const char *discovery_domain,
+                                       void *pvt);
+
+errno_t ad_srv_plugin_recv(TALLOC_CTX *mem_ctx,
+                            struct tevent_req *req,
+                            char **_dns_domain,
+                            struct fo_server_info **_primary_servers,
+                            size_t *_num_primary_servers,
+                            struct fo_server_info **_backup_servers,
+                            size_t *_num_backup_servers);
+
+#endif /* __AD_SRV_H__ */