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diff --git a/src/common/dns_resolve.h b/src/common/dns_resolve.h
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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2016 SUSE LINUX GmbH
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+#ifndef CEPH_DNS_RESOLVE_H
+#define CEPH_DNS_RESOLVE_H
+
+#include <netinet/in.h>
+#ifndef _WIN32
+#include <resolv.h>
+#endif
+
+#include "common/ceph_mutex.h"
+#include "msg/msg_types.h"		// for entity_addr_t
+
+namespace ceph {
+
+/**
+ * this class is used to facilitate the testing of
+ * resolv.h functions.
+ */
+class ResolvHWrapper {
+  public:
+    virtual ~ResolvHWrapper() {}
+
+#ifdef HAVE_RES_NQUERY
+    virtual int res_nquery(res_state s, const char *hostname, int cls, int type, 
+        u_char *buf, int bufsz);
+
+    virtual int res_nsearch(res_state s, const char *hostname, int cls, int type, 
+        u_char *buf, int bufsz);
+#else
+    virtual int res_query(const char *hostname, int cls, int type,
+        u_char *buf, int bufsz);
+
+    virtual int res_search(const char *hostname, int cls, int type,
+        u_char *buf, int bufsz);
+#endif
+
+};
+
+
+/**
+ * @class DNSResolver
+ *
+ * This is a singleton class that exposes the functionality of DNS querying.
+ */
+class DNSResolver {
+
+  public:
+    // singleton declaration
+    static DNSResolver *get_instance()
+    {
+      static DNSResolver instance;
+      return &instance;
+    }
+    DNSResolver(DNSResolver const&) = delete;
+    void operator=(DNSResolver const&) = delete;
+
+    // this function is used by the unit test
+    static DNSResolver *get_instance(ResolvHWrapper *resolv_wrapper) {
+      DNSResolver *resolv = DNSResolver::get_instance();
+      delete resolv->resolv_h;
+      resolv->resolv_h = resolv_wrapper;
+      return resolv;
+    }
+
+    enum class SRV_Protocol {
+      TCP, UDP
+    };
+
+
+    struct Record {
+      uint16_t priority;
+      uint16_t weight;
+      entity_addr_t addr;
+    };
+
+    int resolve_cname(CephContext *cct, const std::string& hostname,
+        std::string *cname, bool *found);
+
+    /**
+     * Resolves the address given a hostname.
+     *
+     * @param hostname the hostname to resolved
+     * @param[out] addr the hostname's address
+     * @returns 0 on success, negative error code on failure
+     */
+    int resolve_ip_addr(CephContext *cct, const std::string& hostname,
+        entity_addr_t *addr);
+
+    /**
+     * Returns the list of hostnames and addresses that provide a given
+     * service configured as DNS SRV records.
+     *
+     * @param service_name the service name
+     * @param trans_protocol the IP protocol used by the service (TCP or UDP)
+     * @param[out] srv_hosts the hostname to address map of available hosts
+     *             providing the service. If no host exists the map is not
+     *             changed.
+     * @returns 0 on success, negative error code on failure
+     */
+    int resolve_srv_hosts(CephContext *cct, const std::string& service_name,
+        const SRV_Protocol trans_protocol, std::map<std::string, Record> *srv_hosts);
+
+    /**
+     * Returns the list of hostnames and addresses that provide a given
+     * service configured as DNS SRV records.
+     *
+     * @param service_name the service name
+     * @param trans_protocol the IP protocol used by the service (TCP or UDP)
+     * @param domain the domain of the service
+     * @param[out] srv_hosts the hostname to address map of available hosts
+     *             providing the service. If no host exists the map is not
+     *             changed.
+     * @returns 0 on success, negative error code on failure
+     */
+    int resolve_srv_hosts(CephContext *cct, const std::string& service_name,
+        const SRV_Protocol trans_protocol, const std::string& domain,
+        std::map<std::string, Record> *srv_hosts);
+
+  private:
+    DNSResolver() { resolv_h = new ResolvHWrapper(); }
+    ~DNSResolver();
+
+    ceph::mutex lock = ceph::make_mutex("DNSResolver::lock");
+    ResolvHWrapper *resolv_h;
+#ifdef HAVE_RES_NQUERY
+    std::list<res_state> states;
+
+    int get_state(CephContext *cct, res_state *ps);
+    void put_state(res_state s);
+#endif
+
+#ifndef _WIN32
+    /* this private function allows to reuse the res_state structure used
+     * by other function of this class
+     */
+    int resolve_ip_addr(CephContext *cct, res_state *res,
+        const std::string& hostname, entity_addr_t *addr);
+#endif
+
+    std::string srv_protocol_to_str(SRV_Protocol proto) {
+      switch (proto) {
+        case SRV_Protocol::TCP:
+          return "tcp";
+        case SRV_Protocol::UDP:
+          return "udp";
+      }
+      return "";
+    }
+
+};
+
+}
+
+#endif
+