[5357] Shared-networks parser for v4 extended.

src/bin/dhcp4/json_config_parser.cc

@@ -12,8 +12,8 @@
 #include <dhcp/option_definition.h>
 #include <dhcpsrv/cfg_option.h>
 #include <dhcpsrv/cfgmgr.h>
-#include <dhcpsrv/parsers/client_class_def_parser.h>
 #include <dhcp4/json_config_parser.h>
+#include <dhcpsrv/parsers/client_class_def_parser.h>
 #include <dhcpsrv/parsers/dbaccess_parser.h>
 #include <dhcpsrv/parsers/dhcp_parsers.h>
 #include <dhcpsrv/parsers/expiration_config_parser.h>
@@ -22,6 +22,7 @@
 #include <dhcpsrv/parsers/ifaces_config_parser.h>
 #include <dhcpsrv/parsers/option_data_parser.h>
 #include <dhcpsrv/parsers/simple_parser4.h>
+#include <dhcpsrv/parsers/shared_networks_list_parser.h>
 #include <dhcpsrv/timer_mgr.h>
 #include <hooks/hooks_parser.h>
 #include <config/command_mgr.h>
@@ -47,7 +48,12 @@ using namespace isc::hooks;
 
 namespace {
 
-/// @brief Parser that takes care of global DHCPv4 parameters.
+/// @brief Parser that takes care of global DHCPv4 parameters and utility
+///        functions that work on global level.
+///
+/// This class is a collection of utility method that either handle
+/// global parameters (see @ref parse), or conducts operations on
+/// global level (see @ref sanityChecks and @ref copySubnets4).
 ///
 /// See @ref parse method for a list of supported parameters.
 class Dhcp4ConfigParser : public isc::data::SimpleParser {
@@ -82,6 +88,126 @@ public:
         uint16_t dhcp4o6_port = getUint16(global, "dhcp4o6-port");
         cfg->setDhcp4o6Port(dhcp4o6_port);
     }
+
+
+    /// @brief Copies subnets from shared networks to regular subnets container
+    ///
+    /// @param from pointer to shared networks container (copy from here)
+    /// @param dest pointer to cfg subnets4 (copy to here)
+    /// @throw BadValue if any pointer is missing
+    /// @throw DhcpConfigError if there are duplicates (or other subnet defects)
+    void
+    copySubnets4(const CfgSubnets4Ptr dest, const CfgSharedNetworks4Ptr from) {
+
+        if (!dest || !from) {
+            isc_throw(BadValue, "Unable to copy subnets: at least one pointer is null");
+        }
+
+        const SharedNetwork4Collection* networks = from->getAll();
+        if (!networks) {
+            // Nothing to copy. Technically, it should return a pointer to empty
+            // container, but let's handle null pointer as well.
+            return;
+        }
+
+        // Let's go through all the networks one by one
+        for (auto net = networks->begin(); net != networks->end(); ++net) {
+
+            // For each network go through all the subnets in it.
+            const Subnet4Collection* subnets = (*net)->getAllSubnets();
+            if (!subnets) {
+                // Shared network without subnets it weird, but we decided to
+                // accept such configurations.
+                continue;
+            }
+
+            // For each subnet, add it to a list of regular subnets.
+            for (auto subnet = subnets->begin(); subnet != subnets->end(); ++subnet) {
+                dest->add(*subnet);
+            }
+        }
+    }
+
+    /// @brief Conducts global sanity checks
+    ///
+    /// This method is very simply now, but more sanity checks are expected
+    /// in the future.
+    ///
+    /// @param cfg - the parsed structure
+    /// @param global global Dhcp4 scope
+    /// @throw DhcpConfigError in case of issues found
+    void
+    sanityChecks(SrvConfigPtr cfg, ConstElementPtr global) {
+
+        /// Shared network sanity checks
+        const SharedNetwork4Collection* networks = cfg->getCfgSharedNetworks4()->getAll();
+        if (networks) {
+            sharedNetworksSanityChecks(*networks, global->get("shared-networks"));
+        }
+    }
+
+    /// @brief Sanity checks for shared networks
+    ///
+    /// This method verifies if there are no issues with shared networks.
+    /// @param networks pointer to shared networks being checked
+    /// @param json shared-networks element
+    /// @throw DhcpConfigError if issues are encountered
+    void
+    sharedNetworksSanityChecks(const SharedNetwork4Collection& networks,
+                               ConstElementPtr json) {
+
+        // Used for names uniqueness checks.
+        std::set<string> names;
+
+        // Let's go through all the networks one by one
+        for (auto net = networks.begin(); net != networks.end(); ++net) {
+            string txt;
+
+            // Let's check if all subnets have either the same interface
+            // or don't have the interface specified at all.
+            string iface = (*net)->getIface();
+
+            const Subnet4Collection* subnets = (*net)->getAllSubnets();
+            if (subnets) {
+                // For each subnet, add it to a list of regular subnets.
+                for (auto subnet = subnets->begin(); subnet != subnets->end(); ++subnet) {
+                    if (iface.empty()) {
+                        iface = (*subnet)->getIface();
+                        continue;
+                    }
+
+                    if ((*subnet)->getIface().empty()) {
+                        continue;
+                    }
+
+                    if (iface != (*subnet)->getIface()) {
+                        isc_throw(DhcpConfigError, "Subnet " << (*subnet)->toText()
+                                  << " has specified interface " << (*subnet)->getIface()
+                                  << ", but earlier subnet in the same shared-network"
+                                  << " or the shared-network itself used " << iface);
+                    }
+
+                    // Let's collect the subnets in case we later find out the
+                    // subnet doesn't have a mandatory name.
+                    txt += (*subnet)->toText() + " ";
+                }
+            }
+
+            // Next, let's check name of the shared network.
+            if ((*net)->getName().empty()) {
+                isc_throw(DhcpConfigError, "Shared-network with subnets "
+                          << txt << " is missing mandatory 'name' parameter");
+            }
+
+            // Is it unique?
+            if (names.find((*net)->getName()) != names.end()) {
+                isc_throw(DhcpConfigError, "A shared-network with "
+                          "name " << (*net)->getName() << " defined twice.");
+            }
+            names.insert((*net)->getName());
+
+        }
+    }
 };
 
 } // anonymous namespace
@@ -189,6 +315,8 @@ configureDhcp4Server(Dhcpv4Srv&, isc::data::ConstElementPtr config_set,
             parser.parse(cfg_option_def, option_defs);
         }
 
+        Dhcp4ConfigParser global_parser;
+
         // Make parsers grouping.
         const std::map<std::string, ConstElementPtr>& values_map =
                                                         mutable_cfg->mapValue();
@@ -291,11 +419,18 @@ configureDhcp4Server(Dhcpv4Srv&, isc::data::ConstElementPtr config_set,
             }
 
             if (config_pair.first == "shared-networks") {
-                /// @todo We need to create instance of SharedNetworks4ListParser
+
+                /// We need to create instance of SharedNetworks4ListParser
                 /// and parse the list of the shared networks into the
                 /// CfgSharedNetworks4 object. One additional step is then to
                 /// add subnets from the CfgSharedNetworks4 into CfgSubnets4
                 /// as well.
+                SharedNetworks4ListParser parser;
+                CfgSharedNetworks4Ptr cfg = srv_cfg->getCfgSharedNetworks4();
+
+                parser.parse(cfg, config_pair.second);
+
+                global_parser.copySubnets4(srv_cfg->getCfgSubnets4(), cfg);
                 continue;
             }
 
@@ -322,9 +457,13 @@ configureDhcp4Server(Dhcpv4Srv&, isc::data::ConstElementPtr config_set,
         }
 
         // Apply global options in the staging config.
-        Dhcp4ConfigParser global_parser;
         global_parser.parse(srv_cfg, mutable_cfg);
 
+        // This method conducts final sanity checks and tweaks. In particular,
+        // it checks that there is no conflict between plain subnets and those
+        // defined as part of shared networks.
+        global_parser.sanityChecks(srv_cfg, mutable_cfg);
+
     } catch (const isc::Exception& ex) {
         LOG_ERROR(dhcp4_logger, DHCP4_PARSER_FAIL)
                   .arg(config_pair.first).arg(ex.what());

src/bin/dhcp4/tests/config_parser_unittest.cc

@@ -181,6 +181,40 @@ public:
         EXPECT_EQ(expected_code, rcode_);
     }
 
+    /// @brief Convenience method for running configuration
+    ///
+    /// This method does not throw, but signals errors using gtest macros.
+    ///
+    /// @param config text to be parsed as JSON
+    /// @param expected_code expected code (see cc/command_interpreter.h)
+    /// @param exp_error expected text error (check skipped if empty)
+    void configure(std::string config, int expected_code,
+                   std::string exp_error = "") {
+        ConstElementPtr json;
+        ASSERT_NO_THROW(json = parseDHCP4(config, true));
+
+        ConstElementPtr status;
+        EXPECT_NO_THROW(status = configureDhcp4Server(*srv_, json));
+        ASSERT_TRUE(status);
+
+        int rcode;
+        ConstElementPtr comment = parseAnswer(rcode, status);
+        EXPECT_EQ(expected_code, rcode);
+
+        string text;
+        ASSERT_NO_THROW(text = comment->stringValue());
+
+        if (expected_code != rcode) {
+            std::cout << "Reported status: " << text << std::endl;
+        }
+
+        if ((rcode != 0)) {
+            if (!exp_error.empty()) {
+                EXPECT_EQ(exp_error, text);
+            }
+        }
+    }
+
     ~Dhcp4ParserTest() {
         resetConfiguration();
 
@@ -570,6 +604,18 @@ public:
         return (ReturnType());
     }
 
+    void
+    checkSubnet(const Subnet4Collection& col, std::string subnet,
+                uint32_t t1, uint32_t t2, uint32_t valid) {
+        const auto& index = col.get<SubnetPrefixIndexTag>();
+        auto subnet_it = index.find(subnet);
+        ASSERT_NE(subnet_it, index.cend());
+        Subnet4Ptr s = *subnet_it;
+
+        EXPECT_EQ(t1, s->getT1());
+        EXPECT_EQ(t2, s->getT2());
+        EXPECT_EQ(valid, s->getValid());
+    }
 
     /// @brief This utility method attempts to configure using specified
     ///        config and then returns requested pool from requested subnet
@@ -1023,8 +1069,6 @@ TEST_F(Dhcp4ParserTest, reconfigureRemoveSubnet) {
 
     /// CASE 2: Configure 4 subnets, then reconfigure and remove one
     /// from in between (not first, not last)
-
-    /// @todo: Uncomment subnet removal test as part of #3281.
     ASSERT_NO_THROW(json = parseDHCP4(config4));
     EXPECT_NO_THROW(x = configureDhcp4Server(*srv_, json));
     checkResult(x, 0);
@@ -4929,21 +4973,10 @@ TEST_F(Dhcp4ParserTest, invalidPoolRange) {
         " } ] \n"
         "} \n";
 
-    ConstElementPtr json;
-    ASSERT_NO_THROW(json = parseDHCP4(config, true));
-
-    ConstElementPtr status;
-    EXPECT_NO_THROW(status = configureDhcp4Server(*srv_, json));
-    ASSERT_TRUE(status);
-    int rcode;
-    ConstElementPtr comment = parseAnswer(rcode, status);
-    string text;
-    ASSERT_NO_THROW(text = comment->stringValue());
-
-    EXPECT_EQ(1, rcode);
     string expected = "Failed to create pool defined by: "
         "192.0.2.1-19.2.0.200 (<string>:6:26)";
-    EXPECT_EQ(expected, text);
+
+    configure(config, CONTROL_RESULT_ERROR, expected);
 }
 
 // Test verifies the error message for an outside subnet pool range
@@ -4959,23 +4992,269 @@ TEST_F(Dhcp4ParserTest, outsideSubnetPool) {
         " } ] \n"
         "} \n";
 
-    ConstElementPtr json;
-    ASSERT_NO_THROW(json = parseDHCP4(config, true));
-
-    ConstElementPtr status;
-    EXPECT_NO_THROW(status = configureDhcp4Server(*srv_, json));
-    ASSERT_TRUE(status);
-    int rcode;
-    ConstElementPtr comment = parseAnswer(rcode, status);
-    string text;
-    ASSERT_NO_THROW(text = comment->stringValue());
-
-    EXPECT_EQ(1, rcode);
     string expected = "subnet configuration failed: "
         "a pool of type V4, with the following address range: "
         "192.0.2.1-192.0.2.100 does not match the prefix of a subnet: "
         "10.0.2.0/24 to which it is being added (<string>:5:14)";
-    EXPECT_EQ(expected, text);
+
+    configure(config, CONTROL_RESULT_ERROR, expected);
+}
+
+// Test verifies that empty shared networks are accepted.
+TEST_F(Dhcp4ParserTest, sharedNetworksEmpty) {
+    string config = "{\n"
+        "\"valid-lifetime\": 4000, \n"
+        "\"rebind-timer\": 2000, \n"
+        "\"renew-timer\": 1000, \n"
+        "\"subnet4\": [ {  \n"
+        "    \"pools\": [ { \"pool\": \"10.0.2.1 - 10.0.2.100\" } ], \n"
+        "    \"subnet\": \"10.0.2.0/24\"  \n"
+        " } ],\n"
+        "\"shared-networks\": [ ]\n"
+        "} \n";
+
+    configure(config, CONTROL_RESULT_SUCCESS, "");
+}
+
+// Test verifies that if a shared network is defined, it at least has to have
+// a name.
+TEST_F(Dhcp4ParserTest, sharedNetworksNoName) {
+    string config = "{\n"
+        "\"valid-lifetime\": 4000, \n"
+        "\"rebind-timer\": 2000, \n"
+        "\"renew-timer\": 1000, \n"
+        "\"subnet4\": [ {  \n"
+        "    \"pools\": [ { \"pool\": \"10.0.2.1 - 10.0.2.100\" } ], \n"
+        "    \"subnet\": \"10.0.2.0/24\"  \n"
+        " } ],\n"
+        "\"shared-networks\": [ { } ]\n"
+        "} \n";
+
+    EXPECT_THROW(parseDHCP4(config, true), Dhcp4ParseError);
 }
 
+// Test verifies that empty shared networks are accepted.
+TEST_F(Dhcp4ParserTest, sharedNetworksEmptyName) {
+    string config = "{\n"
+        "\"valid-lifetime\": 4000, \n"
+        "\"rebind-timer\": 2000, \n"
+        "\"renew-timer\": 1000, \n"
+        "\"subnet4\": [ {  \n"
+        "    \"pools\": [ { \"pool\": \"10.0.2.1 - 10.0.2.100\" } ], \n"
+        "    \"subnet\": \"10.0.2.0/24\"  \n"
+        " } ],\n"
+        "\"shared-networks\": [ { \"name\": \"\" } ]\n"
+        "} \n";
+
+    configure(config, CONTROL_RESULT_ERROR,
+              "Shared-network with subnets  is missing mandatory 'name' parameter");
+}
+
+// Test verifies that a degenerated shared-network (no subnets) is
+// accepted.
+TEST_F(Dhcp4ParserTest, sharedNetworksName) {
+    string config = "{\n"
+        "\"subnet4\": [ {  \n"
+        "    \"pools\": [ { \"pool\": \"10.0.2.1 - 10.0.2.100\" } ], \n"
+        "    \"subnet\": \"10.0.2.0/24\"  \n"
+        " } ],\n"
+        "\"shared-networks\": [ { \"name\": \"foo\" } ]\n"
+        "} \n";
+
+    configure(config, CONTROL_RESULT_SUCCESS, "");
+
+    // Now verify that the shared network was indeed configured.
+    CfgSharedNetworks4Ptr cfg_net = CfgMgr::instance().getStagingCfg()
+        ->getCfgSharedNetworks4();
+
+    ASSERT_TRUE(cfg_net);
+    const SharedNetwork4Collection* nets = cfg_net->getAll();
+    ASSERT_TRUE(nets);
+    ASSERT_EQ(1, nets->size());
+
+    SharedNetwork4Ptr net = *(nets->begin());
+    ASSERT_TRUE(net);
+
+    EXPECT_EQ("foo", net->getName());
+
+    const Subnet4Collection * subs = net->getAllSubnets();
+    ASSERT_TRUE(subs);
+    EXPECT_EQ(0, subs->size());
+}
+
+// Test verifies that a degenerated shared-network (just one subnet) is
+// accepted.
+TEST_F(Dhcp4ParserTest, sharedNetworks1subnet) {
+    string config = "{\n"
+        "\"valid-lifetime\": 4000, \n"
+        "\"rebind-timer\": 2000, \n"
+        "\"renew-timer\": 1000, \n"
+        "\"shared-networks\": [ {\n"
+        "    \"name\": \"foo\"\n,"
+        "    \"subnet4\": [ { \n"
+        "        \"subnet\": \"192.0.2.0/24\",\n"
+        "        \"pools\": [ { \"pool\": \"192.0.2.1-192.0.2.10\" } ]\n"
+        "    } ]\n"
+        " } ]\n"
+        "} \n";
+
+    configure(config, CONTROL_RESULT_SUCCESS, "");
+
+    // Now verify that the shared network was indeed configured.
+    CfgSharedNetworks4Ptr cfg_net = CfgMgr::instance().getStagingCfg()
+        ->getCfgSharedNetworks4();
+    ASSERT_TRUE(cfg_net);
+
+    // There should be exactly one shared subnet.
+    const SharedNetwork4Collection* nets = cfg_net->getAll();
+    ASSERT_TRUE(nets);
+    ASSERT_EQ(1, nets->size());
+
+    SharedNetwork4Ptr net = *(nets->begin());
+    ASSERT_TRUE(net);
+    EXPECT_EQ("foo", net->getName());
+
+    // It should have one subnet.
+    const Subnet4Collection * subs = net->getAllSubnets();
+    ASSERT_TRUE(subs);
+    EXPECT_EQ(1, subs->size());
+    checkSubnet(*subs, "192.0.2.0/24", 1000, 2000, 4000);
+
+    // Now make sure the subnet was added to global list of subnets.
+    CfgSubnets4Ptr subnets4 = CfgMgr::instance().getStagingCfg()->getCfgSubnets4();
+    ASSERT_TRUE(subnets4);
+
+    subs = subnets4->getAll();
+    ASSERT_TRUE(subs);
+    checkSubnet(*subs, "192.0.2.0/24", 1000, 2000, 4000);
+}
+
+// Test verifies that a a proper shared-network (three subnets) is
+// accepted. It verifies several things:
+// - that more than one subnet can be added to shared subnets
+// - that each subnet being part of the shared subnets is also stored in
+//   global subnets collection
+// - that a subnet can inherit global values
+// - that subnet can override global parameters
+// - that overridden parameters only affect one subnet and not others
+TEST_F(Dhcp4ParserTest, sharedNetworks3subnets) {
+    string config = "{\n"
+        "\"valid-lifetime\": 4000, \n"
+        "\"rebind-timer\": 2000, \n"
+        "\"renew-timer\": 1000, \n"
+        "\"shared-networks\": [ {\n"
+        "    \"name\": \"foo\"\n,"
+        "    \"subnet4\": [\n"
+        "    { \n"
+        "        \"subnet\": \"192.0.1.0/24\",\n"
+        "        \"pools\": [ { \"pool\": \"192.0.1.1-192.0.1.10\" } ]\n"
+        "    },\n"
+        "    { \n"
+        "        \"subnet\": \"192.0.2.0/24\",\n"
+        "        \"pools\": [ { \"pool\": \"192.0.2.1-192.0.2.10\" } ],\n"
+        "        \"renew-timer\": 2,\n"
+        "        \"rebind-timer\": 22,\n"
+        "        \"valid-lifetime\": 222\n"
+        "    },\n"
+        "    { \n"
+        "        \"subnet\": \"192.0.3.0/24\",\n"
+        "        \"pools\": [ { \"pool\": \"192.0.3.1-192.0.3.10\" } ]\n"
+        "    }\n"
+        "    ]\n"
+        " } ]\n"
+        "} \n";
+
+    configure(config, CONTROL_RESULT_SUCCESS, "");
+
+    // Now verify that the shared network was indeed configured.
+    CfgSharedNetworks4Ptr cfg_net = CfgMgr::instance().getStagingCfg()
+        ->getCfgSharedNetworks4();
+
+    // There is expected one shared subnet.
+    ASSERT_TRUE(cfg_net);
+    const SharedNetwork4Collection* nets = cfg_net->getAll();
+    ASSERT_TRUE(nets);
+    ASSERT_EQ(1, nets->size());
+
+    SharedNetwork4Ptr net = *(nets->begin());
+    ASSERT_TRUE(net);
+
+    EXPECT_EQ("foo", net->getName());
+
+    const Subnet4Collection * subs = net->getAllSubnets();
+    ASSERT_TRUE(subs);
+    EXPECT_EQ(3, subs->size());
+    checkSubnet(*subs, "192.0.1.0/24", 1000, 2000, 4000);
+    checkSubnet(*subs, "192.0.2.0/24", 2, 22, 222);
+    checkSubnet(*subs, "192.0.3.0/24", 1000, 2000, 4000);
+
+    // Now make sure the subnet was added to global list of subnets.
+    CfgSubnets4Ptr subnets4 = CfgMgr::instance().getStagingCfg()->getCfgSubnets4();
+    ASSERT_TRUE(subnets4);
+
+    subs = subnets4->getAll();
+    ASSERT_TRUE(subs);
+    checkSubnet(*subs, "192.0.1.0/24", 1000, 2000, 4000);
+    checkSubnet(*subs, "192.0.2.0/24", 2, 22, 222);
+    checkSubnet(*subs, "192.0.3.0/24", 1000, 2000, 4000);
+}
+
+// This test checks if parameters are derived properly:
+// - global to shared network
+// - shared network to subnet
+TEST_F(Dhcp4ParserTest, sharedNetworksDerive) {
+    string config = "{\n"
+        "\"valid-lifetime\": 4, \n"
+        "\"rebind-timer\": 2, \n"
+        "\"renew-timer\": 1, \n"
+        "\"shared-networks\": [ {\n"
+        "    \"name\": \"foo\"\n,"
+        "    \"renew-timer\": 10,\n"
+        "    \"subnet4\": [\n"
+        "    { \n"
+        "        \"subnet\": \"192.0.1.0/24\",\n"
+        "        \"pools\": [ { \"pool\": \"192.0.1.1-192.0.1.10\" } ]\n"
+        "    },\n"
+        "    { \n"
+        "        \"subnet\": \"192.0.2.0/24\",\n"
+        "        \"pools\": [ { \"pool\": \"192.0.2.1-192.0.2.10\" } ],\n"
+        "        \"renew-timer\": 100\n"
+        "    }\n"
+        "    ]\n"
+        " } ]\n"
+        "} \n";
+
+    configure(config, CONTROL_RESULT_SUCCESS, "");
+
+    // Now verify that the shared network was indeed configured.
+    CfgSharedNetworks4Ptr cfg_net = CfgMgr::instance().getStagingCfg()
+        ->getCfgSharedNetworks4();
+
+    // There is expected one shared subnet.
+    ASSERT_TRUE(cfg_net);
+    const SharedNetwork4Collection* nets = cfg_net->getAll();
+    ASSERT_TRUE(nets);
+    ASSERT_EQ(1, nets->size());
+
+    SharedNetwork4Ptr net = *(nets->begin());
+    ASSERT_TRUE(net);
+
+    const Subnet4Collection * subs = net->getAllSubnets();
+    ASSERT_TRUE(subs);
+    EXPECT_EQ(2, subs->size());
+
+    // For the first subnet, the renew-timer should be 10, because it was
+    // derived from shared-network level. Other parameters a derived
+    // from global scope to shared-network level and later again to
+    // subnet4 level.
+    checkSubnet(*subs, "192.0.1.0/24", 10, 2, 4);
+
+    // For the second subnet, the renew-timer should be 100, because it
+    // was specified explicitly. Other parameters a derived
+    // from global scope to shared-network level and later again to
+    // subnet4 level.
+    checkSubnet(*subs, "192.0.2.0/24", 100, 2, 4);
+}
+
+
 }

src/lib/dhcpsrv/parsers/simple_parser4.cc

@@ -133,6 +133,17 @@ size_t SimpleParser4::setAllDefaults(isc::data::ElementPtr global) {
         cnt += setDefaults(mutable_cfg, IFACE4_DEFAULTS);
     }
 
+    // Set defaults for shared networks
+    ConstElementPtr shared = global->get("shared-networks");
+    if (shared) {
+        BOOST_FOREACH(ElementPtr net, shared->listValue()) {
+            ConstElementPtr subs = net->get("subnet4");
+            if (subs) {
+                cnt += setListDefaults(subs, SUBNET4_DEFAULTS);
+            }
+        }
+    }
+
     return (cnt);
 }
 
@@ -148,6 +159,30 @@ size_t SimpleParser4::deriveParameters(isc::data::ElementPtr global) {
         }
     }
 
+    ConstElementPtr shared = global->get("shared-networks");
+    if (shared) {
+        BOOST_FOREACH(ElementPtr net, shared->listValue()) {
+
+            // This level derives global parameters to shared network
+            // level.
+
+            // First try to inherit the parameters from shared network,
+            // if defined there.
+            // Then try to inherit them from global.
+            cnt += SimpleParser::deriveParams(global, net,
+                                              INHERIT_GLOBAL_TO_SUBNET4);
+
+            // Now we need to go thrugh all the subnets in this net.
+            subnets = net->get("subnet4");
+            if (subnets) {
+                BOOST_FOREACH(ElementPtr single_subnet, subnets->listValue()) {
+                    cnt += SimpleParser::deriveParams(net, single_subnet,
+                                                      INHERIT_GLOBAL_TO_SUBNET4);
+                }
+            }
+        }
+    }
+
     return (cnt);
 }