[5357] Addressed comments after review:

- many more parameters are now inherited from shared-network to subnet4
 - parameters now passed as const reference
 - it is no longer possible to specify echo-client-id on shared-network
   level (because it's a global parameter)
 - example config commented properly

src/lib/dhcpsrv/parsers/simple_parser4.cc

@@ -7,6 +7,7 @@
 #include <dhcpsrv/parsers/simple_parser4.h>
 #include <cc/data.h>
 #include <boost/foreach.hpp>
+#include <iostream>
 
 using namespace isc::data;
 
@@ -66,6 +67,12 @@ const SimpleDefaults SimpleParser4::GLOBAL4_DEFAULTS = {
 };
 
 /// @brief This table defines default values for each IPv4 subnet.
+///
+/// Note: When updating this array, please also update SHARED_SUBNET4_DEFAULTS
+/// below. In most cases, those two should be kept in sync, except cases
+/// where a parameter can be derived from shared-networks, but is not
+/// defined on global level. Currently there are two such parameters:
+/// interface and reservation-mode
 const SimpleDefaults SimpleParser4::SUBNET4_DEFAULTS = {
     { "id",               Element::integer, "0" }, // 0 means autogenerate
     { "interface",        Element::string,  "" },
@@ -76,24 +83,51 @@ const SimpleDefaults SimpleParser4::SUBNET4_DEFAULTS = {
     { "4o6-subnet",       Element::string,  "" },
 };
 
+/// @brief This table defines default values for each IPv4 subnet that is
+///        part of a shared network
+///
+/// This is mostly the same as @ref SUBNET4_DEFAULTS, except two parameters
+/// that can be derived from shared-network, but cannot from global scope.
+/// Those are: interface and reservation-mode.
+const SimpleDefaults SimpleParser4::SHARED_SUBNET4_DEFAULTS = {
+    { "id",               Element::integer, "0" }, // 0 means autogenerate
+    { "client-class",     Element::string,  "" },
+    { "4o6-interface",    Element::string,  "" },
+    { "4o6-interface-id", Element::string,  "" },
+    { "4o6-subnet",       Element::string,  "" },
+};
+
+/// @brief This table defines default values for each IPv4 shared network.
+const SimpleDefaults SimpleParser4::SHARED_NETWORK4_DEFAULTS = {
+    { "interface",        Element::string, "" },
+    { "reservation-mode", Element::string, "all" }
+};
+
 /// @brief This table defines default values for interfaces for DHCPv4.
 const SimpleDefaults SimpleParser4::IFACE4_DEFAULTS = {
     { "re-detect", Element::boolean, "true" }
 };
 
-/// @brief List of parameters that can be inherited from the global to subnet4 scope.
+/// @brief List of parameters that can be inherited to subnet4 scope.
 ///
 /// Some parameters may be defined on both global (directly in Dhcp4) and
 /// subnet (Dhcp4/subnet4/...) scope. If not defined in the subnet scope,
 /// the value is being inherited (derived) from the global scope. This
 /// array lists all of such parameters.
-const ParamsList SimpleParser4::INHERIT_GLOBAL_TO_SUBNET4 = {
-    "renew-timer",
-    "rebind-timer",
-    "valid-lifetime",
+///
+/// This list is also used for inheriting from global to shared networks
+/// and from shared networks to subnets within it.
+const ParamsList SimpleParser4::INHERIT_TO_SUBNET4 = {
+    "interface",
     "match-client-id",
-    "next-server"
+    "next-server",
+    "rebind-timer",
+    "relay",
+    "renew-timer",
+    "reservation-mode",
+    "valid-lifetime"
 };
+
 /// @}
 
 /// ---------------------------------------------------------------------------
@@ -137,9 +171,12 @@ size_t SimpleParser4::setAllDefaults(isc::data::ElementPtr global) {
     ConstElementPtr shared = global->get("shared-networks");
     if (shared) {
         BOOST_FOREACH(ElementPtr net, shared->listValue()) {
+
+            cnt += setDefaults(net, SHARED_NETWORK4_DEFAULTS);
+
             ConstElementPtr subs = net->get("subnet4");
             if (subs) {
-                cnt += setListDefaults(subs, SUBNET4_DEFAULTS);
+                cnt += setListDefaults(subs, SHARED_SUBNET4_DEFAULTS);
             }
         }
     }
@@ -155,7 +192,7 @@ size_t SimpleParser4::deriveParameters(isc::data::ElementPtr global) {
     if (subnets) {
         BOOST_FOREACH(ElementPtr single_subnet, subnets->listValue()) {
             cnt += SimpleParser::deriveParams(global, single_subnet,
-                                              INHERIT_GLOBAL_TO_SUBNET4);
+                                              INHERIT_TO_SUBNET4);
         }
     }
 
@@ -169,16 +206,17 @@ size_t SimpleParser4::deriveParameters(isc::data::ElementPtr global) {
             // if defined there.
             // Then try to inherit them from global.
             cnt += SimpleParser::deriveParams(global, net,
-                                              INHERIT_GLOBAL_TO_SUBNET4);
+                                              INHERIT_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);
+                                                      INHERIT_TO_SUBNET4);
                 }
             }
+
         }
     }