[dhcp_server] Support scenario that gatway is not configured (sonic-net#21462)

Why I did it
DHCP default route shoule be an optional config to DHCP client

Work item tracking
Microsoft ADO (number only): 30877295

How I did it
Support to do not send default route to dhcp client

How to verify it
UT
Install new image to test

Author: yaqiangz

dockers/docker-dhcp-server/kea-dhcp4.conf.j2

@@ -63,10 +63,12 @@
                         "always-send": {{ config["always_send"] }}
                     },
     {%- endfor %}
+    {%- if "gateway" in subnet_info -%}
                     {
                         "name": "routers",
-                        "data": "{{ subnet_info["gateway"] if "gateway" in subnet_info else subnet_info["server_id"] }}"
+                        "data": "{{ subnet_info["gateway"] }}"
                     },
+    {%- endif -%}
                     {
                         "name": "dhcp-server-identifier",
                         "data": "{{ subnet_info["server_id"] }}"

src/sonic-dhcp-utilities/dhcp_utilities/dhcpservd/dhcp_cfggen.py

@@ -229,11 +229,12 @@ def _construct_obj_for_template(self, dhcp_server_ipv4, port_ips, hostname, cust
                         "id": MID_PLANE_BRIDGE_SUBNET_ID if smart_switch else dhcp_interface_name.replace("Vlan", ""),
                         "subnet": str(ipaddress.ip_network(dhcp_interface_ip, strict=False)),
                         "pools": pools,
-                        "gateway": dhcp_config["gateway"],
                         "server_id": dhcp_interface_ip.split("/")[0],
                         "lease_time": dhcp_config["lease_time"] if "lease_time" in dhcp_config else DEFAULT_LEASE_TIME,
                         "customized_options": curr_options
                     }
+                    if "gateway" in dhcp_config:
+                        subnet_obj["gateway"] = dhcp_config["gateway"]
                     subnets.append(subnet_obj)
         render_obj = {
             "subnets": subnets,

src/sonic-dhcp-utilities/tests/test_data/kea-dhcp4.conf.j2

@@ -63,10 +63,12 @@
                         "always-send": {{ config["always_send"] }}
                     },
     {%- endfor %}
+    {%- if "gateway" in subnet_info %}
                     {
                         "name": "routers",
-                        "data": "{{ subnet_info["gateway"] if "gateway" in subnet_info else subnet_info["server_id"] }}"
+                        "data": "{{ subnet_info["gateway"] }}"
                     },
+    {%- endif %}
                     {
                         "name": "dhcp-server-identifier",
                         "data": "{{ subnet_info["server_id"] }}"

src/sonic-dhcp-utilities/tests/test_data/mock_config_db.json

@@ -83,7 +83,6 @@
                 "option60",
                 "option223"
             ],
-            "gateway": "192.168.3.1",
             "lease_time": "900",
             "mode": "PORT",
             "netmask": "255.255.255.0",

src/sonic-dhcp-utilities/tests/test_dhcp_cfggen.py

@@ -70,6 +70,24 @@
                 ],
                 "valid-lifetime": 900,
                 "reservations": []
+            },
+            {
+                "id": 4000,
+                "subnet": "192.168.3.0/24",
+                "pools": [
+                    {
+                        "pool": "192.168.3.2 - 192.168.3.3",
+                        "client-class": "sonic-host:etp11"
+                    }
+                ],
+                "option-data": [
+                    {
+                        "name": "dhcp-server-identifier",
+                        "data": "192.168.3.1"
+                    }
+                ],
+                "valid-lifetime": 900,
+                "reservations": []
             }
         ],
         "loggers": [
@@ -93,12 +111,23 @@
             {
                 "name": "sonic-host:etp7",
                 "test": "substring(relay4[1].hex, -15, 15) == 'sonic-host:etp7'"
+            },
+            {
+                "name": "sonic-host:etp11",
+                "test": "substring(relay4[1].hex, -16, 16) == 'sonic-host:etp11'"
             }
         ]
     }
 }
 expected_dhcp_config_without_port_config = {
     "Dhcp4": {
+        "option-def": [
+            {
+                "name": "option223",
+                "code": 223,
+                "type": "string"
+            }
+        ],
         "hooks-libraries": [
             {
                 "library": "/usr/local/lib/kea/hooks/libdhcp_run_script.so",
@@ -194,11 +223,23 @@
                     "value": "dummy_value"
                 }
             }
+        },
+        {
+            "subnet": "192.168.3.0/24", 'id': '4000',
+            "pools": [{"range": "192.168.3.2 - 192.168.3.3", "client_class": "sonic-host:etp11"}],
+            "server_id": "192.168.3.1", "lease_time": "900",
+            "customized_options": {
+                "option223": {
+                    "always_send": "true",
+                    "value": "dummy_value"
+                }
+            }
         }
     ],
     "client_classes": [
         {"name": "sonic-host:etp8", "condition": "substring(relay4[1].hex, -15, 15) == 'sonic-host:etp8'"},
-        {"name": "sonic-host:etp7", "condition": "substring(relay4[1].hex, -15, 15) == 'sonic-host:etp7'"}
+        {"name": "sonic-host:etp7", "condition": "substring(relay4[1].hex, -15, 15) == 'sonic-host:etp7'"},
+        {"name": "sonic-host:etp11", "condition": "substring(relay4[1].hex, -16, 16) == 'sonic-host:etp11'"}
     ],
     "lease_update_script_path": "/etc/kea/lease_update.sh",
     "lease_path": "/tmp/kea-lease.csv",
@@ -238,9 +279,9 @@
             "id": "218",
             "type": "string",
             "value": "long_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_value" +
-                        "long_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_value" +
-                        "long_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_value" +
-                        "long_valuelong_valuelong_valuelong_valuelong_value"
+                     "long_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_value" +
+                     "long_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_valuelong_value" +
+                     "long_valuelong_valuelong_valuelong_valuelong_value"
         },
         "option217": {
             "id": "217",
@@ -359,6 +400,11 @@ def test_construct_obj_for_template(mock_swsscommon_dbconnector_init, mock_parse
                 "etp9": []
             }
         },
+        "Vlan4000": {
+            "192.168.3.1/24": {
+                "etp11": [["192.168.3.2", "192.168.3.3"]]
+            }
+        },
         "Vlan6000": {
         }
     }
@@ -374,25 +420,29 @@ def test_construct_obj_for_template(mock_swsscommon_dbconnector_init, mock_parse
 @pytest.mark.parametrize("with_port_config", [True, False])
 @pytest.mark.parametrize("with_option_config", [True, False])
 def test_render_config(mock_swsscommon_dbconnector_init, mock_parse_port_map_alias, with_port_config,
-                       with_option_config):
+                       with_option_config, request):
     dhcp_db_connector = DhcpDbConnector()
     dhcp_cfg_generator = DhcpServCfgGenerator(dhcp_db_connector, "/usr/local/lib/kea/hooks/libdhcp_run_script.so",
                                               kea_conf_template_path="tests/test_data/kea-dhcp4.conf.j2")
     render_obj = copy.deepcopy(expected_render_obj)
-    expected_config = copy.deepcopy(expected_dhcp_config)
     if not with_port_config:
         render_obj["client_classes"] = []
         render_obj["subnets"] = []
-    elif not with_option_config:
-        render_obj["subnets"][0]["customized_options"] = {}
+        expected_config = copy.deepcopy(expected_dhcp_config_without_port_config)
+    else:
+        expected_config = copy.deepcopy(expected_dhcp_config)
+        if not with_option_config:
+            for i in range(len(expected_config["Dhcp4"]["subnet4"])):
+                render_obj["subnets"][i]["customized_options"] = {}
+        else:
+            for i in range(len(expected_config["Dhcp4"]["subnet4"])):
+                expected_config["Dhcp4"]["subnet4"][i]["option-data"].insert(0, {
+                                "name": "option223",
+                                "data": "dummy_value",
+                                "always-send": True
+                        })
     config = dhcp_cfg_generator._render_config(render_obj)
-    if with_option_config:
-        expected_config["Dhcp4"]["subnet4"][0]["option-data"].insert(0, {
-                        "name": "option223",
-                        "data": "dummy_value",
-                        "always-send": True
-                    })
-    assert json.loads(config) == expected_config if with_port_config else expected_config
+    assert json.loads(config) == expected_config
 
 
 def test_parse_customized_options(mock_swsscommon_dbconnector_init, mock_get_render_template,