Fix to use IPv6 linklocal address as snmp agent address (sonic-net#3215)

What I did
If link local IPv6 address is added as SNMP agent address, it will fail.
This PR requires changes in snmpd.conf.j2 template here sonic-net/sonic-buildimage#18350

How I did it
Append scope id to ipv6 link local IP address.

How to verify it
Able to configure link local ipv6 address as snmp agent address
sudo config snmpagentaddress add fe80::a%eth0

config/main.py

@@ -3498,7 +3498,10 @@ def add_snmp_agent_address(ctx, agentip, port, vrf):
     """Add the SNMP agent listening IP:Port%Vrf configuration"""
 
     #Construct SNMP_AGENT_ADDRESS_CONFIG table key in the format ip|<port>|<vrf>
-    if not clicommon.is_ipaddress(agentip):
+    # Link local IP address should be provided along with zone id
+    # <link_local_ip>%<zone_id> for ex fe80::1%eth0
+    agent_ip_addr = agentip.split('%')[0]
+    if not clicommon.is_ipaddress(agent_ip_addr):
         click.echo("Invalid IP address")
         return False
     config_db = ctx.obj['db']
@@ -3508,7 +3511,7 @@ def add_snmp_agent_address(ctx, agentip, port, vrf):
             click.echo("ManagementVRF is Enabled. Provide vrf.")
             return False
     found = 0
-    ip = ipaddress.ip_address(agentip)
+    ip = ipaddress.ip_address(agent_ip_addr)
     for intf in netifaces.interfaces():
         ipaddresses = netifaces.ifaddresses(intf)
         if ip_family[ip.version] in ipaddresses:

tests/config_snmp_test.py

@@ -877,6 +877,34 @@ def test_config_snmp_community_add_new_community_with_invalid_type_yang_validati
         assert result.exit_code != 0
         assert 'SNMP community configuration failed' in result.output
 
+    @patch('netifaces.interfaces', mock.Mock(return_value=['eth0']))
+    @patch('netifaces.ifaddresses', mock.Mock(return_value={2:
+                                              [{'addr': '10.1.0.32', 'netmask': '255.255.255.0',
+                                                'broadcast': '10.1.0.255'}],
+                                                10: [{'addr': 'fe80::1%eth0', 'netmask': 'ffff:ffff:ffff:ffff::/64'}]}))
+    @patch('os.system', mock.Mock(return_value=0))
+    def test_config_snmpagentaddress_add_linklocal(self):
+        db = Db()
+        obj = {'db': db.cfgdb}
+        runner = CliRunner()
+        runner.invoke(config.config.commands["snmpagentaddress"].commands["add"], ["fe80::1%eth0"], obj=obj)
+        assert ('fe80::1%eth0', '', '') in db.cfgdb.get_keys('SNMP_AGENT_ADDRESS_CONFIG')
+        assert db.cfgdb.get_entry("SNMP_AGENT_ADDRESS_CONFIG", "fe80::1%eth0||") == {}
+
+    @patch('netifaces.interfaces', mock.Mock(return_value=['eth0']))
+    @patch('netifaces.ifaddresses', mock.Mock(return_value={2:
+                                              [{'addr': '10.1.0.32', 'netmask': '255.255.255.0',
+                                                'broadcast': '10.1.0.255'}],
+                                                10: [{'addr': 'fe80::1', 'netmask': 'ffff:ffff:ffff:ffff::/64'}]}))
+    @patch('os.system', mock.Mock(return_value=0))
+    def test_config_snmpagentaddress_add_ipv4(self):
+        db = Db()
+        obj = {'db': db.cfgdb}
+        runner = CliRunner()
+        runner.invoke(config.config.commands["snmpagentaddress"].commands["add"], ["10.1.0.32"], obj=obj)
+        assert ('10.1.0.32', '', '') in db.cfgdb.get_keys('SNMP_AGENT_ADDRESS_CONFIG')
+        assert db.cfgdb.get_entry("SNMP_AGENT_ADDRESS_CONFIG", "10.1.0.32||") == {}
+
     @classmethod
     def teardown_class(cls):
         print("TEARDOWN")