Add service mark_dhcp_packet to mux container

files/build_templates/mux.service.j2

@@ -17,5 +17,15 @@ ExecStopPost=/usr/local/bin/write_standby.py
 Restart=always
 RestartSec=30
 
+[Service]
+User={{ sonicadmin_user }}
+ExecStartPre=/usr/local/bin/mark_dhcp_packet.py
+ExecStartPre=/usr/bin/{{docker_container_name}}.sh start
+ExecStart=/usr/bin/{{docker_container_name}}.sh wait
+ExecStop=/usr/bin/{{docker_container_name}}.sh stop
+ExecStopPost=/usr/local/bin/mark_dhcp_packet.py
+Restart=always
+RestartSec=30
+
 [Install]
 WantedBy=sonic.target

files/build_templates/sonic_debian_extension.j2

@@ -816,6 +816,9 @@ sudo LANG=C cp $SCRIPTS_DIR/sonic-netns-exec $FILESYSTEM_ROOT/usr/bin/sonic-netn
 # Copy write_standby script for mux state
 sudo LANG=C cp $SCRIPTS_DIR/write_standby.py $FILESYSTEM_ROOT/usr/local/bin/write_standby.py
 
+# Copy mark_dhcp_packet script
+sudo LANG=C cp $SCRIPTS_DIR/mark_dhcp_packet.py $FILESYSTEM_ROOT/usr/local/bin/mark_dhcp_packet.py
+
 # Copy systemd timer configuration
 # It implements delayed start of services
 sudo cp $BUILD_TEMPLATES/snmp.timer $FILESYSTEM_ROOT_USR_LIB_SYSTEMD_SYSTEM

files/scripts/mark_dhcp_packet.py

@@ -0,0 +1,108 @@
+#!/usr/bin/env python3
+
+import os
+import subprocess
+import sys
+import time
+
+from sonic_py_common import logger
+from swsscommon import swsscommon
+
+log = logger.Logger('mark_dhcp_packet')
+
+class MarkDhcpPacket(object):
+    """
+    Class used to configure dhcp packet mark in ebtables
+    """
+
+    def __init__(self):
+        self.config_db_connector = None
+        self.state_db_connector = None
+
+    @property
+    def config_db(self):
+        """
+        Returns config DB connector.
+        Initializes the connector during the first call
+        """
+        if self.config_db_connector is None:
+            self.config_db_connector = swsscommon.ConfigDBConnector()
+            self.config_db_connector.connect()
+
+        return self.config_db_connector
+
+    @property
+    def state_db(self):
+        """
+        Returns the state DB connector.
+        Initializes the connector during the first call
+        """
+        if self.state_db_connector is None:
+            self.state_db_connector = swsscommon.SonicV2Connector(host='127.0.0.1')
+            self.state_db_connector.connect(self.state_db_connector.STATE_DB)
+
+        return self.state_db_connector
+
+    @property
+    def is_dualtor(self):
+        """
+        Checks if script is running on a dual ToR system
+        """
+        localhost_key = self.config_db.get_keys('DEVICE_METADATA')[0]
+        metadata = self.config_db.get_entry('DEVICE_METADATA', localhost_key)
+
+        return 'subtype' in metadata and 'dualtor' in metadata['subtype'].lower()
+
+    def get_mux_intfs(self):
+        """
+        Returns a list of mux cable interfaces
+        """
+        mux_cables = self.config_db.get_table('MUX_CABLE')
+        mux_intfs = [intf for intf in mux_cables]
+
+        return mux_intfs
+
+    def generate_mark_from_index(self, index):
+        '''
+        type: string, format: hexadecimal
+        Example: 0x67001, 0x67002, ...
+        '''
+        intf_mark = "0x67" + str(index).zfill(3)
+
+        return intf_mark
+
+    def run_command(self, cmd):
+        subprocess.call(cmd, shell=True)
+        log.log_info("run command: {}".format(cmd))
+
+    def clear_dhcp_packet_marks(self):
+        '''
+        Flush the INPUT chain in ebtables upon restart
+        '''
+        self.run_command("sudo ebtables -F INPUT")
+
+    def apply_mark_in_ebtables(self, intf, mark):
+        self.run_command("sudo ebtables -A INPUT -i {} -j mark --mark-set {}".format(intf, mark))
+
+    def update_mark_in_state_db(self, intf, mark):
+        self.state_db.set(self.state_db.STATE_DB, 'DHCP_PACKET_MARK', intf, mark)
+
+    def apply_marks(self):
+        """
+        Writes dhcp packet marks in ebtables
+        """
+        if not self.is_dualtor:
+            return
+
+        self.clear_dhcp_packet_marks()
+
+        for (index, intf) in enumerate(self.get_mux_intfs(), 1):
+            mark = self.generate_mark_from_index(index)
+            self.apply_mark_in_ebtables(intf, mark)
+            self.update_mark_in_state_db(intf, mark)
+
+        log.log_info("Finish marking dhcp packets in ebtables.")
+
+if __name__ == '__main__':
+    mark_dhcp_packet = MarkDhcpPacket()
+    mark_dhcp_packet.apply_marks()