text: #!/usr/bin/env python3
  #
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  #
  import unittest
  
  import config
  import thread_cert
  
  # Test description:
  #   This test verifies that a single NAT64 prefix is advertised when there are
  #   multiple Border Routers in the same Thread and infrastructure network.
  #
  #   TODO: add checks for outbound connectivity from Thread device to IPv4 host
  #         after OTBR change is ready.
  #
  # Topology:
  #    ----------------(eth)--------------------------
  #           |                 |             |
  #          BR1 (Leader) ---- BR2           HOST
  #           |
  #        ROUTER
  #
  
  BR1 = 1
  ROUTER = 2
  BR2 = 3
  HOST = 4
  
  
  class Nat64MultiBorderRouter(thread_cert.TestCase):
      USE_MESSAGE_FACTORY = False
  
      TOPOLOGY = {
          BR1: {
              'name': 'BR1',
              'allowlist': [ROUTER, BR2],
              'is_otbr': True,
              'version': '1.2',
          },
          ROUTER: {
              'name': 'Router',
              'allowlist': [BR1],
              'version': '1.2',
          },
          BR2: {
              'name': 'BR2',
              'allowlist': [BR1],
              'is_otbr': True,
              'version': '1.2'
          },
          HOST: {
              'name': 'Host',
              'is_host': True
          },
      }
  
      def test(self):
          br1 = self.nodes[BR1]
          router = self.nodes[ROUTER]
          br2 = self.nodes[BR2]
          host = self.nodes[HOST]
  
          host.start(start_radvd=False)
          self.simulator.go(5)
  
          br1.start()
          self.simulator.go(config.BORDER_ROUTER_STARTUP_DELAY)
          self.assertEqual('leader', br1.get_state())
  
          router.start()
          self.simulator.go(config.ROUTER_STARTUP_DELAY)
          self.assertEqual('router', router.get_state())
  
          #
          # Case 1. BR2 joins the network later and it will not add
          #         its local nat64 prefix to Network Data.
          #
          br2.start()
          self.simulator.go(config.BORDER_ROUTER_STARTUP_DELAY)
          self.assertEqual('router', br2.get_state())
  
          # Only 1 NAT64 prefix in Network Data.
          self.simulator.go(30)
          self.assertEqual(len(br1.get_netdata_nat64_prefix()), 1)
          self.assertEqual(len(br2.get_netdata_nat64_prefix()), 1)
          self.assertEqual(br1.get_netdata_nat64_prefix()[0], br2.get_netdata_nat64_prefix()[0])
          nat64_prefix = br1.get_netdata_nat64_prefix()[0]
  
          # The NAT64 prefix in Network Data is same as BR1's local NAT64 prefix.
          br1_nat64_prefix = br1.get_br_nat64_prefix()
          br2_nat64_prefix = br2.get_br_nat64_prefix()
          self.assertEqual(nat64_prefix, br1_nat64_prefix)
          self.assertNotEqual(nat64_prefix, br2_nat64_prefix)
  
          #
          # Case 2. Disable and re-enable border routing on BR1.
          #
          br1.disable_br()
          self.simulator.go(30)
  
          # BR1 withdraws its prefix and BR2 advertises its prefix.
          self.assertEqual(len(br1.get_netdata_nat64_prefix()), 1)
          self.assertEqual(br2_nat64_prefix, br1.get_netdata_nat64_prefix()[0])
          self.assertNotEqual(br1_nat64_prefix, br1.get_netdata_nat64_prefix()[0])
  
          br1.enable_br()
          self.simulator.go(config.BORDER_ROUTER_STARTUP_DELAY)
  
          # NAT64 prefix in Network Data is still advertised by BR2.
          self.assertEqual(len(br1.get_netdata_nat64_prefix()), 1)
          self.assertEqual(br2_nat64_prefix, br1.get_netdata_nat64_prefix()[0])
          self.assertNotEqual(br1_nat64_prefix, br1.get_netdata_nat64_prefix()[0])
  
  
  if __name__ == '__main__':
      unittest.main()
  