code: def _snat_subnet_for_ext_net(self, context, subnet, net):
          
          if subnet['network_id'] == net['id']:
              return True
  
          network = self._core_plugin.get_network(
              context.elevated(), subnet['network_id'])
          ext_net_name = network['name']
          if (APIC_SNAT_NET + '-') in ext_net_name:
              # This is APIC ML2 mode -- we need to strip the prefix
              ext_net_name = ext_net_name[len(APIC_SNAT_NET + '-'):]
              if net['id'] == ext_net_name:
                  return True
          return False
docs: Determine if an SNAT subnet is for this external network.
  
          This method determines if a given SNAT subnet is intended for
          the passed external network.
  
          For APIC ML2/Neutron workflow, SNAT subnets are created on
          a separate network from the external network. The association
          with an external network is made by putting the name of the
          external network in the name of the SNAT network name, using
          a well-known prefix.