收集 Google Cloud Load Balancing 日志

支持的平台:

本文档介绍了如何通过启用将 Google Cloud 遥测数据提取到 Google 安全运营中心的功能来收集 Google Cloud 负载均衡日志,以及日志字段如何映射到 Google 安全运营中心 Unified Data Model (UDM) 字段。 本文档还列出了受支持的 Google Cloud Load Balancing 版本。

如需了解详情,请参阅将数据提取到 Google 安全运营中心

典型的部署包括启用 Google Security Operations 的 Google Cloud Load Balancing 日志。每个客户部署可能与此表示形式不同,并且可能更复杂。

该部署包含以下组件:

  • Google Cloud:您从中收集日志的 Google Cloud 服务和产品。

  • Google Cloud Load Balancing 日志:已启用以注入到 Google Security Operations 的 Google Cloud Load Balancing 日志。

  • Google Security Operations:Google Security Operations 会保留和分析来自 Google Cloud Load Balancing 的日志。

注入标签标识将原始日志数据标准化为结构化 UDM 格式的解析器。本文档中的信息适用于具有 GCP_LOADBALANCING 注入标签的解析器。

准备工作

  • 确保您使用的是 Google Cloud 负载均衡版本 1。

  • 确保部署架构中的所有系统都采用世界协调时间 (UTC) 时区进行配置。

配置 Google Cloud 以提取 Google Cloud Load Balancing 日志

如需将 Google Cloud 负载均衡日志注入 Google Security Operations,请按照将 Google Cloud 日志注入 Google Security Operations 页面上的步骤操作。

如果您在注入 Google Cloud Load Balancing 日志时遇到问题,请与 Google Security Operations 支持团队联系

字段映射参考文档

本部分介绍 Google Security Operations 解析器如何将 Google Cloud 负载均衡字段映射到 Google Security Operations 统一数据模型 (UDM) 字段。

字段映射参考信息:GCP_LOADBALANCING 日志字段到 UDM 字段

下表列出了 GCP_LOADBALANCING 日志类型的日志字段及其对应的 UDM 字段。

Log field UDM mapping Logic
receiveTimestamp metadata.collected_timestamp
timestamp metadata.event_timestamp
metadata.event_type If the following values are not empty, then the metadata.event_type UDM field is set to NETWORK_CONNECTION.
  • httpRequest.remoteIp
  • jsonPayload.remoteIp
  • jsonPayload.connection.clientIp
  • jsonPayload.clientInstance.vmIp
  • httpRequest.serverIp
  • jsonPayload.connection.serverIp
  • jsonPayload.serverInstance.vmIp


Else, if the following values are not empty, then the metadata.event_type UDM field is set to STATUS_UNCATEGORIZED.
  • httpRequest.remoteIp
  • jsonPayload.remoteIp
  • jsonPayload.connection.clientIp
  • jsonPayload.clientInstance.vmIp


Else, the metadata.event_type UDM field is set to GENERIC_EVENT.
logName metadata.product_event_type
insertId metadata.product_log_id
metadata.vendor_name The metadata.vendor_name UDM field is set to Google Cloud Platform.
httpRequest.protocol network.application_protocol If the httpRequest.requestUrl log field value matches the regular expression https or the httpRequest.protocol log field value matches the regular expression HTTPS, then the network.application_protocol UDM field is set to HTTPS.

Else, if the httpRequest.requestUrl log field value matches the regular expression http or the httpRequest.protocol log field value matches the regular expression HTTP, then the network.application_protocol UDM field is set to HTTP.
jsonPayload.clientLocation.asn network.asn
httpRequest.requestMethod network.http.method
httpRequest.referer network.http.referral_url
httpRequest.status network.http.response_code
httpRequest.userAgent network.http.user_agent
jsonPayload.connection.protocol network.ip_protocol If the jsonPayload.connection.protocol log field value is equal to 0, then the network.ip_protocol UDM field is set to UNKNOWN_IP_PROTOCOL.

Else, if the jsonPayload.connection.protocol log field value is equal to 1, then the network.ip_protocol UDM field is set to ICMP.

Else, if the jsonPayload.connection.protocol log field value is equal to 2, then the network.ip_protocol UDM field is set to IGMP.

Else, if the jsonPayload.connection.protocol log field value is equal to 6, then the network.ip_protocol UDM field is set to TCP.

Else, if the jsonPayload.connection.protocol log field value is equal to 17, then the network.ip_protocol UDM field is set to UDP.

Else, if the jsonPayload.connection.protocol log field value is equal to 41, then the network.ip_protocol UDM field is set to IP6IN4.

Else, if the jsonPayload.connection.protocol log field value is equal to 47, then the network.ip_protocol UDM field is set to GRE.

Else, if the jsonPayload.connection.protocol log field value is equal to 50, then the network.ip_protocol UDM field is set to ESP.

Else, if the jsonPayload.connection.protocol log field value is equal to 58, then the network.ip_protocol UDM field is set to ICMP6.

Else, if the jsonPayload.connection.protocol log field value is equal to 88, then the network.ip_protocol UDM field is set to EIGRP.

Else, if the jsonPayload.connection.protocol log field value is equal to 97, then the network.ip_protocol UDM field is set to ETHERIP.

Else, if the jsonPayload.connection.protocol log field value is equal to 103, then the network.ip_protocol UDM field is set to PIM.

Else, if the jsonPayload.connection.protocol log field value is equal to 112, then the network.ip_protocol UDM field is set to VRRP.

Else, if the jsonPayload.connection.protocol log field value is equal to 132, then the network.ip_protocol UDM field is set to SCTP.
httpRequest.responseSize network.received_bytes
jsonPayload.bytesReceived network.received_bytes
jsonPayload.packetsReceived network.received_packets
httpRequest.requestSize network.sent_bytes
jsonPayload.packetsSent network.sent_packets
jsonPayload.bytesSent network.sent_packets
jsonPayload.rtt network.session_duration.seconds Grok: Extracted sec from the log field jsonPayload.rtt and mapped it to the network.session_duration.seconds UDM field.
jsonPayload.rtt network.session_duration.nanos Grok: Extracted nano from the log field jsonPayload.rtt and mapped it to the network.session_duration.nanos UDM field.
jsonPayload.tls.cipher network.tls.cipher
jsonPayload.securityPolicyRequestData.tlsJa3Fingerprint network.tls.client.ja3
jsonPayload.tls.protocol network.tls.next_protocol
httpRequest.remoteIp principal.ip If the httpRequest.remoteIp log field value is not empty, then
Grok: Extracted ip and port from the log field httpRequest.remoteIp and mapped it to the principal.ip and principal.port UDM field respectively.
jsonPayload.remoteIp principal.ip If the jsonPayload.remoteIp log field value is not empty, then
Grok: Extracted ip and port from the log field jsonPayload.remoteIp and mapped it to the principal.ip and principal.port UDM field respectively.
jsonPayload.connection.clientIp principal.ip
clientInstance.vmIp principal.ip
jsonPayload.clientLocation.city principal.location.city
jsonPayload.clientLocation.regionCode principal.location.country_or_region
jsonPayload.securityPolicyRequestData.remoteIpInfo.regionCode principal.location.name
jsonPayload.clientLocation.subRegion principal.location.state
jsonPayload.connection.clientPort principal.port
jsonPayload.clientGkeDetails.cluster.clusterLocation principal.resource_ancestors.attribute.cloud.availability_zone
jsonPayload.clientVpc.projectId principal.resource_ancestors.name
jsonPayload.clientVpc.vpc principal.resource_ancestors.name
jsonPayload.clientVpc.subnetwork principal.resource_ancestors.name
jsonPayload.clientGkeDetails.cluster.cluster principal.resource_ancestors.name
jsonPayload.clientGkeDetails.pod.pod principal.resource_ancestors.name
jsonPayload.clientGkeDetails.service.service principal.resource_ancestors.name
jsonPayload.clientInstance.projectId principal.resource_ancestors.product_object_id
principal.resource_ancestors.resource_subtype If the jsonPayload.clientVpc.projectId log field value is not empty, then the principal.resource_ancestors.resource_subtype UDM field is set to clientVpc_projectId.

If the jsonPayload.clientVpc.vpc log field value is not empty, then the principal.resource_ancestors.resource_subtype UDM field is set to clientVpc_vpc.

If the jsonPayload.clientVpc.subnetwork log field value is not empty, then the principal.resource_ancestors.resource_subtype UDM field is set to clientVpc_subnetwork.

If the jsonPayload.clientGkeDetails.cluster.cluster log field value is not empty, then the principal.resource_ancestors.resource_subtype UDM field is set to clientGkeDetails_cluster.

If the jsonPayload.clientGkeDetails.pod.pod log field value is not empty, then the principal.resource_ancestors.resource_subtype UDM field is set to clientGkeDetails_pod.

If the jsonPayload.clientGkeDetails.service.service log field value is not empty, then the principal.resource_ancestors.resource_subtype UDM field is set to clientGkeDetails_service.
principal.resource_ancestors.resource_type If the jsonPayload.clientVpc.projectId log field value is not empty, then the principal.resource_ancestors.resource_type UDM field is set to VPC_NETWORK.

If the jsonPayload.clientVpc.vpc log field value is not empty, then the principal.resource_ancestors.resource_type UDM field is set to VIRTUAL_MACHINE.

If the jsonPayload.clientVpc.subnetwork log field value is not empty, then the principal.resource_ancestors.resource_type UDM field is set to VIRTUAL_MACHINE.

If the jsonPayload.clientGkeDetails.cluster.cluster log field value is not empty, then the principal.resource_ancestors.resource_type UDM field is set to CLUSTER.

If the jsonPayload.clientGkeDetails.pod.pod log field value is not empty, then the principal.resource_ancestors.resource_type UDM field is set to VIRTUAL_MACHINE.

If the jsonPayload.clientGkeDetails.service.service log field value is not empty, then the principal.resource_ancestors.resource_type UDM field is set to BACKEND_SERVICE.
jsonPayload.clientInstance.zone principal.resource.attribute.cloud.availability_zone
jsonPayload.clientInstance.vm principal.resource.name
principal.resource.resource_subtype If the jsonPayload.clientInstance.vm log field value is not empty, then the principal.resource.resource_subtype UDM field is set to client_instance_vm.
principal.resource.resource_type If the jsonPayload.clientInstance.vm log field value is not empty, then the principal.resource.resource_type UDM field is set to VIRTUAL_MACHINE.
security_result.action If the jsonPayload.enforcedSecurityPolicy.configuredAction log field value is equal to DENY, then the security_result.action UDM field is set to BLOCK.

Else, if the jsonPayload.enforcedSecurityPolicy.configuredAction log field value is equal to ALLOW, then the security_result.action UDM field is set to ALLOW.
If the jsonPayload.previewSecurityPolicy.configuredAction log field value is equal to DENY, then the security_result.action UDM field is set to BLOCK.

Else, if the jsonPayload.previewSecurityPolicy.configuredAction log field value is equal to ALLOW, then the security_result.action UDM field is set to ALLOW.
If the jsonPayload.enforcedEdgeSecurityPolicy.configuredAction log field value is equal to DENY, then the security_result.action UDM field is set to BLOCK.

Else, if the jsonPayload.enforcedEdgeSecurityPolicy.configuredAction log field value is equal to ALLOW, then the security_result.action UDM field is set to ALLOW.
If the jsonPayload.previewEdgeSecurityPolicy.configuredAction log field value is equal to DENY, then the security_result.action UDM field is set to BLOCK.

Else, if the jsonPayload.previewEdgeSecurityPolicy.configuredAction log field value is equal to ALLOW, then the security_result.action UDM field is set to ALLOW.
jsonPayload.enforcedSecurityPolicy.configuredAction security_result.action_details
jsonPayload.previewSecurityPolicy.configuredAction security_result.action_details
jsonPayload.enforcedEdgeSecurityPolicy.configuredAction security_result.action_details
jsonPayload.previewEdgeSecurityPolicy.configuredAction security_result.action_details
jsonPayload.enforcedSecurityPolicy.outcome security_result.outcomes[jsonpayload_enforcedsecuritypolicy_outcome]
jsonPayload.enforcedSecurityPolicy.priority security_result.priority_details
jsonPayload.previewSecurityPolicy.priority security_result.priority_details
jsonPayload.enforcedEdgeSecurityPolicy.priority security_result.priority_details
jsonPayload.previewEdgeSecurityPolicy.priority security_result.priority_details
jsonPayload.enforcedSecurityPolicy.name security_result.rule_name
jsonPayload.securityPolicyRequestData.recaptchaActionToken.score security_result.risk_score If the jsonPayload.securityPolicyRequestData.recaptchaActionToken.score log field value is not empty, then the jsonPayload.securityPolicyRequestData.recaptchaActionToken.score log field is mapped to the security_result.risk_score UDM field.
jsonPayload.securityPolicyRequestData.recaptchaSessionToken.score security_result.risk_score If the jsonPayload.securityPolicyRequestData.recaptchaSessionToken.score log field value is not empty, then the jsonPayload.securityPolicyRequestData.recaptchaSessionToken.score log field is mapped to the security_result.risk_score UDM field.
jsonPayload.previewSecurityPolicy.name security_result.rule_name
jsonPayload.enforcedEdgeSecurityPolicy.name security_result.rule_name
jsonPayload.previewEdgeSecurityPolicy.name security_result.rule_name
security_result.severity If the severity log field value matches the regular expression DEFAULT or DEBUG or INFO or NOTICE, then the security_result.severity UDM field is set to LOW.

Else, if the severity log field value matches the regular expression WARNING or ERROR, then the security_result.severity UDM field is set to MEDIUM.

Else, if the severity log field value matches the regular expression CRITICAL or ALERT or EMERGENCY, then the security_result.severity UDM field is set to HIGH.
severity security_result.severity_details
jsonPayload.statusDetails security_result.summary
jsonPayload.proxyStatus security_result.summary
resource.labels.backend_service_name target.application
resource.labels.backend_name target.group.group_display_name
resource.labels.backend_group_name target.group.group_display_name
httpRequest.serverIp target.ip
jsonPayload.connection.serverIp target.ip
serverInstance.vmIp target.ip
jsonPayload.connection.serverPort target.port
resource.labels.backend_scope target.resource_ancestors.attribute.cloud.availability_zone If the resource.labels.backend_target_name log field value is not empty, then the resource.labels.backend_scope log field is mapped to the target.resource_ancestors.attribute.cloud.availability_zone UDM field.
jsonPayload.serverInstance.zone target.resource_ancestors.attribute.cloud.availability_zone If the jsonPayload.serverInstance.vm log field value is not empty, then the jsonPayload.serverInstance.zone log field is mapped to the target.resource_ancestors.attribute.cloud.availability_zone UDM field.
jsonPayload.serverGkeDetails.cluster.clusterLocation target.resource_ancestors.attribute.cloud.availability_zone If the jsonPayload.serverGkeDetails.cluster.cluster log field value is not empty, then the jsonPayload.serverGkeDetails.cluster.clusterLocation log field is mapped to the target.resource_ancestors.attribute.cloud.availability_zone UDM field.
resource.labels.backend_zone target.resource_ancestors.attribute.cloud.availability_zone If the resource.labels.backend_zone log field value is not empty, then the resource.labels.backend_zone log field is mapped to the target.resource_ancestors.attribute.cloud.availability_zone UDM field.
resource.labels.backend_target_name target.resource_ancestors.name
jsonPayload.serverInstance.vm target.resource_ancestors.name
jsonPayload.serverGkeDetails.cluster.cluster target.resource_ancestors.name
jsonPayload.serverGkeDetails.pod.pod target.resource_ancestors.name
jsonPayload.serverGkeDetails.service.service target.resource_ancestors.name
resource.labels.network_name target.resource_ancestors.name
resource.labels.project_id target.resource_ancestors.product_object_id
jsonPayload.serverInstance.projectId target.resource_ancestors.product_object_id If the jsonPayload.serverInstance.vm log field value is not empty, then the jsonPayload.serverInstance.projectId log field is mapped to the target.resource_ancestors.product_object_id UDM field.
resource.labels.project target.resource_ancestors.product_object_id
resource.labels.backend_target_type target.resource_ancestors.resource_subtype If the resource.labels.backend_target_name log field value is not empty, then the resource.labels.backend_target_type log field is mapped to the target.resource_ancestors.resource_subtype UDM field.

If the jsonPayload.serverInstance.vm log field value is not empty, then the target.resource_ancestors.resource_subtype UDM field is set to serverInstance_vm.

If the jsonPayload.serverGkeDetails.cluster.cluster log field value is not empty, then the target.resource_ancestors.resource_subtype UDM field is set to serverGkeDetails_cluster.

If the jsonPayload.serverGkeDetails.pod.pod log field value is not empty, then the target.resource_ancestors.resource_subtype UDM field is set to serverGkeDetails_pod.

If the jsonPayload.serverGkeDetails.service.service log field value is not empty, then the target.resource_ancestors.resource_subtype UDM field is set to serverGkeDetails_service.

If the resource.labels.network_name log field value is not empty, then the target.resource_ancestors.resource_subtype UDM field is set to network_name.
target.resource_ancestors.resource_type If the resource.labels.backend_target_name log field value is not empty, then the target.resource_ancestors.resource_type UDM field is set to BACKEND_SERVICE.

If the jsonPayload.serverInstance.vm log field value is not empty, then the target.resource_ancestors.resource_type UDM field is set to VIRTUAL_MACHINE.

If the jsonPayload.serverGkeDetails.cluster.cluster log field value is not empty, then the target.resource_ancestors.resource_type UDM field is set to CLUSTER.

If the jsonPayload.serverGkeDetails.pod.pod log field value is not empty, then the target.resource_ancestors.resource_type UDM field is set to VIRTUAL_MACHINE.

If the jsonPayload.serverGkeDetails.service.service log field value is not empty, then the target.resource_ancestors.resource_type UDM field is set to BACKEND_SERVICE.

If the resource.labels.network_name log field value is not empty, then the target.resource_ancestors.resource_type UDM field is set to VPC_NETWORK.
resource.labels.region target.resource.attribute.cloud.availability_zone
resource.labels.endpoint_zone target.resource.attribute.cloud.availability_zone
resource.labels.zone target.resource.attribute.cloud.availability_zone
target.resource.attribute.cloud.environment The target.resource.attribute.cloud.environment UDM field is set to GOOGLE_CLOUD_PLATFORM.
resource.labels.load_balancer_name target.resource.name
resource.type target.resource.resource_subtype
target.resource.resource_type The target.resource.resource_type UDM field is set to DEVICE.
httpRequest.requestUrl target.url
jsonPayload.backendTargetProjectNumber about.labels[backend_target_project_number] (deprecated)
jsonPayload.backendTargetProjectNumber additional.fields[backend_target_project_number]
jsonPayload.cacheDecision about.labels[cache_decision]
jsonPayload.cacheId about.labels[cache_id] (deprecated)
jsonPayload.cacheId additional.fields[cache_id]
jsonPayload.endTime about.labels[end_time] (deprecated)
jsonPayload.endTime additional.fields[end_time]
jsonPayload.@type about.labels[metadata_type] (deprecated)
jsonPayload.@type additional.fields[metadata_type]
spanId about.labels[span_id] (deprecated)
spanId additional.fields[span_id]
jsonPayload.startTime about.labels[start_time] (deprecated)
jsonPayload.startTime additional.fields[start_time]
traceSampled about.labels[trace_sampled] (deprecated)
traceSampled additional.fields[trace_sampled]
trace about.labels[trace] (deprecated)
trace additional.fields[trace]
jsonPayload.clientLocation.continent principal.labels[client_loacation_continent] (deprecated)
jsonPayload.clientLocation.continent additional.fields[client_loacation_continent]
jsonPayload.networkTier.networkTier principal.labels[network_tier] (deprecated)
jsonPayload.networkTier.networkTier additional.fields[network_tier]
jsonPayload.clientGkeDetails.pod.podNamespace principal.resource_ancestors.attribute.labels[pod_namespace]
jsonPayload.clientGkeDetails.service.serviceNamespace principal.resource_ancestors.attribute.labels[service_namespace]
jsonPayload.clientInstance.region principal.resource.attribute.labels[client_instance_region]
resource.labels.forwarding_rule_name security_result.rule_labels[forwarding_rule_name]
jsonPayload.enforcedSecurityPolicy.matchedFieldName security_result.rule_labels[matched_field_name]
jsonPayload.enforcedSecurityPolicy.matchedFieldType security_result.rule_labels[matched_field_type]
jsonPayload.enforcedSecurityPolicy.matchedFieldValue security_result.rule_labels[matched_field_value]
jsonPayload.enforcedSecurityPolicy.matchedLength security_result.rule_labels[matched_length]
jsonPayload.enforcedSecurityPolicy.preconfiguredExprIds security_result.rule_labels[preconfigured_expr_ids]
jsonPayload.enforcedSecurityPolicy.threatIntelligence.categories security_result.rule_labels[threat_intelligence_category]
resource.labels.backend_group_scope target.group.attribute.labels[backend_group_scope]
resource.labels.backend_group_type target.group.attribute.labels[backend_group_type]
resource.labels.backend_type target.group.attribute.labels[backend_type]
resource.labels.forwarding_rule_network_tier target.labels[forwarding_rule_network_tier] (deprecated)`
resource.labels.forwarding_rule_network_tier additional.fields[forwarding_rule_network_tier]
httpRequest.cacheFillBytes target.labels[http_request_cache_fill_bytes] (deprecated)
httpRequest.cacheFillBytes additional.fields[http_request_cache_fill_bytes]
httpRequest.cacheHit target.labels[http_request_cache_hit] (deprecated)
httpRequest.cacheHit additional.fields[http_request_cache_hit]
httpRequest.cacheLookup target.labels[http_request_cache_lookup] (deprecated)
httpRequest.cacheLookup additional.fields[http_request_cache_lookup]
httpRequest.cacheValidatedWithOriginServer target.labels[http_request_cache_validated_with_origin_server] (deprecated)
httpRequest.cacheValidatedWithOriginServer additional.fields[http_request_cache_validated_with_origin_server]
httpRequest.latency target.labels[http_request_latency] (deprecated)
httpRequest.latency additional.fields[http_request_latency]
resource.labels.primary_target_pool target.labels[primary_target_pool] (deprecated)
resource.labels.primary_target_pool additional.fields[primary_target_pool]
resource.labels.target_pool target.labels[target_pool] (deprecated)
resource.labels.target_pool additional.fields[target_pool]
resource.labels.target_proxy_name target.labels[target_proxy_name] (deprecated)
resource.labels.target_proxy_name additional.fields[target_proxy_name]
resource.labels.url_map_name target.labels[url_map_name] (deprecated)
resource.labels.url_map_name additional.fields[url_map_name]
resource.labels.backend_failover_configuration target.resource_ancestors.attribute.labels[backend_failover_configuration]
resource.labels.backend_network_name target.resource_ancestors.attribute.labels[backend_network_name]
resource.labels.backend_scope_type target.resource_ancestors.attribute.labels[backend_scope_type]
resource.labels.backend_subnetwork_name target.resource_ancestors.attribute.labels[backend_subnetwork_name]
jsonPayload.serverInstance.region target.resource_ancestors.attribute.labels[client_instance_region]
jsonPayload.serverGkeDetails.pod.podNamespace target.resource_ancestors.attribute.labels[pod_namespace]
jsonPayload.serverGkeDetails.service.serviceNamespace target.resource_ancestors.attribute.labels[service_namespace]
resource.labels.matched_url_path_rule target.resource.attribute.labels[matched_url_path_rule]
resource.labels.loadbalancing_scheme_name target.resource.attribute.labels[loadbalancing_scheme_name]
jsonPayload.enforcedSecurityPolicy.rateLimitAction.key security_result.rule_labels[enforcedsecuritypolicy_ratelimitaction_key]
jsonPayload.enforcedSecurityPolicy.rateLimitAction.outcome security_result.rule_labels[enforcedsecuritypolicy_ratelimitaction_outcome]
jsonPayload.enforcedSecurityPolicy.adaptiveProtection.autoDeployAlertId security_result.rule_labels[adaptiveprotection_autodeployalertid]
jsonPayload.previewSecurityPolicy.rateLimitAction.key security_result.rule_labels[previewsecuritypolicy_ratelimitaction_key]
jsonPayload.previewSecurityPolicy.rateLimitAction.outcome security_result.rule_labels[previewsecuritypolicy_ratelimitaction_outcome]
jsonPayload.previewSecurityPolicy.outcome security_result.outcomes[previewsecuritypolicy_outcome]
jsonPayload.previewSecurityPolicy.preconfiguredExprIds security_result.rule_labels[previewsecuritypolicy_preconfigured_expr_ids]
jsonPayload.enforcedEdgeSecurityPolicy.outcome security_result.outcomes[enforcededgesecuritypolicy_outcome]
jsonPayload.previewEdgeSecurityPolicy.outcome security_result.outcomes[previewedgesecuritypolicy_outcome]

后续步骤