静态建立BFD会话静态建立BFD会话是指通过命令行手动

一、开始

静态路由是否能够加入到全局路由表中并成功指导报文正确转发,取决于其出接口状态与下一跳可达性，以及相关检测联动的状态等方面。因此静态路由定位故障的思路是:首先查看全局路由表中是否有该静态路由；然后据此相应地检查出接口状态、下一跳可达性、BFD/NQA配置、路由优先级等。

网络管理中，总希望当网络中一些关键链路或关键节点发生故障时能及时获得提示信息，并能自动进行相应的处理。

BFD（双向转发检测）和NQA（网络质量分析）就能实现这样的功能。BFD不仅可以检测直连链路（“单跳”）的故障，还可以检测非直连链路（“多跳”）的故障，还可以与多种功能进行联动，如与接口状态、静态路由、RIP路由、OSPF路由、IS-IS路由、BGP路由、VRRP等，在检测到故障后，上送到对应的上层应用模块进行快速处理。如与接口状态联动时会把相应的接口状态由Up转为Down；与路由联动可以使这些路由模块进行重新拓扑计算，实现快速网络收敛；与VRRP联动时可以快速切换到备用线路上。NQA可以实时监视网络性能，

在网络发生故障时进行故障诊断和定位。NQA支持DHCP测试、DNS测试、FTP测试、HTTP测试、ICMP测试、SNMP测试、TCP测试和Trace测试等。NQA通过发送测试报文，对网络性能或服务质量进行分析，为用户提供网络性能参数。BFD基础BFD（Bidirectional Forwarding Detection，双向转发检测）用于快速检测系统之间的发送和接收两个方向的通信故障，并在出现故障时通知上层应用。与其他功能联动，联动是指使对应接口状态或者路由协议、VRRP等可根据BFD会话状态进行对应的接口状态改变、路由收敛和VRRP主备切换等。

一、BFD概述在现有网络中，有些链路通常是通过硬件检测信号（如SDH告警）来检测链路故障，硬件检测速度快，但不是所有介质都能够提供硬件检测功能。

有的依靠上层协议（如各种路由协议）自身的Hello报文机制来进行故障检测的，但检测时间在1s以上。BFD是一种通用的、标准化的与介质和协议均无关的快速链路故障检测机制，可为各上层协议统一的快速检测两台路由器间（不一定是直接连接的）

双向转发路径的故障。二、BFD检测原理BFD可在两台网络设备间建立用来监测设备间双向转发路径的BFD会话，为上层应用服务。BFD本身没有邻居发现机制，而是靠被服务的上层应用通知其邻居信息以建立会话。会话建立后会周期性的快速发送BFD报文，如果在检测时间内没有收到BFD报文则认为该双向路径发生了故障。

1、BFD会话建立流程BFD会话建立有两种方式，即静态建立BFD会话和动态建立BFD会话。其主要区别在于本地标识符（Local Discrimination）和远端标识符（Remote Discrimination）的配置方式不同。标识符是用来标识对应BFD会话中本地和远端实体的数字标识，BFD通过控制报文中的本地标识符和远端标识符区分不同的BFD会话。这个“本地”和“远端”是相对的，本地配置的远端标识符就是对端配置的本地标识符，

本地配置的本地标识符就是对端配置的远端标识符。

https://weibo.com/ttarticle/p/show?id=2309405162890574299397

https://weibo.com/ttarticle/p/show?id=2309405163020786466912

https://weibo.com/ttarticle/p/show?id=2309405163020786466906

https://weibo.com/ttarticle/p/show?id=2309405163020816089363

https://weibo.com/ttarticle/p/show?id=2309405163020979667187

https://weibo.com/ttarticle/p/show?id=2309405163020988055650

https://weibo.com/ttarticle/p/show?id=2309405163021000376574

https://weibo.com/ttarticle/p/show?id=2309405163021117816883

https://weibo.com/ttarticle/p/show?id=2309405163021172604943

https://weibo.com/ttarticle/p/show?id=2309405163021176537176

https://weibo.com/ttarticle/p/show?id=2309405163021314949125

https://weibo.com/ttarticle/p/show?id=2309405163021424263398

https://weibo.com/ttarticle/p/show?id=2309405163021637910686

https://weibo.com/ttarticle/p/show?id=2309405163021696893238

https://weibo.com/ttarticle/p/show?id=2309405163021717864774

https://weibo.com/ttarticle/p/show?id=2309405163021743030664

https://weibo.com/ttarticle/p/show?id=2309405163021822722562

https://weibo.com/ttarticle/p/show?id=2309405163021889831110

https://weibo.com/ttarticle/p/show?id=2309405163021906608608

https://weibo.com/ttarticle/p/show?id=2309405163021973455056

https://weibo.com/ttarticle/p/show?id=2309405163022011465896

https://weibo.com/ttarticle/p/show?id=2309405163022078574900

https://weibo.com/ttarticle/p/show?id=2309405163022095089881

https://weibo.com/ttarticle/p/show?id=2309405163022170849577

https://weibo.com/ttarticle/p/show?id=2309405163022384759262

https://weibo.com/ttarticle/p/show?id=2309405163022405468402

https://weibo.com/ttarticle/p/show?id=2309405163022426439914

https://weibo.com/ttarticle/p/show?id=2309405163022498005303

https://weibo.com/ttarticle/p/show?id=2309405163022569046258

https://weibo.com/ttarticle/p/show?id=2309405163022619639836

https://weibo.com/ttarticle/p/show?id=2309405163022669709533

https://weibo.com/ttarticle/p/show?id=2309405163022753595689

https://weibo.com/ttarticle/p/show?id=2309405163022770635190

https://weibo.com/ttarticle/p/show?id=2309405163022837743674

https://weibo.com/ttarticle/p/show?id=2309405163022930018537

https://weibo.com/ttarticle/p/show?id=2309405163023341060178

https://weibo.com/ttarticle/p/show?id=2309405163023403712600

https://weibo.com/ttarticle/p/show?id=2309405163023517220956

https://weibo.com/ttarticle/p/show?id=2309405163023533735974

https://weibo.com/ttarticle/p/show?id=2309405163023588524271

https://weibo.com/ttarticle/p/show?id=2309405163023751839988

https://weibo.com/ttarticle/p/show?id=2309405163023773073709

https://weibo.com/ttarticle/p/show?id=2309405163023798239317

https://weibo.com/ttarticle/p/show?id=2309405163023995371692

https://weibo.com/ttarticle/p/show?id=2309405163024251224386

https://weibo.com/ttarticle/p/show?id=2309405163024268001377

https://weibo.com/ttarticle/p/show?id=2309405163024309944363

https://weibo.com/ttarticle/p/show?id=2309405163024439968116

https://weibo.com/ttarticle/p/show?id=2309405163024515203124

https://weibo.com/ttarticle/p/show?id=2309405163024632905872

https://weibo.com/ttarticle/p/show?id=2309405163024741958064

https://weibo.com/ttarticle/p/show?id=2309405163024880370020

https://weibo.com/ttarticle/p/show?id=2309405163033004736739

https://weibo.com/ttarticle/p/show?id=2309405163033008668727

https://weibo.com/ttarticle/p/show?id=2309405163033050874236

https://weibo.com/ttarticle/p/show?id=2309405163033063457056

https://weibo.com/ttarticle/p/show?id=2309405163033206063312

https://weibo.com/ttarticle/p/show?id=2309405163033231229111

https://weibo.com/ttarticle/p/show?id=2309405163033277366537

https://weibo.com/ttarticle/p/show?id=2309405163033289687199

https://weibo.com/ttarticle/p/show?id=2309405163028382613781

https://weibo.com/ttarticle/p/show?id=2309405163028483014668

https://weibo.com/ttarticle/p/show?id=2309405163028575289658

https://weibo.com/ttarticle/p/show?id=2309405163028676214976

https://weibo.com/ttarticle/p/show?id=2309405163028776878350

https://weibo.com/ttarticle/p/show?id=2309405163028873347466

https://weibo.com/ttarticle/p/show?id=2309405163028969554110

https://weibo.com/ttarticle/p/show?id=2309405163029149909000

https://weibo.com/ttarticle/p/show?id=2309405163029267611751

https://weibo.com/ttarticle/p/show?id=2309405163029590573442

https://weibo.com/ttarticle/p/show?id=2309405163029728723182

https://weibo.com/ttarticle/p/show?id=2309405163029997421053

https://weibo.com/ttarticle/p/show?id=2309405163030152347897

https://weibo.com/ttarticle/p/show?id=2309405163030303604968

https://weibo.com/ttarticle/p/show?id=2309405163030450405385

https://weibo.com/ttarticle/p/show?id=2309405163030588555441

https://weibo.com/ttarticle/p/show?id=2309405163030693675354

https://weibo.com/ttarticle/p/show?id=2309405163030794338611

https://weibo.com/ttarticle/p/show?id=2309405163031188603026

https://weibo.com/ttarticle/p/show?id=2309405163031301849359

https://weibo.com/ttarticle/p/show?id=2309405163031490330636

https://weibo.com/ttarticle/p/show?id=2309405163031586799803

https://weibo.com/ttarticle/p/show?id=2309405163031683531116

https://weibo.com/ttarticle/p/show?id=2309405163031784194069

https://weibo.com/ttarticle/p/show?id=2309405163031876469062

https://weibo.com/ttarticle/p/show?id=2309405163031968743683

https://weibo.com/ttarticle/p/show?id=2309405163032295637052

https://weibo.com/ttarticle/p/show?id=2309405163032383979859

https://weibo.com/ttarticle/p/show?id=2309405163032480186415

https://weibo.com/ttarticle/p/show?id=2309405163032790827429

https://weibo.com/ttarticle/p/show?id=2309405163032950210874

https://weibo.com/ttarticle/p/show?id=2309405163033109594360

https://weibo.com/ttarticle/p/show?id=2309405163033214451776

https://weibo.com/ttarticle/p/show?id=2309405163033373573393

https://weibo.com/ttarticle/p/show?id=2309405163033541345314

（1）静态建立BFD会话静态建立BFD会话是指通过命令行手动配置BFD会话参数，包括配置本地标识符和远端标识符等，然后手工下发BFD会话建立请求。建立静态BFD会话又包括两种方式①手动指定标识符的静态BFD会话必须手动指定BFD会话的本地标识符和远端标识符。②标识符自协商的静态BFD会话如果对端设备采用动态BFD，而本端设备既要与之互通，又要能够实现BFD检测静态路由，则必须配置静态标识符自协商BFD。这种BFD会话方式无需指定本地标识符和远端标识符。本端采用静态标识

（2）动态建立BFD会话动态BFD联动主要是由各种路由协议触发的。在建立动态BFD会话时，系统对本地标识符和远端标识符分别采用如下处理方式：①动态分配本地标识符当应用程序触发动态建立BFD会话时，系统分配本地动态会话标识符区域中可用的一个标识值作为本次BFD会话的本地标识符，然后向对端发送远端标识符的值为0的BFD控制报文（之所以采用0来标识远端标识符，是因为在静态标识符配置中0是保留不能配置的），进行会话协商。②自动学习远端标识符当BFD会话的另一端收到远端标识符的值为0的BFD控制报文，判断该报文是否与本地BFD会话匹配（查看0号标识符是否已被占用），如果匹配，则学习接收到的BFD本地标识符的值，以获取远端标识符，否则中断BFD会话。这种BFD会话方式主要用于与动态路由协议的联动中，并且同一时刻、同一链路只允许建立一组BFD会话。