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The function of BFD

In this time, we introduce a more interesting and extremely useful content, BFD(Bidirectional Forwarding Detection.It is a unified detection mechanism for the entire network. It is used to quickly detect and monitor the forwarding and connectivity of links or IP routes in the network.

With the widespread deployment of network applications, network outages may affect business operations and cause significant losses.
In order to reduce the impact of link and device failures on services and improve network reliability, network devices need to detect communication failures with neighboring devices as soon as possible in order to take timely measures to ensure normal business operations. At the same time, in order to protect critical applications, a certain redundant backup link will be designed in the network. When a network failure occurs, it is required that network equipment can quickly detect the failure and switch traffic to the backup link to speed up network convergence .

Although many protocols provide monitoring mechanisms such as keepalive and hello, as well as many protocols. For example, OSPF and ISIS provide a fast Hello mechanism, but the detection can only reach 1 second accuracy, and the fast Hello mechanism is only implemented for this protocol and cannot be provided to other protocols. In this case, BFD is required. BFD can associate with static routing, dynamic protocols, VRRP and other protocols to achieve fast detection and switchover.

BFD basic implementation principle:

  1. After the BFD session is established, BFD packets are sent quickly and periodically. If the peer BFD packet is not received within the detection time, the bidirectional forwarding path is considered to be faulty, and the relevant layer application being serviced is notified to handle it accordingly .
  2. BFD itself does not have a neighbor discovery mechanism. Instead, the upper-layer application being served notifies its neighbor information to establish a session.


BFD provides a standardized fast fault detection mechanism that is independent of media and upper layer protocols. BFD has the following advantages:

  1. Perform bidirectional fault detection on the link between two network nodes. The link can be a physical link or a logical link.

(Such as LSP, tunnel, etc.)

2.It can provide fault detection services for different upper-layer applications (such as MPLS, OSPF, IS-IS, etc.) and provide the same fault detection time.

3.BFD’s fault detection time is far less than 1 second, which can accelerate network convergence faster, reduce the time of upper-layer application interruption, and improve network reliability and service quality.

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