BFD (Bidirectional Forwarding Detection) is a protocol that operates at the interface and routing protocol levels and is designed to quickly detect failures between two neighboring routers, including interfaces, data links, and forwarding mechanisms. BFD operates over any data transmission protocol (network layer, link layer, tunnels, etc.) used between the two systems. BFD packets are transmitted as the payload of an encapsulating protocol suitable for the specific environment and network. BFD can operate at several levels of the system.
BFD routes exchange packets at a negotiated rate. If there are no incoming packets from a BFD-supporting router, that router is considered inoperative. BFD shares this information with the correspondent routing protocols, and the routing information is updated. BFD helps detect a single-end device failure and is used for the quick convergence of routing protocols.
A BFD profile is a configuration or a set of parameters used in dynamic routing protocols (BGP, OSPF) to define how the bidirectional forwarding detection functionality should work. Typically, a BFD profile includes parameters such as the desired detection time, hold time, and other parameters that determine the link fault detection speed and the response time of network devices in case of a fault.
Configuring and using profiles ensures prompt network fault detection, which helps speed up traffic rerouting to different interfaces and boost network reliability.
Configuring BFD for OSPF allows the corresponding BFD session connection events to instantly update the OSPF interface status.
In the case of BGP, BFD can also be used to regulate the failure detection time. Configuring BFD to detect link failures more quickly allows for faster response and improved BGP routing convergence.
To create a BFD profile, go to Libraries ➜ BFD profiles, click Add, and specify the desired settings:
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Name |
Description |
|---|---|
|
Name |
Set the BFD profile name. |
|
Detect multiplier |
Determine the detection time multiplier. The local system calculates the connection fault detection time as the product of a multiplier of the detection time received from the remote system and the agreed transmission interval of the remote system. If the BFD does not receive the control packet before the detection time expires, then the connection is considered to have failed. For example, if the transmission interval is 300 ms and the multiplier is 3, then the local system will detect failures only after 900 ms of no packets being received. |
|
Receive interval |
Configure the interval for receiving BFD control packets (the minimum time required between packets). The interval is not consistent between nodes. To determine the interval, each node compares its transmission interval with the reception interval of its neighbor - the larger of the two values is accepted as the transmission interval for this node. The default value is 50ms. |
|
Transmit interval |
Specify the transmission interval of BFD control packets; the interval must be consistent between nodes. The default value is 50ms. |
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Echo receive interval |
The minimum time interval after which the system will be able to receive echo packets. The default value is 50ms. |
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Echo transmit interval |
Configure the minimum transmission interval at which this system will be able to send BFD echo packets. The default value is 50ms. |
|
Echo mode |
Enable/disable Echo mode for data transmission. This mode is off by default. When the Echo feature is active, the BFD Echo packet stream is sent to the remote system, which returns them back along the same forwarding path. If a certain number of packets from the echo stream has not been received, the session is considered inoperative. The advantage of Echo mode is that it only tests the forwarding path on the remote system. This allows you to reduce the delay when passing the route and reduce the time spent detecting failures. The echo mode is not supported in multihop networks (see RFC 5883). |
|
Passive mode |
Enable or disable the Passive mode. When operating in the Passive mode, the system waits for control packets from neighbors and responds to them if they are received. This feature is useful when the router is central in a star-topology network, and you want to avoid unnecessary BFD control packets. By default, the Active mode is used. When operating in the Active mode, the node sends control packets to the neighboring node. Important! Both nodes cannot operate in the Passive mode. At least one of them (or both) must work in the Active mode. |
|
Minimum-ttl |
For multi-hop sessions only: configure the minimum lifetime value (number of hops) that BFD will accept in the BFD control packet. Can take values from 1 to 254. All packets with a lower TTL value will be discarded. Setting this value is necessary to set more stringent packet checking requirements to avoid receiving BFD control packets from other sessions. The default value is 254 (meaning that we expect only a single hop between the system and its peer). |