Bidirectional forwarding detection (BFD) provides a general-purpose, standard, medium- and protocol-independent fast failure detection mechanism. It can detect and monitor the connectivity of forwarding paths to detect communication failures quickly so that measures can be taken to ensure service continuity and enhance network availability.

BFD can uniformly and quickly detect the failures of the bidirectional forwarding paths between two devices for upper-layer protocols such as routing protocols. The hello mechanism used by upper-layer protocols needs seconds to detect a link failure, while BFD can provide detection measured in milliseconds.

Single-hop detection and multihop detection

BFD can be used for single-hop and multihop detections.

· Single-hop detection—Detects the IP connectivity between two directly connected systems.

· Multihop detection—Detects any of the paths between two systems. These paths have multiple hops, and might overlap.

BFD session modes

BFD sessions use echo packets and control packets.

Echo packet mode

Echo packets are encapsulated into UDP packets with port number 3785.

The local end of the link sends echo packets to establish BFD sessions and monitor link status. The peer end does not establish BFD sessions and only forwards the packets back to the originating end. If the local end does not receive echo packets from the peer end within the detection time, it considers the session to be down.

In echo packet mode, BFD supports only single-hop detection and the BFD sessions are independent of the operating mode.

Control packet mode

Control packets are encapsulated into UDP packets with port number 3784 for single-hop detection or port number 4784 for multihop detection.

The two ends of the link negotiate the establishment of BFD sessions by using the session parameters carried in control packets. Session parameters include session discriminators, desired minimum packet sending and receiving intervals, and local BFD session state.

Both ends of the link exchange BFD control packets to monitor link status.

Before a BFD session is established, BFD has two operating modes—active and passive.

· Active mode—BFD actively sends BFD control packets regardless of whether any BFD control packet is received from the peer.

· Passive mode—BFD does not send control packets until a BFD control packet is received from the peer.

At least one end must operate in active mode for a BFD session to be established.

After a BFD session is established, the two ends can operate in the following BFD operating modes:

· Asynchronous mode—The device periodically sends BFD control packets. The device considers that the session is down if it does not receive any BFD control packets within a specific interval.

· Demand mode—The device periodically sends BFD control packets with the D bit set. If the peer end is operating in Asynchronous mode (default), the peer end stops sending BFD control packets after receiving control packets with the D bit set. In this case, BFD detects only the connectivity from the local end to the peer end. If the peer end does not receive control packets within the detection time, the session is declared to be down. If the peer end is operating in Demand mode, both ends stop sending BFD control packets. The system uses other mechanisms such as Hello mechanism and hardware detection to detect links. The Demand mode can be used to reduce the overhead when a large number of BFD sessions exist.

Supported features

Features	Reference
Static routing IS-IS OSPF RIP BGP IP fast reroute (FRR)	Layer 3—IP Routing Configuration Guide
IPv6 static routing OSPFv3	Layer 3—IP Routing Configuration Guide
PIM	IP Multicast Configuration Guide
Track	"Configuring Track"
Ethernet link aggregation	Layer 2—LAN Switching Configuration Guide

Protocols and standards

· RFC 5880, Bidirectional Forwarding Detection (BFD)

· RFC 5881, Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)

· RFC 5882, Generic Application of Bidirectional Forwarding Detection (BFD)

· RFC 5883, Bidirectional Forwarding Detection (BFD) for Multihop Paths

· RFC 7130, Bidirectional Forwarding Detection (BFD) on Link Aggregation Group (LAG) Interfaces

Restrictions and guidelines: BFD configuration

· By default, the device runs BFD version 1 and is compatible with BFD version 0. You cannot change the BFD version to 0 through commands. When the peer device runs BFD version 0, the local device automatically switches to BFD version 0.

· After a BFD session is established, the two ends negotiate BFD parameters, including minimum sending interval, minimum receiving interval, initialization mode, and packet authentication, by exchanging negotiation packets. They use the negotiated parameters without affecting the session status.

· BFD session flapping might occur on an aggregate interface with member ports on different IRF member devices. When the master device, which receives and sends BFD packets, is removed or restarted, a subordinate device might not immediately take over. For example, a subordinate device will not take over when the subordinate device has a short detection time or a large number of BFD sessions.

Configuring BFD sessions in echo packet mode

About BFD session creation methods

A BFD session can be created manually by using the bfd static command or created dynamically through collaboration between an application module and BFD.

Creating a static BFD session

About this task

A static BFD session in echo packet mode can be used to perform single-hop detection or multihop detection.

Restrictions and guidelines

You need to create a static BFD session in echo packet mode on only the local device to perform detection.

When creating a static BFD session, you must specify a peer IPv4 or IPv6 address. The system checks only the format of the IP address but not its correctness. If the peer IPv4 or IPv6 address is incorrect, the static BFD session cannot be established.

Different static BFD sessions cannot have the same local discriminator.

As a best practice, specify the source IP address for echo packets when creating a static BFD session. If you do not specify the source IP address, the device uses the IP address specified in the bfd echo-source-ip or bfd echo-source-ipv6 command as the source IP address of echo packets.

Creating a static BFD session for single-hop detection

1. Enter system view.

system-view

2. Configure the source IP address of echo packets.

¡ Configure the source IP address of echo packets.

bfd echo-source-ip ip-address

By default, no source IPv4 address is configured for echo packets.

As a best practice, do not configure the source IPv4 address to be on the same network segment as any local interfaces. This can avoid network congestion caused a large number of ICMP redirect packets sent from the peer.

¡ Configure the source IPv6 address of echo packets.

bfd echo-source-ipv6 ipv6-address

By default, no source IPv6 address is configured for echo packets.

The source IPv6 address of echo packets can only be a global unicast address.

3. Create a static BFD session and enter static BFD session view.

IPv4:

bfd static session-name [ peer-ip ipv4-address [ vpn-instance vpn-instance-name ] destination-ip ipv4-address [ source-ip ipv4-address ] one-arm-echo[ discriminator { auto | local local-value } ] ]

IPv6:

bfd static session-name [ peer-ipv6 ipv6-address [ vpn-instance vpn-instance-name ] destination-ipv6 ipv6-address [ source-ipv6 ipv6-address ] one-arm-echo [ discriminator { auto | local local-value } ] ]

4. (Optional.) Specify a local discriminator for the static BFD session.

discriminator local local-value

By default, no local discriminator is specified.

You can use this command only if you do not specify a local discriminator when creating a static BFD session.

Creating a static BFD session for multihop detection

1. Enter system view.

system-view

2. (Optional.) Configure the source IP address of echo packets.

¡ Configure the source IPv4 address of echo packets.

bfd echo-source-ip ip-address

By default, no source IPv4 address is configured for echo packets.

As a best practice, do not configure the source IPv4 address to be on the same network segment as any local interfaces. If you configure such a source IPv4 address, a large number of ICMP redirect packets might be sent from the peer, resulting in link congestion.

¡ Configure the source IPv6 address of echo packets.

bfd echo-source-ipv6 ipv6-address

By default, no source IPv6 address is configured for echo packets.

The source IPv6 address of echo packets can only be a global unicast address.

3. Create a static BFD session and enter static BFD session view.

IPv4:

bfd static session-name [ peer-ip ipv4-address interface interface-type interface-number destination-ip ipv4-address [ source-ip ipv4-address ] one-arm-echo [ discriminator { auto | local local-value } ] ]

IPv6:

bfd static session-name [ peer-ipv6 ipv6-address interface interface-type interface-number destination-ipv6 ipv6-address [ source-ipv6 ipv6-address ] one-arm-echo [ discriminator { auto | local local-value } ] ]

4. (Optional.) Specify a local discriminator for the static BFD session.

discriminator local local-value

By default, no local discriminator is specified.

You can use this command only if you do not specify a local discriminator when creating a static BFD session.

Configuring BFD session parameters for single-hop detection

1. Enter system view.

system-view

2. Enter interface view or static BFD session view.

¡ Enter interface view.

interface interface-type interface-number

¡ Enter static BFD session view.

bfd static session-name

The static BFD session must already exist.

To configure parameters for a static BFD session, you must enter its view.

3. Set the minimum interval for receiving BFD echo packets.

bfd min-echo-receive-interval interval

The default setting is 400 milliseconds.

4. Set the detection time multiplier.

bfd detect-multiplier value

The default setting is 5.

Configuring BFD session parameters for multihop detection

1. Enter system view.

system-view

2. (Optional.) Enter static BFD session view.

bfd static session-name

The static BFD session must already exist.

To configure parameters for a static BFD session, you must enter its view.

3. Set the minimum interval for receiving BFD echo packets.

bfd multi-hop min-echo-receive-interval interval

The default setting is 400 milliseconds.

4. Set the detection time multiplier.

bfd multi-hop detect-multiplier value

The default setting is 5.

Configuring BFD sessions in control packet mode

About BFD session creation methods

BFD sessions in control packet mode can be created statically or established dynamically.

BFD sessions are distinguished by the local discriminator and remote discriminator in control packets. The main difference between a statically created session and a dynamically established session is that they obtain the local discriminator and remote discriminator in different ways.

· The local discriminator and remote discriminator of a static BFD session are specified manually in the bfd static command or in the commands that associate specific applications with BFD.

· The local discriminator of a dynamic BFD session is assigned by the device, and the remote discriminator is obtained during BFD session negotiation. The device can automatically assign the local discriminator to the BFD session in the following conditions:

¡ The auto keyword is specified for the bfd static command.

¡ The local and remote discriminators are not specified for the BFD session associated with a specific application.

Restrictions and guidelines

After an upper-layer protocol is configured to support BFD, the device automatically creates BFD sessions in control packet mode. You do not need to perform this task.

Configuring a static BFD session

About this task

A static BFD session can be used for single-hop detection and multihop detection. By working with Track, a static BFD session can provide fast failure detection. For more information about Track association with BFD, see "Configuring Track."

Restrictions and guidelines for static BFD session configuration

If a static BFD session is created on the remote end, the static BFD session must be created on the local end.

Different static BFD sessions cannot have the same local discriminator.

Creating a static BFD session for single-hop detection

1. Enter system view.

system-view

2. Create a static BFD session and enter static BFD session view.

IPv4:

bfd static session-name peer-ip ipv4-address interface interface-type interface-number source-ip ipv4-address [ discriminator { auto | local local-value remote remote-value } ]

For a static BFD session to be established, specify the IPv4 address of the peer interface where the static BFD session resides for the peer-ip ipv4-address option. Specify the IPv4 address of the local interface where the static BFD session resides for the source-ip ipv4-address option.

IPv6:

bfd static session-name peer-ipv6 ipv6-address interface interface-type interface-number source-ipv6 ipv6-address [ discriminator { auto | local local-value remote remote-value } ]

For a static BFD session to be established, specify the IPv6 address of the peer interface where the static BFD session resides for the peer-ipv6 ipv6-address option. Specify the IPv6 address of the local interface where the static BFD session resides for the source-ipv6 ipv6-address option.

3. (Optional.) Specify the local and remote discriminators for the static BFD session.

discriminator { local local-value | remote remote-value }

By default, no local discriminator or remote discriminator is specified for a static BFD session.

Use this command only if you do not specify the local or remote discriminator when creating a static BFD session.

Create a static BFD session for multihop detection

4. Enter system view.

system-view

5. Create a static BFD session and enter static BFD session view.

IPv4:

bfd static session-name peer-ip ipv4-address [ vpn-instance vpn-instance-name ] source-ip ipv4-address [ discriminator { auto |local local-value remote remote-value } ] [ track-interface interface-type interface-number ]

IPv6:

bfd static session-name peer-ipv6 ipv6-address [ vpn-instance vpn-instance-name ] source-ipv6 ipv6-address [ discriminator { auto | local local-value remote remote-value } ] [ track-interface interface-type interface-number ]

6. (Optional.) Specify the local and remote discriminators for the static BFD session.

discriminator { local local-value | remote remote-value }

By default, no local discriminator or remote discriminator is specified for a static BFD session.

Use this command only if you do not specify the local or remote discriminator when creating a static BFD session.

Configuring BFD session parameters for single-hop detection

1. Enter system view.

system-view

2. Enter interface view or static BFD session view.

¡ Enter interface view.

interface interface-type interface-number

¡ Enter static BFD session view.

bfd static session-name

The static BFD session must already exist.

3. Set the minimum interval for receiving echo packets.

bfd min-echo-receive-interval interval

The default setting is 400 milliseconds.

4. Set the minimum interval for transmitting and receiving single-hop BFD control packets.

bfd min-control-interval interval

The default setting is 400 milliseconds.

5. Set the single-hop detection time multiplier.

bfd detect-multiplier value

The default setting is 5.

6. (Optional.) Set the delay timer for BFD to notify upper-layer protocols of session establishment failures.

a. Return to system view.

quit

b. Set the delay timer for BFD to notify upper-layer protocols of session establishment failures.

bfd init-fail-timer seconds

By default, BFD does not notify upper-layer protocols of session establishment failures.

‌

CAUTION:

For session establishment failures caused by configuration mismatches at the two ends, this command can cause the upper-layer protocol to act incorrectly. Therefore, use this command with caution. BFD status mismatch and BFD authentication configuration mismatch are examples of configuration mismatches.

‌

Configuring BFD session parameters for multihop detection

1. Enter system view.

system-view

2. (Optional.) Enter static BFD session view.

bfd static session-name

The static BFD session must already exist.

3. Set the multihop detection time multiplier.

bfd multi-hop detect-multiplier value

The default setting is 5.

4. Set the minimum interval for transmitting and receiving multihop BFD control packets.

bfd multi-hop min-control-interval interval

By default, the minimum interval for transmitting and receiving multihop BFD control packets is 400 milliseconds.

5. (Optional.) Set the delay timer for BFD to notify upper-layer protocols of session establishment failures.

bfd init-fail-timer seconds

By default, BFD does not notify upper-layer protocols of session establishment failures.

This command is supported only in system view.

CAUTION:

Configuring the TTL value for BFD packets

About this task

When you connect an H3C device to a third-party device, for successful BFD session negotiation, make sure the TTL value settings for BFD packets on both ends of the BFD session are the same. When the device receives a BFD packet in DOWN or INIT state from its peer, it verifies the TTL value of the packet and performs one of the following actions:

· For a single-hop BFD session, if the device receives a packet that carries a TTL value that is different from the TTL value specified with the bfd ttl command, the device drops the packet.

· For a multihop BFD session, if the device receives a packet that carries a TTL value that is greater than the TTL value specified with the bfd ttl command, the device drops the packet.

· If the BFD session is already up, the device sets the BFD session state to AdminDown, which triggers a BFD session renegotiation.

Restrictions and guidelines

· The bfd ttl command does not take effect on BFD sessions in echo packet mode.

· The bfd ttl command does not take effect on SBFD packets,and the device does not verify the TTL value in SBFD packets.

· For an IPv4 or IPv6 addresswith different mask lengths or prefix lengths, the device uses the TTL value specified with the longest mask or prefix length.

· For an IPv4 or IPv6 subnet, the TTL value of single-hop BFD packets must be greater than the TTL value of multihop BFD packets.

Procedure

1. Enter system view.

system-view

2. Specify the TTL value for BFD packets.

bfd { peer-ip ipv4-address mask-length | peer-ipv6 ipv6-address prefix-length } ttl { single-hop | multi-hop } ttl-value

By default, the TTL value of single-hop BFD packets is 255 and the TTL value of multihop BFD packets is 64.

Configuring a BFD template

About this task

Perform this task to specify BFD parameters in a template for sessions without next hops. You can configure BFD parameters for LSPs and PWs through a BFD template.

This task can also be used to specify BFD parameters for BFD sessions that detect interface states.

Procedure

1. Enter system view.

system-view

2. Set the detection time multiplier.

bfd detect-multiplier value

The default setting is 5.

3. Set the minimum interval for transmitting and receiving BFD control packets.

bfd min-control-interval interval

The default setting is 400 milliseconds.

Enabling SNMP notifications for BFD

About this task

To report critical BFD events to an NMS, enable SNMP notifications for BFD. For BFD event notifications to be sent correctly, you must also configure SNMP as described in Network Management and Monitoring Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enable SNMP notifications for BFD.

snmp-agent trap enable bfd

By default, SNMP notifications are enabled for BFD.

Display and maintenance commands for BFD

Execute the display command in any view and the reset command in user view.

Task	Command
Display BFD session information.	display bfd session [ discriminator local local-value \| static session-name \| verbose ] display bfd session [ [ dynamic ] [ control \| echo ] [ ip ] [ state { down \| admin-down \| init \| up } ] [ discriminator remote remote-value ] [ peer-ip ipv4-address [ vpn-instance vpn-instance-name ] ] [ verbose ] ] display bfd session [ [ dynamic ] [ control \| echo ] [ ipv6 ] [ state { down \| admin-down \| init \| up } ] [ discriminator remote remote-value ] [ peer-ipv6 ipv6-address [ vpn-instance vpn-instance-name ] ] [ verbose ] ] display bfd session [ [ static ] [ ip ] [ state { down \| admin-down \| init \| up } ] [ discriminator remote remote-value ] [ peer-ip ipv4-address [ vpn-instance vpn-instance-name ] ] [ verbose ] display bfd session [ [ static ] [ ipv6 ] [ state { down \| admin-down \| init \| up } ] [ discriminator remote remote-value ] [ peer-ipv6 ipv6-address [ vpn-instance vpn-instance-name ] ] [ verbose ]
Display the TTL values for BFD packets.	display bfd ttl
Clear BFD session statistics.	reset bfd session statistics

10-High Availability Configuration Guide

Echo packet mode

Control packet mode

Configuring BFD sessions in echo packet mode

About BFD session creation methods

About this task

Restrictions and guidelines

Creating a static BFD session for single-hop detection

Creating a static BFD session for multihop detection

About this task

Restrictions and guidelines for static BFD session configuration

Creating a static BFD session for single-hop detection

Create a static BFD session for multihop detection

Configuring the TTL value for BFD packets

About this task

Restrictions and guidelines

Procedure

About this task

Procedure

Enabling SNMP notifications for BFD

About this task

Procedure

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