Contents

Configuring BFD·· 1

About BFD·· 1

Single-hop detection and multihop detection· 1

BFD session modes· 1

Supported features· 2

Protocols and standards· 2

Restrictions and guidelines: BFD configuration· 2

Configuring BFD sessions in control packet mode· 2

About BFD session creation methods· 2

Restrictions and guidelines· 3

Configuring a static BFD session· 3

Configuring BFD session parameters for single-hop detection· 4

Configuring BFD session parameters for multihop detection· 5

Configuring the TTL value for BFD packets· 6

Configuring BFD session flapping suppression· 6

Configuring a BFD template· 7

Enabling SNMP notifications for BFD·· 7

Display and maintenance commands for BFD·· 8

Configuring BFD

About BFD

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 control packets.

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 cards. When the card that receives and sends BFD packets is removed or restarted, the backup card might not immediately take over. For example, the backup card will not take over when the card has a short detection time or a large number of BFD sessions. (In IRF mode.)

·     An LSCM1GT48SC0 card does not support IPv6 BFD sessions.

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.

BFD version 0 does not support the following commands:

·     bfd session init-mode.

·     bfd authentication-mode.

·     bfd demand enable.

·     bfd echo enable.

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.

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.

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

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 [ 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 ]

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.

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.

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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.     Configure the destination port number for multihop BFD control packets.

bfd multi-hop destination-port port-number

The default setting is 4784.

This command is supported only in system view.

4.     Set the multihop detection time multiplier.

bfd multi-hop detect-multiplier value

The default setting is 5.

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

bfd multi-hop min-control-interval interval

The default setting is 400 milliseconds.

6.     (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: 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 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 BFD session flapping suppression

About this task

When BFD detects a link failure, it tears down the BFD session and notifies the upper-layer protocol of the failure. When the upper-layer protocol re-establishes a neighbor relationship, the BFD session comes up again. BFD session flaps occur when a link fails and recovers repeatedly, which consumes significant system resources and causes network instability.

This feature allows you to suppress BFD session flapping by using the initial-interval, secondary-interval, and maximum-interval arguments.

·     A BFD session is suppressed within the specified interval. The suppression time does not exceed the maximum-interval.

·     After a BFD session goes down for the second time, it cannot be re-established within the initial-interval.

·     After a BFD session goes down for the third time, it cannot be re-established within the secondary-interval.

·     After a BFD session goes down for the fourth time and at any later time, the following rules apply:

¡     If secondary-interval × 2n-3 is smaller than or equal to the maximum-interval, the BFD session cannot be re-established within the secondary-interval × 2n-3.

¡     If secondary-interval × 2n-3 is greater than the maximum-interval, the BFD session cannot be re-established within the maximum-interval.

The letter n, starting from 4, is the number of times the BFD session flaps.

Procedure

1.     Enter system view.

system-view

2.     Configure BFD session flapping suppression.

bfd dampening [ maximum maximum-interval initial initial-interval secondary secondary-interval ]

By default, BFD sessions are not suppressed.

The values for the initial-interval and secondary-interval arguments cannot be greater than the value for the maximum-interval argument.

Configuring a BFD template

About this task

Perform this task to specify BFD parameters in a template for sessions without next hops.

Procedure

1.     Enter system view.

system-view

2.     Create a BFD template and enter BFD template view.

bfd template template-name

3.     Set the detection time multiplier.

bfd detect-multiplier value

The default setting is 5.

4.     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 [ [ dynamic ] [ control | echo ] [ lsp | te | pw ] [ state { down | admin-down | init | up } ] [ discriminator remote remote-value ] [ [ peer-ip ipv4-address [ vpn-instance vpn-instance-name ] ] | [ 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