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· 3

Configuring BFD sessions in echo packet mode· 3

Configuring BFD sessions in control packet mode· 4

About BFD session creation methods· 4

Restrictions and guidelines· 4

Configuring a static BFD session· 4

Configuring BFD session parameters for single-hop detection· 5

Configuring BFD session parameters for multihop detection· 6

Enabling the echo function· 7

Associating the interface state with BFD·· 7

Configuring BFD session flapping suppression· 8

Configuring a BFD template· 9

Enabling SNMP notifications for BFD·· 9

Display and maintenance commands for BFD·· 9

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 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 multihop detection only for MPLS TE tunnel scenarios. Both BFD sessions for single-hop detection and BFD sessions for multihop detection 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. After a BFD session is established, both ends send BFD control packets to each other at the negotiated intervals by default.

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 IPv6 PIM	IP Multicast Configuration Guide
RSVP MPLS L3VPN MPLS OAM	MPLS 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 5884, Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)

·          RFC 5885, Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV)

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

Restrictions and guidelines: BFD configuration

·          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.

·          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.

·          If hardware BFD is enabled, you can configure a maximum of six different minimum receiving interval values for all BFD sessions on the device.

·          In a network where Layer 2 relay devices exist between IRF member devices, make sure the following values are greater than four times the IRF link detection interval:

¡  Minimum interval for receiving BFD echo packets.

¡  Minimum interval for transmitting or receiving single-hop BFD control packets.

¡  Minimum interval for transmitting or receiving multihop BFD control packets.

The IRF link detection interval is set by using the irf link-detect-time command. For more information about the command, see IRF in Virtual Technologies Configuration Guide.

Configuring BFD sessions in echo packet mode

Restrictions and guidelines

To avoid echo packet loss, do not configure the echo packet mode on a device with uRPF enabled. For more information about uRPF, see Security Configuration Guide.

Procedure

1.        Enter system view.

system-view

2.        (Optional.) Enable hardware BFD.

hardware bfd enable [ high-precision ]

By default, hardware BFD and high-precision hardware BFD are disabled.

3.        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 interface's IPv4 address. 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.

4.        (Optional.) Set the echo packet mode parameters.

a.    Enter interface view.

interface interface-type interface-number

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

bfd min-echo-receive-interval interval

The default setting is 400 milliseconds.

c.    Set the detection time multiplier.

bfd 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 features associated 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. A created session without manually specified local and remote discriminators is a dynamic BFD session.

Restrictions and guidelines

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 configuring a static BFD session

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.        (Optional.) Enable hardware BFD.

hardware bfd enable [ high-precision ]

By default, hardware BFD and high-precision hardware BFD are disabled.

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 source-ip ipv4-address discriminator local local-value remote remote-value

Specify the IPv4 addresses of the peer interface and local interface where the static BFD session resides for the peer-ip ipv4-address and source-ip ipv4-address options, respectively. Without the settings, the static BFD session cannot be established.

IPv6:

bfd static session-name peer-ipv6 ipv6-address interface interface-type interface-number source-ipv6 ipv6-address discriminator local local-value remote remote-value

Specify the IPv6 addresses of the peer interface and local interface where the static BFD session resides for the peer-ipv6 ipv6-address and source-ipv6 ipv6-address options, respectively. Without the settings, the static BFD session cannot be established.

Create a static BFD session for multihop detection

1.        Enter system view.

system-view

2.        (Optional.) Enable hardware BFD.

hardware bfd enable [ high-precision ]

By default, hardware BFD and high-precision hardware BFD are disabled.

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 ] source-ip ipv4-address discriminator local local-value remote remote-value

IPv6:

bfd static session-name peer-ipv6 ipv6-address [ vpn-instance vpn-instance-name ] source-ipv6 ipv6-address discriminator local local-value remote remote-value

Configuring BFD session parameters for single-hop detection

1.        Enter system view.

system-view

2.        Specify the mode for establishing a BFD session.

bfd session init-mode { active | passive }

By default, active is specified.

3.        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.

4.        Configure the authentication mode for single-hop control packets.

bfd authentication-mode { m-md5 | m-sha1 | md5 | sha1 | simple } key-id { cipher cipher-string | plain plain-string }

By default, single-hop BFD packets are not authenticated.

5.        Enable the Demand BFD session mode.

bfd demand enable

By default, the BFD session is in Asynchronous mode.

This command is supported only in interface view.

6.        Set the minimum interval for transmitting single-hop BFD control packets.

bfd min-transmit-interval interval

The default setting is 400 milliseconds.

7.        Set the minimum interval for receiving single-hop BFD control packets.

bfd min-receive-interval interval

The default setting is 400 milliseconds.

8.        Set the single-hop 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.

3.        Specify the mode for establishing a BFD session.

bfd session init-mode { active | passive }

By default, active is specified.

This command is supported only in system view.

4.        Configure the authentication mode for multihop BFD control packets.

bfd multi-hop authentication-mode { m-md5 | m-sha1 | md5 | sha1 | simple } key-id { cipher cipher-string | plain plain-string }

By default, no authentication is performed.

5.        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.

6.        Set the multihop detection time multiplier.

bfd multi-hop detect-multiplier value

The default setting is 5.

7.        Set the minimum interval for receiving multihop BFD control packets.

bfd multi-hop min-receive-interval interval

The default setting is 400 milliseconds.

8.        Set the minimum interval for transmitting multihop BFD control packets.

bfd multi-hop min-transmit-interval interval

The default setting is 400 milliseconds.

Enabling the echo function

About the echo function

This function enables the local system to periodically send echo packets to the remote system. The remote system loops back the echo packets to the local system without processing them. If the local system does not receive the looped-back echo packets, it declares the BFD session down.

This function is supported only for single-hop detection.

Restrictions and guidelines

If you configure both the bfd detect-interface and bfd echo enable commands on the same interface, only the bfd detect-interface command takes effect.

Procedure

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.        Enable the echo function.

bfd echo [ receive | send ] enable

By default, the echo function is disabled.

Associating the interface state with BFD

About associating the interface state with BFD

By creating a BFD session for single-hop detection through exchange of BFD control packets, this feature implements fast link detection. When BFD detects a link fault, it sets the link layer protocol state to DOWN(BFD). This behavior helps applications relying on the link layer protocol state achieve fast convergence. The source IP address of control packets is specified manually, and the destination IP address is fixed at 224.0.0.184. As a best practice, specify the IP address of the interface as the source IP address. If the interface does not have an IP address, specify a unicast IP address other than 0.0.0.0 as the source IP address.

You can associate the state of the following interfaces with BFD:

·          Layer 2 Ethernet interfaces.

·          Member ports in a Layer 2 aggregation group.

·          Layer 3 Ethernet interfaces.

·          Member ports in a Layer 3 aggregation group.

Restrictions and guidelines

The echo function does not take effect on BFD sessions associated with interface states.

Procedure

1.        Enter system view.

system-view

2.        Enter interface view.

interface interface-type interface-number

3.        Associate the interface state with BFD.

bfd detect-interface source-ip ip-address [ discriminator local local-value remote remote-value ]

If the peer device does not support obtaining BFD session discriminators through autonegotiation, you must specify the discriminators on both the local and peer devices. Without the discriminators, the BFD session cannot come up.

Configuring BFD session flapping suppression

About BFD session flapping suppression

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 value for the initial-interval or secondary-interval argument cannot be greater than the value for the maximum-interval argument.

Configuring a BFD template

About configuring a BFD template

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.

Procedure

1.        Enter system view.

system-view

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

bfd template template-name

3.        (Optional.) Configure the authentication mode for BFD control packets.

bfd authentication-mode { m-md5 | m-sha1 | md5 | sha1 | simple } key-id { cipher cipher-string | plain plain-string }

By default, no authentication is performed.

4.        Set the detection time multiplier.

bfd detect-multiplier value

The default setting is 5.

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

bfd min-echo-receive-interval interval

The default setting is 400 milliseconds.

6.        Set the minimum interval for receiving BFD control packets.

bfd min-receive-interval interval

The default setting is 400 milliseconds.

7.        Set the minimum interval for transmitting BFD control packets.

bfd min-transmit-interval interval

The default setting is 400 milliseconds.

Enabling SNMP notifications for BFD

About SNMP notifications for BFD

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 value | verbose ]
Display the BFD hardware mode and hardware resource usage.	display bfd system mode info
Clear BFD session statistics.	reset bfd session statistics