Configuring Bidirectional Forwarding Detection

Bidirectional Forwarding Detection

Bidirectional Forwarding Detection (BFD) is a protocol designed to quickly identify faults in the forwarding path between two devices. BFD simplifies network profiling and planning by offering predictable reconvergence time.

BFD detects forwarding path failures across various media types, encapsulations, topologies, and routing protocols. It provides subsecond failure detection between two adjacent devices, distributing some load onto the data plane on supported modules. BFD can be less CPU-intensive than protocol hello messages.

Asynchronous mode

BFD asynchronous mode is a BFD session mode that:

  • involves the exchange of periodic control packets to monitor connectivity,

  • establishes and maintains BFD neighbor sessions, and

  • negotiates session parameters.

BFD session parameters

The table lists the BFD session parameters and the intervals.

Table 1. BFD session parameters
Session Parameters Description
Desired minimum transmit interval The interval at which the device is configured to send BFD hello messages.
Required minimum receive interval The minimum interval at which the device can accept BFD hello messages from another BFD device.
Detect multiplier The number of missing BFD hello messages required to detects a fault in the forwarding path.

BFD neighbor workflow

The figure details the BFD neighbor sessions establishment between two routers.

Figure 1. Establishing a BFD Neighbor Relationship


The stages that establish a BFD neighbor session are:

  1. The OSPF process discovers a BFD neighbor.

  2. The local BFD process gets a request to start a session BFD neighbor session with the OSPF neighbor router.

  3. The session is established between the BFD neighbor with the OSPF neighbor router.

BFD Detection of Failures

Once a BFD session has been established and timer negotiations are complete, BFD neighbors send BFD control packets that act in the same manner as an IGP hello protocol to detect liveliness, except at a more accelerated rate. BFD detects a failure, but the protocol must take action to bypass a failed peer.

BFD sends a failure detection notice to the BFD-enabled protocols when it detects a failure in the forwarding path. The local device can then initiate the protocol recalculation process and reduce the overall network convergence time.

The following figure shows what happens when a failure occurs in the network (1). The BFD neighbor session with the OSPF neighbor router is torn down (2). BFD notifies the local OSPF process that the BFD neighbor is no longer reachable (3). The local OSPF process tears down the OSPF neighbor relationship (4). If an alternative path is available, the routers immediately start converging on it.


Note

Note The BFD failure detection occurs in less than a second, which is much faster than OSPF Hello messages could detect the same failure.

Figure 2. Tearing Down an OSPF Neighbor Relationship


Distributed Operation

Cisco NX-OS can distribute the BFD operation to compatible modules that support BFD. This process offloads the CPU load for BFD packet processing to the individual modules that connect to the BFD neighbors. All BFD session traffic occurs on the module CPU. The module informs the supervisor when a BFD failure is detected.

BFD Echo Function

Echo packets are defined and processed only by the transmitting system. For IPv4 and IPv6, the echo packets' destination address is that of the transmitting device. It is chosen in such a way as to cause the remote system to forward the packet back to the local system. This bypasses the routing lookup on the remote system and relies on the forwarding information base (FIB) instead. BFD can use the slow timer to slow down the asynchronous session when the echo function is enabled and reduce the number of BFD control packets that are sent between two BFD neighbors. The Echo function tests only the forwarding path of the remote system by having the remote (neighbor) system loop them back, so there is less inter-packet delay variability and faster failure detection times.

Security

Cisco NX-OS uses the packet Time to Live (TTL) value to verify that the BFD packets came from an adjacent BFD peer. For all asynchronous and echo request packets, the BFD neighbor sets the TTL value to 255 and the local BFD process verifies the TTL value as 255 before processing the incoming packet. For the echo response packet, BFD sets the TTL value to 254.

You can configure SHA-1 authentication of BFD packets.

High Availability

BFD supports stateless restarts. After a reboot or supervisor switchover, Cisco NX-OS applies the running configuration and BFD immediately sends control packets to the BFD peers.

Virtualization Support

BFD supports virtual routing and forwarding instances (VRFs). VRFs exist within virtual device contexts (VDCs). By default, Cisco NX-OS places you in the default VDC and default VRF.

Prerequisites for BFD

Ensure you meet these prerequisites before you configure BFD.

  • Enable the BFD feature.

  • Disable ICMP redirect messages on interfaces where BFD is enabled.

  • Disable the IP packet verification check for identical IP source and destination addresses.

  • Review the detailed prerequisites in the configuration tasks.

Guidelines and Limitations

BFD has the following configuration guidelines and limitations:

  • The QSFP 40/100-G BiDi comes up in the highest possible speed available on the port. For example, in the Cisco Nexus 93180LC-EX switch it comes up as 40 G in the first 28 ports and 100 G in the last 4 ports. If you need to connect to 40-G SR4 BiDi, the speed on the 40/100-G BiDi needs to be set to 40 G.

  • BFD over private-vlan is not supported Cisco Nexus 9000 Switches.

  • Beginning with Cisco NX-OS Release 10.2(1q)F, Layer 3 Unicast BFD is supported on Cisco Nexus N9K-C9332D-GX2B platform switches.

  • Forming BFD neighbors on a vPC VLAN through an orphan port is not supported on Cisco Nexus 9000 Switches.

  • Beginning with Cisco NX-OS Release 9.2(1), QSFP-40/100-SRBD comes up in the speed of 100-G and inter-operate with other QSFP-40/100-SRBD at either 40-G or 100-G speed on Cisco Nexus 9500 Switches with the N9K-X9636C-RX line card. The QSFP-40/100-SRBD can also inter-operate with QSFP-40G-SR-BD at 40G speeds. However to operate at 40G speed, you must configure the speed as 40G.

  • show commands with the internal keyword are not supported.

  • BFD per-member link support is added on Cisco Nexus 9000 Series switches.

  • BFD supports BFD version 1.

  • BFD supports IPv4 and IPv6.

  • BFD supports OSPFv3.

  • BFD supports IS-ISv6.

  • When configuring BFD over IP unnumbered interfaces, use these guidelines:

    • Disable the BFD echo function to prevent the interface from flapping.

    • Enable BFD multihop when configuring BGP over IP unnumbered interface.

  • Set the ipv6 nd ns-interval command range to 15 under the Layer 3 interface configuration to prevent BFD sessions from flapping, when there are a large number of IPv6 adjacencies.

    Alternatively, increase the BFD echo interval to avoid session instability that might occur due to CoPP drops of NS/NA packets.

  • BFD supports BGPv6.

  • BFD supports EIGRPv6.

  • BFD supports only sessions which have unique (src_ip, dst_ip, interface/vrf) combination.

  • BFD supports single-hop BFD.

    • Only single-hop static BFD is supported.

    • BFD for BGP supports single-hop EBGP and iBGP peers.

  • BFD supports keyed SHA-1 authentication.

  • BFD supports the following Layer 3 interfaces—physical interfaces, port channels, sub-interfaces, and VLAN interfaces.

  • BFD depends on a Layer 3 adjacency information to discover topology changes, including Layer 2 topology changes. A BFD session on a VLAN interface (SVI) may not be up after the convergence of the Layer 2 topology if there is no Layer 3 adjacency information available.

  • For BFD on a static route between two devices, both devices must support BFD. If one or both of the devices do not support BFD, the static routes are not programmed in the Routing Information Base (RIB).

  • Both single-hop and multi-hop BFD features are supported with specific restrictions. For multi-hop BFD features restrictions, refer to Guidelines and Limitations for BFD Multihop section.

  • Port channel configuration limitations:

    • For Layer 3 port channels used by BFD, you must enable LACP on the port channel.

    • For Layer 2 port channels used by SVI sessions, you must enable LACP on the port channel.

  • SVI limitations:

    • An ASIC reset causes traffic disruption for other ports and it can cause the SVI sessions on the other ports to flap. For example, if the carrier interface is a virtual port channel (vPC), BFD is not supported over the SVI interface and it could cause a trigger for an ASIC reset. When a BFD session is over SVI using virtual port channel (vPC) Peer-Link, the BFD echo function is not supported. You must disable the BFD echo function for all sessions over SVI between vPC peer nodes.

      An SVI on the Cisco Nexus series switches should not be configured to establish a BFD neighbor adjacency with a device connected to it via a vPC. This is because the BFD keepalives from the neighbor, if sent over the vPC member link connected to the vPC peer-switch, do not reach this SVI causing the BFD adjacency to fail.

    • When you change the topology (for example, add or delete a link into a VLAN, delete a member from a Layer 2 port channel, and so on), the SVI session could be affected. It may go down first and then come up after the topology discovery is finished.

    • BFD over FEX HIF interfaces is not supported.

    • When a BFD session is over SVI using virtual port-channel (vPC) Peer-Link (either BCM or GEM based ports), the BFD echo function is not supported. You must disable the BFD echo function for all sessions over SVI between vPC peer nodes using the no bfd echo command at the SVI configuration level.


      Tip

      If you do not want the SVI sessions to flap and you need to change the topology, you can disable the BFD feature before making the changes and re-enable BFD after the changes have been made. You can also configure the BFD timer to be a large value (for example, 5 seconds), and change it back to a fast timer after the above events complete.

  • When you configure the BFD Echo function on the distributed Layer 3 port channels, reloading a member module flaps the BFD session hosted on that module, which results in a packet loss.

    If you connect the BFD peers directly without a Layer 2 switch in between, you can use the BFD per-link mode as an alternative solution.


    Note

    Using BFD per-link mode and sub-interface optimization simultaneously on a Layer 3 port channel is not supported.

  • When you specify a BFD neighbor prefix in the clear {ip | ipv6} route prefix command, the BFD echo session flaps.

  • The clear {ip | ipv6} route * command causes BFD echo sessions to flap.

  • HSRP for IPv4 is supported with BFD.

  • BFD packets generated by the Cisco NX-OS device line cards are sent with COS 6/DSCP CS6. The DSCP/COS values for BFD packets are not user configurable.

  • When configuring BFDv6 in no-bfd-echo mode, it is recommended to run with timers of 150 ms with a multiplier of 3.

  • BFDv6 is not supported for VRRPv3 and HSRP for v6.

  • IPv6 eigrp bfd cannot be disabled on an interface.

  • IETF BFD is not supported on N9K-X96136YC-R, N9K-X9636C-R, N9K-X9636C-RX and N9K-X9636Q-R line cards.

  • Port channel configuration notes:

    • When the BFD per-link mode is configured, the BFD echo function is not supported. You must disable the BFD echo function using the no bfd echo command before configuring the bfd per-link command.

    • Before configuring BFD per-link, make sure there is no BFD session running on the port-channel. If there is any BFD session running already, remove it and then proceed with bfd per-link configuration.

    • Configuring BFD per-link with link-local is not supported.

    • The supported platforms include Cisco Nexus 9500 Series switches with N9K-X9636C-R, N9K-X9636Q-R, N9K-X9636C-RX line cards.

  • Beginning with Cisco NX-OS Release 9.3(7), BFD is supported on unnumbered interfaces.


    Note

    BFD over unnumbered Switched Virtual Interfaces (SVIs) are not supported.

    Downgrade compatibility for BFD on unnumbered interface support cannot be verified using show incompatibility nxos bootflash:filename command. The compatibility will be checked during install all command.

  • Beginning with Cisco NX-OS Release 10.5(2)F, BFD over IP unnumbered is not supported on Cisco Nexus 9808 and 9804 switches.

  • When you configure BFD on a numbered interface along with OSPF and when the interface is converted to an unnumbered interface, the OSPF and BFD command remains in the running configuration but the BFD functionality may not work

  • The following BFD command configurations are not supported for configuration replace:

    • port-channel bfd track-member-link

    • port-channel bfd destination destination-ip-address

  • Cisco Nexus 9800 platform switches have the following limitation for BFD IPv6 sessions:

    • Each ASIC unit in supervisor switch mode of line card supports a maximum of 256 BFD IPv6 sessions. If more BFD IPv6 sessions are required, sessions must be spread across ASIC units or line cards.

  • Beginning with Cisco NX-OS Release 10.3(1)F, BFD supports single-hop BFD on routed port, routed-sub interface, and breakout port of Cisco Nexus 9808 platform switches.

  • Beginning with Cisco NX-OS Release 10.4(1)F, BFD supports single-hop BFD on routed port, routed-sub interface, and breakout port of Cisco Nexus 9804 platform switches.

  • Beginning with Cisco NX-OS Release 10.4(2)F the following are applicable for Cisco Nexus C9232E-B1 switch:

    • Single-hop BFD on routed port, routed-sub interface, and breakout ports are supported.

    • BFD Authentication is not supported.

  • Beginning with Cisco NX-OS Release 10.5(3)F, the Cisco Nexus 93C64E-SG2-Q switch supports these features.

    • Single-hop BFD on Layer 3 physical interfaces and physical subinterfaces

    • Single-hop BFD on Layer 3 port channel and port channel subinterfaces

    • Single-hop BFD on routed port and breakout ports

    • Single-hop BFD on IPv4 and IPv6 address

    • Minimum BFD timer with 50ms

    • BFD asynchronous mode

    • BFD echo function

  • Use the bfd authentication interop command to configure BFD authentication interoperability between Nexus and non-Nexus platforms. If you do not configure this command, BFD authentication fails due to an invalid authentication sequence number field format.

  • BFD Authentication is not supported on Cisco Nexus 9800 platform switches.

  • Beginning with Cisco NX-OS Release 10.4(1)F, BFD supports single-hop BFD on N9KX98900CD-A and N9KX9836DM-A line cards with Cisco Nexus 9808 and 9804 switches.

  • Beginning with Cisco NX-OS Release 10.4(3)F, single hop BFD is supported on Cisco Nexus 9808 and 9804 L3 port-channel interfaces and port-channel sub-interfaces with the following limitations:

    • Per Port-channel interface, only 128 sessions are supported.

    • BFD authentication is not supported.

  • Beginning with Cisco NX-OS Release 10.4(3)F, single-hop BFD is supported on Layer 3 port channel on Cisco Nexus 9800 switches. The BFD server selects the hosting line card for the session among the available online line cards. However, this feature has the following limitations:

    • If the hosting line card changes, the ongoing session gets deleted on that line card, and the hosting is created on another line card that is available.

    • If the source IP of the BFD session changes, the ongoing session gets deleted and recreated with the new source IP.

BFD Support on Nexus Switches

BFD support is available on the Nexus platforms in these releases. For more information, see platform support matrix.

Table 2. BFD Support on Nexus Switches

Platform

Introduced in Cisco NX-OS Release

N93-C64E-SG2-Q

10.5.3F

N9K-C9364C-H1

10.4.3F

N9K-C93400LD-H1

N9K-C9232E-B1

10.4.2F

Nexus 9804

N9K-C9332D-H2R

10.4.1F

Nexus 9808

10.3.1F

N9K-C9348D-GX2A

N9K-C9364D-GX2A

N9K-C9332D-GX2B

Cisco Nexus 9300-EX, 9300-FX, 9300-FX2, 9300-FX3, and 9300-GX

10.2.3F

9364C-GX

9316D-GX

93600CD-GX

N9K-X96136YC-R, N9K-X9636C-R, N9K-X9636C-RX and N9K-X9636Q-R

9.3.3F

Default Settings

The following table lists the default settings for BFD parameters.

Table 3. Default BFD Parameters

Parameters

Default

BFD feature

Disabled

Required minimum receive interval

50 milliseconds

Desired minimum transmit interval

50 milliseconds

Detect multiplier

3

Echo function

Enabled

Mode

Asynchronous

Port-channel

Logical mode (one session per source-destination pair address)

Slow timer

2000 milliseconds

Configuring BFD

Best Practices for BFD configuration hierarchy and inheritance

Consider these points when you configure BFD at:

  • Interface-level configuration versus global configuration

  • Member ports and port channels

Interface-level configuration versus global configuration

Configure BFD at both the global level and at the interface level.


Note

Interface-level configuration overrides the global configuration.

Inheritance for member ports and port channels

Configure the member port to inherit the BFD configuration of the primary port channel.

Task Flow for Configuring BFD

Follow these steps in the following sections to configure BFD:

  • Enabling the BFD Feature.

  • Configuring Global BFD Parameters or Configuring BFD on an Interface.

Enable BFD feature

Enable the BFD feature to configure BFD on an interface and protocol.

Procedure

Step 1

Enter the configuration mode with the configure terminal command.

Example:

switch# configure terminal
switch(config)#

Step 2

Enable BFD with the feature bfd command.

Example:

switch(config)# feature bfd

Step 3

(Optional) View the status of features with the show feature | include bfd command.

Example:

switch(config)# show feature | include
bfd

Step 4

(Optional) Save the configuration with the copy running-config startup-config command.

Example:

switch(config)# copy running-config startup-config

Disable BFD

Procedure
Command or Action Purpose

Disable the BFD feature and remove all associated configurations with the no feature bfd command.

Example:
switch(config)# no feature bfd

Configure global BFD parameters

Configure default session behaviors for all BFD (Bidirectional Forwarding Detection) sessions on your device.

BFD global parameters set the timer and detection characteristics for all BFD sessions. You can override these parameters at the interface.

You can configure these settings for all BFD sessions on the device. Both BFD peers negotiate the session parameters in a three-way handshake.

To override these global session parameters on an interface, see Configuring BFD on an Interface.

Use these steps to configure global BFD parameters.

Before you begin

Enable the BFD feature, see Configure global BFD parameters

Procedure

Step 1

Enter configuration mode using the configure terminal command.

Example:

switch# configure terminal 
switch(config)#

Step 2

Configure the BFD session parameters for all BFD sessions using the bfd interval mintx min_rx msec multiplier value command.

Example:

switch(config)# bfd interval 50 min_rx 50 multiplier 3

This command overrides the values you configure for BFD session parameters on individual interfaces.

The intervals mintx and msec range from 50 milliseconds to 999 milliseconds, with a default of 50 milliseconds.

The multiplier ranges from 1 to 50. The default is 3.

Step 3

Configure the slow timer used in the echo function using the bfd slow-timer [interval] command.

Example:

switch(config)# bfd slow-timer 2000

This value determines how quickly BFD starts a new session. It specifies the rate at which asynchronous sessions send BFD control packets when the echo function is enabled.

The slow-timer value sets the interval for control packets. Echo packets use the configured BFD intervals for link failure detection. Control packets at the slower rate maintain the BFD session.

The range is from 1000 to 30,000 milliseconds. The default is 2000.

Step 4

Configure the interface used for Bidirectional Forwarding Detection (BFD) echo frames bfd echo-interface loopback interface number

Example:

switch(config)# bfd echo-interface loopback 1 3

This command changes the source address for the echo packets to the one configured on the specified loopback interface. The interface number range is from 0 to 1023.

Step 5

(Optional) Display the BFD running configuration using the show running-config bfd command.

Example:

switch(config)# show running-config bfd

Step 6

(Optional) Save the configuration using the copy running-config startup-config command.

Example:

switch(config)# copy running-config startup-config

Your device uses the specified default BFD parameters for all BFD sessions unless you override them on an interface.

Example

Configure BFD on an Interface

You can configure the BFD session parameters for all BFD sessions on an interface. The BFD session parameters are negotiated between the BFD peers in a three-way handshake.

This configuration overrides the global session parameters for the configured interface.

Before you begin

Ensure that Internet Control Message Protocol (ICMP) redirect messages are disabled on BFD-enabled interfaces. Use the no ip redirects command or the no ipv6 redirects command on the interface.

Enable the BFD feature. See the Enabling the BFD Feature section.

Procedure

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

interface int-if

Example:

switch(config)# interface ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 3

bfd interval mintx min_rx msec multiplier value

Example:

switch(config-if)# bfd interval 50
min_rx 50 multiplier 3

Configures the BFD session parameters for all BFD sessions on the device. This command overrides these values by configuring the BFD session parameters on an interface. The mintx and msec range is from 50 to 999 milliseconds and the default is 50. The multiplier range is from 1 to 50. The multiplier default is 3.

Beginning with Cisco NX-OS Release 9.3(5), configuring BFD session parameters under interface with default timer values using the bfd interval 50 min_rx 50 multiplier 3 command is functionally equivalent to no bfd interval command.

Once BFD session parameters under interface are set to default values, those BFD sessions running on that interface will inherit global session parameters, if present.

Step 4

bfd authentication keyed-sha1 keyid id key ascii_key

Example:

switch(config-if)# bfd authentication
keyed-sha1 keyid 1 ascii_key cisco123

(Optional) Configures SHA-1 authentication for all BFD sessions on the interface. The ascii_key string is a secret key shared among BFD peers. The id value, a number between 0 and 255, is assigned to this particular ascii_key . BFD packets specify the key by id , allowing the use of multiple active keys.

To disable SHA-1 authentication on the interface, use the no form of the command.

Step 5

Use the bfd authentication interop command to configure BFD authentication interoperability between Nexus and non-Nexus platforms.

Example:

switch(config-if)# bfd authentication interop

Step 6

show running-config bfd

Example:

switch(config-if)# show running-config bfd

(Optional) Displays the BFD running configuration.

Step 7

copy running-config startup-config

Example:

switch(config-if)# copy running-config startup-config

(Optional) Saves the configuration change.

Example

What to do next

Configuring BFD on a Port Channel

You can configure the BFD session parameters for all BFD sessions on a port channel. If per-link mode is used for Layer 3 port channels, BFD creates a session for each link in the port channel and provides an aggregate result to client protocols. For example, if the BFD session for one link on a port channel is up, BFD informs client protocols, such as OSPF, that the port channel is up. The BFD session parameters are negotiated between the BFD peers in a three-way handshake.

This configuration overrides the global session parameters for the configured port channel. The member ports of the port channel inherit the port channel BFD session parameters.

Before you begin

Ensure that you enable LACP on the port channel before you enable BFD.

Ensure that Internet Control Message Protocol (ICMP) redirect messages are disabled on BFD-enabled interfaces. Use the no ip redirects command on the interface.

Enable the BFD feature. See the Enabling the BFD Feature section.

SUMMARY STEPS

  1. configure terminal
  2. interface port-channel number
  3. bfd per-link
  4. bfd interval mintx min_rx msec multiplier value
  5. bfd authentication keyed-sha1 keyid id key ascii_key
  6. show running-config bfd
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface port-channel number

Example:

switch(config)# interface port-channel 2
switch(config-if)#

Enters port-channel configuration mode. Use the ? keyword to display the supported number range.

Step 3

bfd per-link

Example:

switch(config-if)# bfd per-link

Configures the BFD sessions for each link in the port channel.

Step 4

bfd interval mintx min_rx msec multiplier value

Example:

switch(config-if)# bfd interval 50
min_rx 50 multiplier 3

(Optional) Configures the BFD session parameters for all BFD sessions on the port channel. This command overrides these values by configuring the BFD session parameters. The mintx and msec range is from 50 to 999 milliseconds and the default is 50. The multiplier range is from 1 to 50. The multiplier default is 3.

Step 5

bfd authentication keyed-sha1 keyid id key ascii_key

Example:

switch(config-if)# bfd authentication
keyed-sha1 keyid 1 ascii_key cisco123

(Optional) Configures SHA-1 authentication for all BFD sessions on the interface. The ascii_key string is a secret key shared among BFD peers. The id value, a number between 0 and 255, is assigned to this particular ascii_key . BFD packets specify the key by id , allowing the use of multiple active keys.

To disable SHA-1 authentication on the interface, use the no form of the command.

Step 6

show running-config bfd

Example:

switch(config-if)# show running-config bfd

(Optional) Displays the BFD running configuration.

Step 7

copy running-config startup-config

Example:

switch(config-if)# copy running-config startup-config

(Optional) Saves the configuration change.

Configure the BFD Echo function (task)

You can configure the BFD echo function on one or both ends of a BFD-monitored link. The echo function slows down the required minimum receive interval, based on the configured slow timer. The RequiredMinEchoRx BFD session parameter remains nonzero if you disable the echo function to comply with RFC 5880 When you enable the echo function, the slow timer value becomes the required minimum receive interval.

Before you begin

Enable the BFD feature. See the Enable BFD feature.

Configure the BFD session parameters. See Configuring Global BFD Parameters or Configuring BFD on an Interface.

Disable Internet Control Message Protocol (ICMP) redirect messages on BFD-enabled interfaces using the no ip redirects command on the interface.

Procedure

Step 1

Enter the configuration mode using the configure terminal command.

Example:

switch# configure terminal
switch(config)#

Step 2

Set the slow timer to determine when BFD starts a new sesion using the bfd slow-timer echo-interval command.

Example:

switch(config)# bfd slow-timer 2000

When the BFD echo function is enabled, this value also slows down the asynchronous sessions.

This value overwrites the required minimum receive interval when the echo function is enabled. The range is from 1000 to 30,000 milliseconds. The default is 2000 milliseconds.

Step 3

Enters interface configuration mode using the interface int-if command.

Example:

switch(config)# interface ethernet 2/1
switch(config-if)#

Use the ? keyword to display the supported interfaces.

Step 4

Enable the echo function using the bfd echo command.

Example:

switch(config-if)# bfd echo

The default is enabled.

Step 5

(Optional) Display the BFD running configuration using the show running-config bfd command.

Example:

switch(config-if)# show running-config bfd

Step 6

(Optional) Saves the configuration using the copy running-config startup-config command.

Example:

switch(config-if)# copy running-config startup-config

Configuring Per-Member Link BFD Sessions

BFD per-member link support is added on Cisco Nexus 9000 Series switches. See the following sections for more information.

BFD Enhancement to Address Per-link Efficiency

The Bidirectional Forwarding (BFD) enhancement to address per-link efficiency, called as IETF Micro BFD, lets you configure the individual BFD sessions on every Link Aggregation Group (LAG) member interfaces (as defined in RFC 7130).

With this enhancement, the BFD sessions run on each member link of the port-channel. If BFD detects a link failure, the member link is removed from the forwarding table. This mechanism delivers faster failure detection as the BFD sessions are created on an individual port-channel interface.

The BFD sessions running on member links of the port-channel are called as Micro BFD sessions. You can configure RFC 7130 BFD over main port-channel interface, that performs bandwidth monitoring over LAG by having one Micro BFD session over each member. If any of the member port goes down, the port is removed from the forwarding table and this prevents traffic disruption on that member.

Micro BFD sessions are supported for both LACP and non-LACP based-port channels. For more information on how to configure Micro BFD sessions, see Configuring Micro BFD Sessions.

Limitations of the IETF Bidirectional Forwarding Detection

See the following limitations of the IETF Bidirectional Forwarding Detection:

  • BFD Limitations

    • IETF Micro-BFD sessions supports only single-hop BFD sessions. We recommend that you do not configure IPs from different subnets to establish the Micro-BFD sessions.

    • It cannot co-exist with BFD over logical port-channels or proprietary BFD per-member links. BFD IPv6 logical/proprietary per-link session is also not supported when BFD IETF IPv4 is configured on PC.

    • When you configure logical BFD session under any routing protocol, make sure that is not applied to any IETF port-channel. Having both logical and IETF configuration for same port-channel results in undefined behavior during ISSU/reloads.

    • IETF BFD IPv6 is not supported.

    • Echo functionality is not supported for Micro-BFD sessions.

    • Port-channel interfaces should be directly connected between two switches that are running the BFD sessions. No intermediate Layer 2 switches are expected.

  • EthPCM/LACP Limitations

    • If a LACP port-channel has members in hot-standby state, BFD failure in one of the active links may not cause the hot-standby link to come up directly. Once the active link with BFD failure goes down, the hot-standby member becomes active. However, it may not be able to prevent the port-channel from going down before the hot-standby link comes up, in cases where port-channel min-link condition is hit.

  • General Limitations:

    • It is supported only on Layer 3 port-channels.

    • It is not supported on the following:

      • vPC

      • Layer 3 sub-interfaces

      • Layer 2 port-channels/Layer 2 Fabric Path

      • FPC/HIF PC

      • Layer 3 sub-interfaces

      • SVI over port-channels

Guidelines for Migration/Configuration of IETF Per-Member Sessions:

See the following guidelines for migration/configuration of IETF per-member sessions:

  • The logical BFD sessions that are created using the routing protocols over port-channel sub-interfaces (where RFC 7130 cannot run) are still supported. The main port-channel interface however does not support both logical and RFC 7130 sessions that co-exist. It can support only either of them.

  • You can configure RFC 7130 BFD over the main port-channel interface that perform bandwidth monitoring over the LAG by having one Micro-BFD session over each member. If any of the member port goes down, BFD notifies it to the port-channel manager that removes the port from the LTL, thereby preventing blackholing of the traffic on that member.

  • If the minimum number of links required to have the port-channel operationally up is not met in the above case, the port-channel is brought down by the port-channel manager. This in turn brings down the port-channel sub-interfaces if they are configured and thereby the logical BFD session also comes down notifying the routing protocol.

  • When you are using RFC 7130 on the main port-channel and logical BFD on the sub-interfaces, the logical BFD session should be run with lesser aggressive timers than the RFC 7130 BFD session. You can have RFC 7130 configured on the port-channel interface or you can have it configured in conjunction with the logical BFD sessions on the port-channel sub-interfaces.

  • When a proprietary per-link is configured, enabling IETF Micro-BFD sessions is not allowed on a port channel and vice-versa. You have to remove the proprietary per-link configuration. Current implementation of proprietary per-link does not allow changing the configuration (no per-link), if there is any BFD session that is bootstrapped by the applications. You need to remove the BFD tracking on the respective applications and remove per-link configuration. The migration path from the proprietary per-link to IETF Micro-BFD is as follows:

    • Remove the BFD configuration on the applications.

    • Remove the per-link configuration.

    • Enable the IETF Micro-BFD command.

    • Enable BFD on the applications.

    The same migration path can be followed for proprietary BFD to IETF Micro-BFD on the main port-channel interface.

Configuring Port Channel Interface

Before you begin

Ensure that the BFD feature is enabled.

SUMMARY STEPS

  1. switch(config)# interface port-channel port-number
  2. switch(config-if)# no switchport

DETAILED STEPS

Step 1

switch(config)# interface port-channel port-number

Configures interface port-channel.

Step 2

switch(config-if)# no switchport

Configures interface as Layer 3 port-channel.

What to do next

  • Configuring BFD Start Timer

  • Enabling IETF Per-link BFD

(Optional) Configuring BFD Start Timer

Complete the following steps to configure the BFD start timer:

SUMMARY STEPS

  1. switch(config-if)# port-channel bfd start 60

DETAILED STEPS

switch(config-if)# port-channel bfd start 60

Configures the BFD start timer for a port-channel.

Note

 

The default value is infinite (that is no timer is running). The range of BFD Start Timer value for port-channel is from 60 to 3600 seconds. For start timer to work, configure start timer value before completing the port-channel BFD configurations (that is before port-channel bfd track-member-link and port-channel bfd destination are configured for Layer 3 port-channel interface with the active members).

What to do next

  • Enabling IETF Per-link BFD

  • Configuring BFD Destination IP Address

Enabling IETF Per-link BFD

SUMMARY STEPS

  1. switch(config-if)# port-channel bfd track-member-link

DETAILED STEPS

switch(config-if)# port-channel bfd track-member-link

Enables IETF BFD on port-channel interface.
What to do next

  • Configuring BFD Destination IP Address

  • Verifying Micro BFD Session Configurations

Configuring BFD Destination IP Address

Complete the following steps to configure the BFD destination IP address:

SUMMARY STEPS

  1. switch(config-if)# port-channel bfd destinationip-address

DETAILED STEPS

switch(config-if)# port-channel bfd destinationip-address

Configures an IPv4 address to be used for the BFD sessions on the member links.

What to do next

  • Verifying Micro BFD Sessions Configuration

Verifying Micro BFD Session Configurations

Use the following commands to verify the Micro BFD session configurations.

SUMMARY STEPS

  1. Displays the port-channel and port-channel member operational state.
  2. switch# show bfd neighbors
  3. switch# show bfd neighbors details
  4. switch# show tech-support bfd
  5. switch# show tech-support lacp all
  6. switch# show running-config interface port-channel port-channel-number

DETAILED STEPS

Step 1

Displays the port-channel and port-channel member operational state.

switch# show port-channel summary

Step 2

switch# show bfd neighbors

Displays Micro BFD sessions on port-channel members.

Step 3

switch# show bfd neighbors details

Displays BFD session for a port channel interface and the associated Micro BFD sessions on members.

Step 4

switch# show tech-support bfd

Displays the technical support information for BFD.

Step 5

switch# show tech-support lacp all

Displays the technical support information for Ethernet Port Manager, Ethernet Port-channel Manager, and LACP.

Step 6

switch# show running-config interface port-channel port-channel-number

Displays the running configuration information of the port-channel interface.

Examples: Configuring Micro BFD Sessions

See the following examples for configuring Micro BFD sessions.

Configuring Micro BFD Sessions

In this example, the following topology is used.

Figure 3. Configuring Micro BFD Session


The sample configuration of switch 1 is as follows:


feature bfd
configure terminal
    interface port-channel 10
       port-channel bfd track-member-link
       port-channel bfd destination 10.1.1.2
       port-channel bfd start 60
       ip address 10.1.1.1/24

The sample configuration of switch 2 is as follows:


feature bfd
configure terminal
     interface port-channel 10
           port-channel bfd track-member-link
           port-channel bfd destination 10.1.1.1
           port-channel bfd start 60
             ip address 10.1.1.2/24
Verifying Micro BFD Sessions Configuration

The following example displays the show output of the show running-config interface port-channel <port-channel>, show port-channel summary , show bfd neighbors vrf internet_routes , and show bfd neighbors interface port-channel <port-channel> vrf internet_routes details commands. 

switch# show running-config interface port-channel 1001

!Command: show running-config interface port-channel1001
!Time: Fri Oct 21 09:08:00 2016

version 7.0(3)I5(1)

interface port-channel1001
  no switchport
  vrf member internet_routes
  port-channel bfd track-member-link
  port-channel bfd destination 40.4.1.2
  ip address 40.4.1.1/24
  ipv6 address 2001:40:4:1::1/64

switch# show por
port-channel   port-profile   
switch# show port-channel summary 
Flags:  D - Down        P - Up in port-channel (members)
        I - Individual  H - Hot-standby (LACP only)
        s - Suspended   r - Module-removed
        b - BFD Session Wait
        S - Switched    R - Routed
        U - Up (port-channel)
        p - Up in delay-lacp mode (member)
        M - Not in use. Min-links not met
--------------------------------------------------------------------------------
Group Port-       Type     Protocol  Member Ports
      Channel
--------------------------------------------------------------------------------
1001  Po1001(RU)  Eth      LACP      Eth1/11/1(P)  Eth1/11/2(P)  Eth1/12/1(P)
                                     Eth1/12/2(P)  
switch# show bfd neighbors vrf internet_routes 

OurAddr         NeighAddr       LD/RD                 RH/RS           Holdown(mult)     State       Int                   Vrf                             
40.4.1.1        40.4.1.2        1090519041/0          Up              N/A(3)            Up          Po1001                internet_routes                 
40.4.1.1        40.4.1.2        1090519042/1090519051 Up              819(3)            Up          Eth1/12/1             internet_routes                 
40.4.1.1        40.4.1.2        1090519043/1090519052 Up              819(3)            Up          Eth1/12/2             internet_routes                 
40.4.1.1        40.4.1.2        1090519044/1090519053 Up              819(3)            Up          Eth1/11/1             internet_routes                 
40.4.1.1        40.4.1.2        1090519045/1090519054 Up              819(3)            Up          Eth1/11/2             internet_routes                 
switch# 

switch# show bfd neighbors interface port-channel 1001 vrf internet_routes details 

OurAddr         NeighAddr       LD/RD                 RH/RS           Holdown(mult)     State       Int                   Vrf                             
40.4.1.1        40.4.1.2        1090519041/0          Up              N/A(3)            Up          Po1001                internet_routes                 

Session state is Up
Local Diag: 0
Registered protocols:  eth_port_channel
Uptime: 1 days 11 hrs 4 mins 8 secs
Hosting LC: 0, Down reason: None, Reason not-hosted: None
Parent session, please check port channel config for member info
switch#

switch# show bfd neighbors interface ethernet 1/12/1 vrf internet_routes details 

OurAddr         NeighAddr       LD/RD                 RH/RS           Holdown(mult)     State       Int                   Vrf                             
40.4.1.1        40.4.1.2        1090519042/1090519051 Up              604(3)            Up          Eth1/12/1             internet_routes                 

Session state is Up and not using echo function
Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None
MinTxInt: 100000 us, MinRxInt: 100000 us, Multiplier: 3
Received MinRxInt: 300000 us, Received Multiplier: 3
Holdown (hits): 900 ms (0), Hello (hits): 300 ms (458317)
Rx Count: 427188, Rx Interval (ms) min/max/avg: 19/1801/295 last: 295 ms ago
Tx Count: 458317, Tx Interval (ms) min/max/avg: 275/275/275 last: 64 ms ago
Registered protocols:  eth_port_channel
Uptime: 1 days 11 hrs 4 mins 24 secs
Last packet: Version: 1                - Diagnostic: 0  
             State bit: Up             - Demand bit: 0  
             Poll bit: 0               - Final bit: 0  
             Multiplier: 3             - Length: 24  
             My Discr.: 1090519051     - Your Discr.: 1090519042  
             Min tx interval: 300000   - Min rx interval: 300000  
             Min Echo interval: 300000 - Authentication bit: 0  
Hosting LC: 1, Down reason: None, Reason not-hosted: None
Member session under parent interface Po1001


switch# show bfd neighbors interface ethernet 1/12/2 vrf internet_routes details 

OurAddr         NeighAddr       LD/RD                 RH/RS           Holdown(mult)     State       Int                   Vrf                             
40.4.1.1        40.4.1.2        1090519043/1090519052 Up              799(3)            Up          Eth1/12/2             internet_routes                 

Session state is Up and not using echo function
Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None
MinTxInt: 100000 us, MinRxInt: 100000 us, Multiplier: 3
Received MinRxInt: 300000 us, Received Multiplier: 3
Holdown (hits): 900 ms (0), Hello (hits): 300 ms (458336)
Rx Count: 427207, Rx Interval (ms) min/max/avg: 19/1668/295 last: 100 ms ago
Tx Count: 458336, Tx Interval (ms) min/max/avg: 275/275/275 last: 251 ms ago
Registered protocols:  eth_port_channel
Uptime: 1 days 11 hrs 4 mins 30 secs
Last packet: Version: 1                - Diagnostic: 0  
             State bit: Up             - Demand bit: 0  
             Poll bit: 0               - Final bit: 0  
             Multiplier: 3             - Length: 24  
             My Discr.: 1090519052     - Your Discr.: 1090519043  
             Min tx interval: 300000   - Min rx interval: 300000  
             Min Echo interval: 300000 - Authentication bit: 0  
Hosting LC: 1, Down reason: None, Reason not-hosted: None
Member session under parent interface Po1001
switch#

Configuring BFD Support for Routing Protocols

Configuring BFD on BGP

You can configure BFD for the Border Gateway Protocol (BGP).

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.

Enable the BGP feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. router bgp as-number
  3. neighbor (ip-address | ipv6-address) remote-as as-number
  4. bfd [multihop | singlehop]
  5. update-source interface
  6. show running-config bgp
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

router bgp as-number

Example:

switch(config)# router bgp 64496
switch(config-router)#

Enables BGP and assigns the AS number to the local BGP speaker. The AS number can be a 16-bit integer or a 32-bit integer in the form of a higher 16-bit decimal number and a lower 16-bit decimal number in xx.xx format.

Step 3

neighbor (ip-address | ipv6-address) remote-as as-number

Example:

switch(config-router)# neighbor
209.165.201.1 remote-as 64497
switch(config-router-neighbor)#

Configures the IPv4 or IPv6 address and AS number for a remote BGP peer. The ip-address format is x.x.x.x. The ipv6-address format is A:B::C:D.

Step 4

bfd [multihop | singlehop]

Example:

switch(config-router-neighbor)# bfd multiihop

Configures the BFD multi hop or single hop session on the device. The default is with no keyword. When you do not specify any keyword and if the peer is directly connected then a single hop session is selected, if the peer is not connected then a multi hop session type is selected. When you specify a "multihop" or "singlehop" option, the session type is forced in a device according to the CLI option.

Step 5

update-source interface

Example:

switch(config-router-neighbor)# update-source ethernet 2/1

Allows BGP sessions to use the primary IP address from a particular interface as the local address when forming a BGP session with a neighbor and enables BGP to register as a client with BFD.

Step 6

show running-config bgp

Example:

switch(config-router-neighbor)# show
running-config bgp

(Optional) Displays the BGP running configuration.

Step 7

copy running-config startup-config

Example:

switch(config-router-neighbor)# copy
running-config startup-config

(Optional) Saves the configuration change.

Configuring BFD on EIGRP

You can configure BFD for the Enhanced Interior Gateway Routing Protocol (EIGRP).

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.

Enable the EIGRP feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. router eigrp instance-tag
  3. bfd [ipv4 | ipv6]
  4. interface int-if
  5. ip eigrp instance-tag bfd
  6. show ip eigrp [vrf vrf-name] [ interfaces if]
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

router eigrp instance-tag

Example:

switch(config)# router eigrp Test1
switch(config-router)#

Creates a new EIGRP process with the configured instance tag. The instance tag can be any case-sensitive, alphanumeric string up to 20 characters.

If you configure an instance-tag that does not qualify as an AS number, you must use the autonomous-system to configure the AS number explicitly or this EIGRP instance will remain in the shutdown state.

Step 3

bfd [ipv4 | ipv6]

Example:

switch(config-router-neighbor)# bfd ipv4

(Optional) Enables BFD for all EIGRP interfaces.

Step 4

interface int-if

Example:

switch(config-router-neighbor)# interface
ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 5

ip eigrp instance-tag bfd

Example:

switch(config-if)# ip eigrp Test1 bfd

(Optional) Enables or disables BFD on an EIGRP interface. The instance tag can be any case-sensitive, alphanumeric string up to 20 characters.

The default is disabled.

Step 6

show ip eigrp [vrf vrf-name] [ interfaces if]

Example:

switch(config-if)# show ip eigrp

(Optional) Displays information about EIGRP. The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters.

Step 7

copy running-config startup-config

Example:

switch(config-if)# copy
running-config startup-config

(Optional) Saves the configuration change.

Configuring BFD on OSPF

You can configure BFD for the Open Shortest Path First.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.

Enable the OSPF feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. router ospf instance-tag
  3. bfd [ipv4 | ipv6]
  4. interface int-if
  5. ip ospf bfd
  6. show ip ospf [vrf vrf-name] [ interfaces if]
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

router ospf instance-tag

Example:

switch(config)# router ospf 200
switch(config-router)#

Creates a new OSPF instance with the configured instance tag. The instance tag can be any case-sensitive, alphanumeric string up to 20 characters.

Step 3

bfd [ipv4 | ipv6]

Example:

switch(config-router)# bfd

(Optional) Enables BFD for all OSPF interfaces.

Step 4

interface int-if

Example:

switch(config-router)# interface
ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 5

ip ospf bfd

Example:

switch(config-if)# ip ospf bfd

(Optional) Enables or disables BFD on an OSPF interface. The default is disabled.

Step 6

show ip ospf [vrf vrf-name] [ interfaces if]

Example:

switch(config-if)# show ip ospf

(Optional) Displays information about OSPF. The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters.

Step 7

copy running-config startup-config

Example:

switch(config-if)# copy
running-config startup-config

(Optional) Saves the configuration change.

Example Configurations for BFD on OSPF

Example configuration where BFD is enabled under a non-default VRF (OSPFv3 neighbors in vrf3). 

configure terminal
  router ospfv3 10
    vrf vrf3 
    bfd

Configuring BFD on IS-IS

You can configure BFD for the Intermediate System-to-Intermediate System (IS-IS) protocol.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.

Enable the IS-IS feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. router isis instance-tag
  3. bfd [ipv4 | ipv6]
  4. interface int-if
  5. isis bfd
  6. show isis [vrf vrf-name] [ interface if]
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

router isis instance-tag

Example:


switch(config)# router isis 100
  switch(config-router)# net 49.0001.1720.1600.1001.00
  switch(config-router)# address-family ipv6 unicast

Creates a new IS-IS instance with the configured instance tag .

Step 3

bfd [ipv4 | ipv6]

Example:

switch(config-router)# bfd

(Optional) Enables BFD for all OSPF interfaces.

Step 4

interface int-if

Example:

switch(config-router)# interface
ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 5

isis bfd

Example:

switch(config-if)# isis bfd

(Optional) Enables or disables BFD on an IS-IS interface. The default is disabled.

Step 6

show isis [vrf vrf-name] [ interface if]

Example:

switch(config-if)# show isis

(Optional) Displays information about IS-IS. The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters.

Step 7

copy running-config startup-config

Example:

switch(config-if)# copy
running-config startup-config

(Optional) Saves the configuration change.

Example Configurations for BFD on IS-IS

Example configuration for IS-IS where BFD is enabled under IPv4 and an IPv6 address family. 

configure terminal
  router isis isis-1 
    bfd      
    address-family ipv6 unicast 
    bfd

Configuring BFD on HSRP

You can configure BFD for the Hot Standby Router Protocol (HSRP). The active and standby HSRP routers track each other through BFD. If BFD on the standby HSRP router detects that the active HSRP router is down, the standby HSRP router treats this event as an active time rexpiry and takes over as the active HSRP router.

The show hsrp detail command shows this event as BFD@Act-down or BFD@Sby-down.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.

Enable the HSRP feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. hsrp bfd all-interfaces
  3. interface int-if
  4. hsrp bfd
  5. show running-config hsrp
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

hsrp bfd all-interfaces

Example:

switch# hsrp bfd all-interfaces

(Optional) Enables or disables BFD on all HSRP interfaces. The default is disabled.

Step 3

interface int-if

Example:

switch(config-router)# interface
ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 4

hsrp bfd

Example:

switch(config-if)# hsrp bfd

(Optional) Enables or disables BFD on an HSRP interface. The default is disabled.

Step 5

show running-config hsrp

Example:

switch(config-if)# show running-config hsrp

(Optional) Displays the HSRP running configuration.

Step 6

copy running-config startup-config

Example:

switch(config-if)# copy
running-config startup-config

(Optional) Saves the configuration change.

Configuring BFD on VRRP

You can configure BFD for the Virtual Router Redundancy Protocol (VRRP). The active and standby VRRP routers track each other through BFD. If BFD on the standby VRRP router detects that the active VRRP router is down, the standby VRRP router treats this event as an active time rexpiry and takes over as the active VRRP router.

The show vrrp detail command shows this event as BFD@Act-down or BFD@Sby-down.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.

Enable the VRRP feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. interface int-if
  3. vrrp group-no
  4. vrrp bfd address
  5. show running-config vrrp
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface int-if

Example:

switch(config)# interface
ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 3

vrrp group-no

Example:

switch(config-if)# vrrp 2

Specifies the VRRP group number.

Step 4

vrrp bfd address

Example:

switch(config-if)# vrrp bfd

Enables or disables BFD on a VRRP interface. The default is disabled.

Step 5

show running-config vrrp

Example:

switch(config-if)# show running-config vrrp

(Optional) Displays the VRRP running configuration.

Step 6

copy running-config startup-config

Example:

switch(config-if)# copy
running-config startup-config

(Optional) Saves the configuration change.

Configuring BFD on PIM

You can configure BFD for the Protocol Independent Multicast (PIM) protocol.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

Enable the PIM feature. See the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide for more information.

SUMMARY STEPS

  1. configure terminal
  2. ip pim bfd
  3. interface int-if
  4. ip pim bfd-instance [disable]
  5. show running-config pim
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

ip pim bfd

Example:

switch(config)# ip pim bfd

Enables BFD for PIM.

Step 3

interface int-if

Example:

switch(config)# interface
ethernet 2/1
switch(config-if)#

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 4

ip pim bfd-instance [disable]

Example:

switch(config-if)# ip pim bfd-instance

(Optional) Enables or disables BFD on a PIM interface. The default is disabled.

Step 5

show running-config pim

Example:

switch(config)# show running-config pim

(Optional) Displays the PIM running configuration.

Step 6

copy running-config startup-config

Example:

switch(config)# copy
running-config startup-config

(Optional) Saves the configuration change.

Configuring BFD on Static Routes

You can configure BFD for static routes on an interface. You can optionally configure BFD on a static route within a virtual routing and forwarding (VRF) instance.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

SUMMARY STEPS

  1. configure terminal
  2. vrf context vrf-name
  3. ip route route interface {nh-address | nh-prefix}
  4. ip route static bfd interface {nh-address | nh-prefix}
  5. show ip route static [vrf vrf-name]
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

vrf context vrf-name

Example:

switch(config)# vrf context Red
switch(config-vrf)#

(Optional) Enters VRF configuration mode.

Step 3

ip route route interface {nh-address | nh-prefix}

Example:

switch(config-vrf)# ip route 192.0.2.1 ethernet 2/1 192.0.2.4

Creates a static route Use the ? keyword to display the supported interfaces.

Step 4

ip route static bfd interface {nh-address | nh-prefix}

Example:

switch(config-vrf)# ip route static bfd ethernet 2/1 192.0.2.4

Enables BFD for all static routes on an interface. Use the? keyword to display the supported interfaces.

Step 5

show ip route static [vrf vrf-name]

Example:

switch(config-vrf)# show ip route static vrf Red

(Optional) Displays the static routes.

Step 6

copy running-config startup-config

Example:

switch(config-vrf)# copy
running-config startup-config

(Optional) Saves the configuration change.

Disabling BFD on an Interface

You can selectively disable BFD on an interface for a routing protocol that has BFD enabled at the global or VRF level.

To disable BFD on an interface, use one of the following commands in interface configuration mode:

Command

Purpose

ip eigrp instance-tag bfd disable

Example: 
switch(config-if)# ip eigrp Test1 bfd
disable

Disables BFD on an EIGRP interface. The instance tag can be any case-sensitive, alphanumeric string up to 20 characters.

ip ospf bfd disable

Example: 
switch(config-if)# ip ospf bfd disable

Disables BFD on an OSPFv2 interface.

isis bfd disable

Example: 
switch(config-if)# isis bfd disable

Disables BFD on an IS-IS interface.

Disabling BFD on an Interface

Example configuration where BFD is disabled per interface. 

configure terminal
  interface port-channel 10
    no ip redirects
    ip address 22.1.10.1/30
    ipv6 address 22:1:10::1/120
    no ipv6 redirects
    ip router ospf 10 area 0.0.0.0
    ip ospf bfd disable        /*** disables IPv4 BFD session for OSPF
    ospfv3 bfd disable 		      /*** disables IPv6 BFD session for OSPFv3

Configuring BFD Interoperability

Configuring BFD Interoperability in Cisco NX-OS Devices in a Point-to-Point Link

SUMMARY STEPS

  1. configure terminal
  2. interface port-channel int-if
  3. ip ospf bfd
  4. no ip redirects
  5. bfd interval mintx min_rx msec multiplier value
  6. exit

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface port-channel int-if

Example:

switch(config-if)# interface ethernet 2/1

Enters interface configuration mode. Use the ? keyword to display the supported interfaces.

Step 3

ip ospf bfd

Example:

switch(config-if)# ip ospf bfd

Enables BFD on an OSPFv2 interface. The default is disabled.

OSPF is used as an example. You can enable BFD of any of the supported protocols.

Step 4

no ip redirects

Example:

switch(config-if)# no ip redirects

Prevents the device from sending redirects.

Step 5

bfd interval mintx min_rx msec multiplier value

Example:

switch(config-if)# bfd interval 50
min_rx 50 multiplier 3

Configures the BFD session parameters for all BFD sessions on the port channel. This command overrides these values by configuring the BFD session parameters. The mintx and msec range is from 50 to 999 milliseconds and the default is 50. The multiplier range is from 1 to 50. The multiplier default is 3.

Step 6

exit

Example:

switch(config-if)# exit

Exits interface configuration mode and returns to EXEC mode.

Configuring BFD Interoperability in Cisco NX-OS Devices in a Switch Virtual Interface

SUMMARY STEPS

  1. configure terminal
  2. interface port-channel vlan vlan-id
  3. bfd interval mintx min_rx msec multiplier value
  4. no ip redirects
  5. ip address ip-address/length
  6. ip ospf bfd
  7. exit

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface port-channel vlan vlan-id

Example:

switch(config)# interface vlan 998
switch(config-if)#

Creates a dynamic Switch Virtual Interface (SVI).

Step 3

bfd interval mintx min_rx msec multiplier value

Example:

switch(config-if)# bfd interval 50
min_rx 50 multiplier 3

Configures the BFD session parameters for all BFD sessions on the device. The mintx and msec range is from 50 to 999 milliseconds and the default is 50. The multiplier range is from 1 to 50. The multiplier default is 3.

Step 4

no ip redirects

Example:

switch(config-if)# no ip redirects

Prevents the device from sending redirects.

Step 5

ip address ip-address/length

Example:

switch(config-if)# ip address 10.1.0.253/24

Configures an IP address for this interface.

Step 6

ip ospf bfd

Example:

switch(config-if)# ip ospf bfd

Enables BFD on an OSPFv2 interface. The default is disabled.

Step 7

exit

Example:

switch(config-if)# exit

Exits interface configuration mode and returns to EXEC mode.

Configuring BFD Interoperability in Cisco NX-OS Devices in Logical Mode

SUMMARY STEPS

  1. configure terminal
  2. interface port-channel type number.subinterface-id
  3. bfd interval mintx min_rx msec multiplier value
  4. no ip redirects
  5. ip ospf bfd
  6. exit

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface port-channel type number.subinterface-id

Example:

switch(config-if)# interface port-channel 50.2

Enters port channel configuration mode. Use the ? keyword to display the supported number range.

Step 3

bfd interval mintx min_rx msec multiplier value

Example:

switch(config-if)# bfd interval 50
min_rx 50 multiplier 3

Configures the BFD session parameters for all BFD sessions on the port channel. The mintx and msec range is from 50 to 999 milliseconds and the default is 50. The multiplier range is from 1 to 50. The multiplier default is 3.

Step 4

no ip redirects

Example:

switch(config-if)# no ip redirects

Prevents the device from sending redirects.

Step 5

ip ospf bfd

Example:

switch(config-if)# ip ospf bfd

Enables BFD on an OSPFv2 interface. The default is disabled.

OSPF is used as an example. You can enable BFD of any of the supported protocols.

Step 6

exit

Example:

switch(config-if)# exit

Exits interface configuration mode and returns to EXEC mode.

Verifying BFD Interoperability in a Cisco Nexus 9000 Series Device

The following example shows how to verify BFD interoperability in a Cisco Nexus 9000 Series device. 


switch# show bfd neighbors details
OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int
Vrf
10.1.1.1 10.1.1.2 1140850707/2147418093 Up 6393(4) Up Vlan2121
default
Session state is Up and using echo function with 50 ms interval
Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None
MinTxInt: 50000 us, MinRxInt: 2000000 us, Multiplier: 3
Received MinRxInt: 2000000 us, Received Multiplier: 4
Holdown (hits): 8000 ms (0), Hello (hits): 2000 ms (108)
Rx Count: 92, Rx Interval (ms) min/max/avg: 347/1996/1776 last: 1606 ms ago
Tx Count: 108, Tx Interval (ms) min/max/avg: 1515/1515/1515 last: 1233 ms ago
Registered protocols: ospf
Uptime: 0 days 0 hrs 2 mins 44 secs
Last packet: Version: 1 - Diagnostic: 0
State bit: Up - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 4 - Length: 24
My Discr.: 2147418093 - Your Discr.: 1140850707
Min tx interval: 2000000 - Min rx interval: 2000000
Min Echo interval: 1000 - Authentication bit: 0
Hosting LC: 10, Down reason: None, Reason not-hosted: None



switch# show bfd neighbors details
OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int
Vrf
10.0.2.1 10.0.2.2 1140850695/131083 Up 270(3) Up Po14.121
default
Session state is Up and not using echo function
Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None
MinTxInt: 50000 us, MinRxInt: 50000 us, Multiplier: 3
Received MinRxInt: 100000 us, Received Multiplier: 3
Holdown (hits): 300 ms (0), Hello (hits): 100 ms (3136283)
Rx Count: 2669290, Rx Interval (ms) min/max/avg: 12/1999/93 last: 29 ms ago
Tx Count: 3136283, Tx Interval (ms) min/max/avg: 77/77/77 last: 76 ms ago
Registered protocols: ospf
Uptime: 2 days 21 hrs 41 mins 45 secs
Last packet: Version: 1 - Diagnostic: 0
State bit: Up - Demand bit: 0
Poll bit: 0 - Final bit: 0
Multiplier: 3 - Length: 24
My Discr.: 131083 - Your Discr.: 1140850695
Min tx interval: 100000 - Min rx interval: 100000
Min Echo interval: 0 - Authentication bit: 0
Hosting LC: 8, Down reason: None, Reason not-hosted: None

Verifying the BFD Configuration

To display BFD configuration information, perform one of the following:

Command

Purpose

show running-config bfd

Displays the running BFD configuration.

show startup-config bfd

Displays the BFD configuration that will be applied on the next system startup.

Monitoring BFD

Use the following commands to display BFD:

Command

Purpose

show bfd neighbors [application name] [details]

Displays information about BFD for a supported application, such as BGP or OSPFv2.

show bfd neighbors [interface int-if] [details]

Displays information about BFD neighbors on an interface.

show bfd neighbors [dest-ip ip-address] [src-ip ip-address][details]

Displays information about the specified BFD neighbors on an interface.

show bfd neighbors [vrf vrf-name] [details]

Displays information about BFD for a VRF.

show bfd [ipv4 | ipv6] [neighbors]

Displays information about IPv4 neighbors or IPv6 neighbors.

BFD Multi-sessions (concept)

A BFD multi-session is a network management capability that:

  • allows multiple BFD sessions to be set up over a single network link,

  • enhances network reliability by enabling quick fault detection,

  • enables detailed monitoring of multiple paths over a single link, and

  • optimizes resource use and scalability.

Starting with Cisco NX-OS Release 10.5(3)F, Cisco Nexus switches support BFD multi-sessions.

BFD Multihop

BFD multihop for IPv4 and BFD multihop for IPv6 are supported in compliance with RFC5883. BFD multihop sessions are set up between a unique source and destination address pair. A multihop BFD session is associated with the link between a source and destination rather than with an interface, as with single-hop BFD sessions.

BFD Multihop Number of Hops

BFD multihop sets the TTL field to the maximum limit, and it does not check the value on reception. The BFD code has no impact on the number of hops a BFD multihop packet can traverse. However, in most of the systems, it limits the number of hops to 255.

Guidelines and Limitations for BFD Multihop

BFD multihop has the following configuration guidelines and limitations:

  • Beginning with Cisco NX-OS Release 10.4 (1)F, BFD multihop over VXLAN with L3VNI interfaces is supported.

  • Beginning with Cisco NX-OS Release 9.3(6), BFD multihop is only supported in BGP IPv4 on Cisco Nexus 9200, 9300-EX/FX/GX platform switches and Cisco Nexus 9500 platform switches with N9K-X9700-EX line cards.

  • In a dynamic BGP configuration, both the single and multihop BGP peers accepts BFD multihop configuration.

  • BFD multihop is only supported with BGP.

  • BFD multihop is supported for BGP IPv6 multihop neighbors on the following devices:

    • Cisco Nexus 9200YC-X, 9300-EX, 9300-FX and 9300-GX switches

    • Cisco Nexus 9500 platform switches with N9K-X9736C-EX, N9K-X97160YC-EX, N9K-X9732C-EX, , or N9K-X9736C-FX line cards


      Note

      You must enable the system routing template-mpls-heavy command in order to use BFD multihop for BGP IPv6 with Cisco Nexus 9500 platform switches with -EX and -FX line cards.

  • Multihop BFD is identified with UDP Destination port 4784.

  • The default interval timer for multihop BFD is 250 ms with multiplier 3.

  • The maximum number of supported multihop BFD sessions is 100.​

  • Existing BFD authentication support is extended for multihop sessions.

  • Echo mode is not supported for multihop BFD.

  • Multihop with segment routing underlay is not supported.

  • On unsupported platforms, BFD commands are accepted when configuring BGPv6 multihop neighbors. However, the sessions will not be created or installed.

  • When Multihop BFD session is installed in port-channel, the following points must be taken care:

    • If all the sessions are hosted on a single line card of Cisco Nexus 9500 family switches, during reloading of hosted line cards all the sessions will be hosted on another line card. BFD and BGP sessions may flap in this case.

    • Multihop BFD session for BGP over cross modules port-channel doesn't provide full redundancy.

Configuring BFD Multihop Session Global Interval Parameters

You can configure the BFD session global parameters for all BFD sessions on the device. Different BFD session parameters for each session can be achieved using the per session configuration commands .

Before you begin

Enable the BFD feature.

SUMMARY STEPS

  1. configure terminal
  2. [no] bfd multihop interval milliseconds min_rx milliseconds multiplier interval-multiplier
  3. end

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

[no] bfd multihop interval milliseconds min_rx milliseconds multiplier interval-multiplier

Example:

switch(config)# bfd multihop interval 250 min_rx
 250 multiplier 3

Configures the BFD multihop session global parameters for all BFD sessions on the device. This command overrides the default values. The Required Minimum Receive Interval and Desired Minimum Transmit Interval are 250. The multiplier default is 3.

Step 3

end

Example:

switch(config)# end

Saves the configuration change and ends the configuration session.

Configuring Per Multihop Session BFD Parameters

You can configure per multihop session BFD parameters.

Before you begin

Enable the BFD feature. See the Enabling the BFD Feature section.

SUMMARY STEPS

  1. configure terminal
  2. router bgp as-number
  3. neighbor (ip-address | ipv6-address) remote-as as-number
  4. update-source interface
  5. bfd
  6. bfd multihop interval mintx min_rx msec multiplier value
  7. bfd multihop authentication keyed-sha1 keyid id key ascii_key
  8. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters configuration mode.

Step 2

router bgp as-number

Example:

switch(config)# router bgp 64496
switch(config-router)#

Enables BGP and assigns the AS number to the local BGP speaker. The AS number can be a 16-bit integer or a 32-bit integer in the form of a higher 16-bit decimal number and a lower 16-bit decimal number in xx.xx format.

Step 3

neighbor (ip-address | ipv6-address) remote-as as-number

Example:

switch(config-router)# neighbor
209.165.201.1 remote-as 64497
switch(config-router-neighbor)#

Configures the IPv4 or IPv6 address and AS number for a remote BGP peer. The ip-address format is x.x.x.x. The ipv6-address format is A:B::C:D.

Step 4

update-source interface

Example:

switch(config-router-neighbor)# update-source Ethernet1/4
switch(config-router-neighbor)#

Retrieves the source IP address of the BFD session from the interface.

Step 5

bfd

Example:

switch(config-router-neighbor)# bfd multihop

Enables BFD for this BGP peer.

Step 6

bfd multihop interval mintx min_rx msec multiplier value

Example:

switch(config-router-neighbor)# bfd multihop interval 250
min_rx 250 multiplier 3

Configures Multihop BFD interval values for this neighbor. The mintx and msec range is from 250 to 999 milliseconds and the default is 250. The multiplier range is from 1 to 50. The multiplier default is 3.

Step 7

bfd multihop authentication keyed-sha1 keyid id key ascii_key

Example:

switch(config-router-neighbor)# bfd multihop authentication
keyed-sha1 keyid 1 ascii_key cisco123

(Optional) Configures SHA-1 authentication for BFDs on Multihop BFD session over this neighbor. The ascii_key string is a secret key shared among BFD peers. The id value, a number between 0 and 255, is assigned to this particular ascii_key . BFD packets specify the key by id , allowing the use of multiple active keys.

To disable SHA-1 authentication on the interface, use the no form of the command.

Step 8

copy running-config startup-config

Example:

switch(config-router-neighbor)# copy
running-config startup-config

(Optional) Saves the configuration change.

BFD vPC sub-second convergence in failure scenarios

vPC (Virtual Port Channel) convergence refers to how quickly the network recovers from failures or topology changes involving vPC setups. During a power failure, switches handling vPC multicast traffic may face convergence delays of 6 to 7 seconds.

The BFD vPC watch sub-second convergence feature allows paired vPC switches to converge Multicast traffic within 250ms in scenarios when a single link fails in the network or a single switch goes offline due to power failure.

Beginning with Cisco NX-OS Release 10.5(3)F, this feaure is supported only on PIM protocols to handle the BFD vPC watch notifications.


Note

This features does not apply on other IGP protocols.

Benefits of vPC Sub-second Convergence

  • Rapid Convergence: Provides multicast traffic convergence within 250 ms during network failures for these traffic flows.

    • vPC to vPC

    • vPC to Layer 3

    • Layer 3 to vPC and,

    • Layer 3 to Layer 3

  • Efficient Multicast Handling: Addresses the delays in multicast traffic failover, improving overall network performance.

  • Enhanced Network Resilience: Provides a robust solution for maintaining network operations during unexpected failures. Handles scenarios like single link failure or switch power-off, ensuring quick failover with minimal traffic loss.

  • Platform Support: Specifically optimized for Cisco Nexus 9000 TOR platforms (FX2, FX3, and Cloudscale TORs).

BFD vPC Watch Configuration Workflow

  1. Enable BFD feature configuration on the switch and establish a dedicated port-channel between vPC peers for fast detection.

  2. Configure the port-channel bfd track-member-link command on the port-channel to create the micro-BFD session on a dedicated port-channel to detect any failures in the VPC peer.

    The micro-BFD session operates at aggressive intervals of a minimum of 10 ms, with a configured multiplier.

  3. Enable the bfd vpc-watch command on port-channel interfaces to identify the vPC monitoring.

    The vPC switch trigger event broadcasts the State Change Notifications (SCN) of the micro-BFD session to all subscribers on port-channel interfaces.

  4. The Protocol Independent Multicast (PIM) receives the BFD notifications for Micro-BFD sessions and maintains the sessions.

Restrictions

  • BFD vPC Watch feature is supported only on these Cisco Nexus switches.

    • N9K-X9736C-FX, N9K-X9736Q-FX, N9K-X9788TC-FX, N9K-C93180YC-FXN9K-C93108TC-FX, N9K-C9348GC-F, N9K-C9348GC-FXP, N9K-C9358GY-FXP, N9K-X9732C-FX, N9K-C92348GC-X

    • N9K-C9336C-FX2-E, N9K-C93216TC-FX2, N9K-C93360YC-FX2, N9K-C93240YC-FX2-Z, N9K-C93240YC-FX2,N9K-C9336C-FX2

    • N9K-C9316D-GX, N9K-C93600CD-GX, N9K-C9364C-GX, N9K-X9716D-GX,

    • N9K-X9736C-FX3, N9K-C93180YC-FX3S, N9K-C93180YC-FX3, N9K-C93108TC-FX3P,N9K-C9348GC-FX3, N9K-C9348GC-FX3PH, N9K-C93108TC-FX3, N9K-C92348GC-FX3

    • N9K-C9364D-GX2A, N9K-C9332D-GX2B, N9K-C9348D-GX2A, N9K-C9408

    • N9K-C9332D-H2R, N9K-C9364C-H1, N9K-C93400LD-H1

  • The bfd vpc-watch command is applicable on port-channel interfaces with the port-channel bfd track-member-link configuration.


    Note

    Before removing the port-channel bfd track-member-link configuration, make sure to unconfigure the bfd vpc-watch .

  • If bfd vpc-watch is configured on the VPC watchdog port-channel interface, performing any administrative operations that bring down the micro-BFD session on this interface or its member links could result in traffic duplication. To prevent this issue, remove the bfd vpc-watch configuration before carrying out any administrative tasks on the VPC watchdog interface.

  • A warning message appears on feature bfd configuration.

    Supported BFD session scale limit is 10 when TX interval or RX interval or Echo-rx-interval is configured less than 50ms.

  • BFD interval multiplier 1 is not supported when any of the Tx, Rx ro eho-rx intervals are configured less than 50 ms.

  • Cisco NX-OS Release 10.5(3)F release does not support Micro-BFD IPv6 sessions.

  • Starting with Cisco NX-OS Release 10.5(3)F, the TX, RX intervals for BFD IPv4 and IPv6 sessions ranges from 10-999 ms.

    In release before Cisco NX-OS Release 10.5(3)F, the TX and RX intervals for BFD IPv4 and IPv6 sessions ranges from 50-999 ms.

    You can set the interval using the bfd [ ipv4 | ipv6 ] interval msec [min_rx msec multiplier interval-multiplier] command.

  • Starting with Cisco NX-OS Release 10.5(3)F, the BFD Echo-rx intervals for BFD IPv4 and IPv6 Echo sessions ranges from 10-999 ms.

    In release before Cisco NX-OS Release 10.5(3)F, the BFD Echo intervals for IPv4 and IPv6 sessions ranges from 50-999 ms.

    You can set the interval using the bfd [ ipv4 | ipv6 ] echo-rx-interval msec command.

Configure BFD vPC Sub-second Convergence

To enable vPC convergence on the switches, follow these steps.

Before you begin

Configure BFD feature on the switch.

Procedure

Step 1

Enter configuration mode using the configure terminal command.

Example:

switch# configure

Step 2

Enable BFD configurations on the vPC switches using the feature bfd command.

Example:

switch# feature bfd
switch(config)#

Step 3

Enter the port-channel configuration mode using the interface port-channel number command.

Use the ? keyword to display the supported number range.

Example:

switch(config)# interface port-channel 2
switch(config-if)#

Step 4

Enable the IETF BFD on port-channel interface using the port-channel bfd track-member-link command.

Note

 

The bfd vpc-watch command is configurable on the port-channel interface only if port-channel bfd track-member-link command is already configured.

Example:

switch(config-if)# port-channel bfd track-member-link

Step 5

Configure the VPC peer monitoring interface using the bfd vpc-watch command to enable BFD SCN notifications.

Example:

switch(config-if)# bfd vpc-watch
switch(config-if)#

Step 6

Configure the BFD session parameters for all BFD sessions on the port channel using the bfd interval [msec min_rx msec multiplier interval-multiplier] command.

This command overrides these values by configuring the BFD session parameters.

The required minimum receive interval min_rx msec and desired minimum transmit interval bfd interval msec range is from 10-999 ms. The default interval value is 50 ms.

The multiplier msec multiplier range is 1–50. The default multiplier value is 3.

Note

 

Use a BFD interval multiplier over 1 if the Tx/Rx timer is 10 ms.

Example:

switch(config-if)# bfd interval 10 min_rx 50 multiplier 3

Step 7

(Optional) Display the BFD running configuration using the show running-config bfd and show bfd neighbors interface port-channel details command.

Example:

switch(config)# show running-config bfd
interface port-channel45 
  port-channel bfd track-member-link 
  port-channel bfd destination 10.10.1.1 
  bfd vpc-watch ---> VPC watchdog session configuration. 

switch(config)# show bfd neighbors interface port-channel 45 details | no-more
 
Session state is AdminDown
Session type: Singlehop, Vpc-Watch: Enable
Local Diag: 7
Registered protocols:  eth_port_channe
AdminDown for 0 days 2 hrs 47 mins 16 secs
Hosting LC: 0, Down reason: None, Reason not-hosted: None
Parent session, please check port channel config for member info

Configuration Examples for BFD

This example shows how to configure BFD for OSPFv2 on Ethernet 2/1, using the default BFD session parameters: 


feature bfd
feature ospf
router ospf Test1
interface ethernet 2/1
ip ospf bfd
no shutdown

This example shows how to configure BFD for all EIGRP interfaces, using the default BFD session parameters: 


feature bfd
feature eigrp
bfd interval 100 min_rx 100 multiplier 4
router eigrp Test2
bfd

This example shows how to configure BFDv6: 


feature bfd
feature ospfv3
router ospfv3 Test1
interface Ethernet2/7
  ipv6 router ospfv3 Test1 area 0.0.0.0
  ospfv3 bfd
  no shutdown

Show Example for BFD

This example shows results of the show bfd ipv6 neighbors details command. 


#show bfd ipv6 neighbors details

OurAddr                          NeighAddr                        
 LD/RD                 RH/RS           Holdown(mult)     State       Int                   Vrf                             
cc:10::2                         cc:10::1                         
 1090519335/1090519260 Up              5692(3)           Up          Po1                   default                         


Session state is Up and using echo function with 250 ms interval
Local Diag: 0, Demand mode: 0, Poll bit: 0, Authentication: None
MinTxInt: 250000 us, MinRxInt: 2000000 us, Multiplier: 3
Received MinRxInt: 2000000 us, Received Multiplier: 3
Holdown (hits): 6000 ms (4), Hello (hits): 2000 ms (205229)
Rx Count: 227965, Rx Interval (ms) min/max/avg: 124/1520/1510 last: 307 ms ago
Tx Count: 205229, Tx Interval (ms) min/max/avg: 1677/1677/1677 last: 587 ms ago
Registered protocols:  bgp
Uptime: 3 days 23 hrs 31 mins 13 secs
Last packet: Version: 1                - Diagnostic: 0  
             State bit: Up             - Demand bit: 0  
             Poll bit: 0               - Final bit: 0  
             Multiplier: 3             - Length: 24  
             My Discr.: 1090519260     - Your Discr.: 1090519335  
             Min tx interval: 250000   - Min rx interval: 2000000  
             Min Echo interval: 250000 - Authentication bit: 0  
Hosting LC: 1, Down reason: None, Reason not-hosted: None

Related Documents

Related Topic

Document Title

BFD commands

Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide

RFCs

RFC

Title

RFC 5880

Bidirectional Forwarding Detection (BFD)

RFC 5881

BFD for IPv4 and IPv6 (Single Hop)

RFC 7130

Bidirectional Forwarding Detection (BFD) on Link Aggregation Group (LAG) Interfaces