Usage Guidelines

When you issue the bfd command in mode, the CLI prompt changes to “config-bfd,” indicating that you have entered BFD configuration mode. In the following sample output, the question mark (? ) online help function displays all the commands available under BFD configuration mode:

Router(config)# bfd
Router(config-bfd)# ?

  commit     Commit the configuration changes to running
  describe   Describe a command without taking real actions
  do         Run an exec command
  echo       Configure BFD echo parameters
  exit       Exit from this submode
  interface  Configure BFD on an interface
  no         Negate a command or set its defaults
  root       Exit to the Router mode
  show       Show contents of configuration
   

Usage Guidelines

This command is supported on bundle interfaces only.

Usage Guidelines

This command is supported on only on BFD over Bundle Per-Member Link Mode using Cisco standard.

This command allows to configure an echo interval to a value greater than async x bfd multiplier value.

Usage Guidelines

This command is supported on bundle interfaces only.

Usage Guidelines

This command is supported on bundle interfaces only.

The BFD minimum interval is used with a configurable multiplier (bfd address-family ipv4 multiplier command) to determine the intervals and failure detection times for both control and echo packets in asynchronous mode on bundle member links.

For example, with a session interval of I and a multiplier of M, the following packet intervals and failure detection times apply for BFD asynchronous mode:

• Value of I—Minimum period between sending of BFD control packets.

• Value of I x M

  • BFD control packet failure detection time. This is the maximum amount of time that can elapse without receipt of a BFD control packet before the session is declared down.

  • Minimum period between sending of BFD echo packets.

• Value of (I x M) x M—BFD echo packet failure detection time. This is the maximum amount of time that can elapse without receipt of a BFD echo packet before the session is declared down.

When used with bundled VLANs, the following restrictions apply:

• The command specifies control packet intervals only because echo packets are not supported.

• The minimum interval is 250 ms.

The bfd address-family ipv4 minimum-interval command in bundle interface configuration overrides the minimum intervals specified by the bfd minimum-interval command in other areas of BFD configuration.

Note	When multiple applications share the same BFD session, the application with the most aggressive timer is used locally. Then, the result is negotiated with the peer router.

Keep the following router-specific rules in mind when configuring the minimum BFD interval:

• The maximum rate in packets-per-second (pps) for BFD sessions is linecard-dependent. If you have multiple linecards supporting BFD, then the maximum rate for BFD sessions per system is the supported linecard rate multiplied by the number of linecards.

• The maximum number of all BFD sessions on the router is 1024.

• The maximum number of all BFD sessions on the router is 1440.

To calculate the rate for BFD sessions on bundle members running in asynchronous mode without echo:

• Divide 1000 by the value of the minimum interval (as specified by the bfd address-family ipv4 minimum-interval command). This is also the base rate used per member session with echo:

  Asynchronous rate per bundle member = (1000 / Min-interval)

To calculate the rate for BFD sessions on bundle members running in asynchronous mode with echo:

• Determine the echo interval, which is the value of the minimum interval (specified by the bfd address-family ipv4 minimum-interval command) multiplied by the multiplier value (specified by the bfd address-family ipv4 multiplier command).

  Echo interval = (Min-interval x Multiplier)

• Calculate the overall rate supported for all members on the bundle:

  Ethernet bundle rate = (1000 / Echo interval) x 64

• Add the asynchronous base rate per bundle member to find the total rate for all bundle links:

  Total bundle rate = Ethernet bundle rate + (Base asynchronous rate x Number of links)

Usage Guidelines

This command is supported on bundle interfaces only.

The BFD multiplier is used with a configurable minimum interval (bfd address-family ipv4 minimum-interval command) to determine the intervals and failure detection times for both control and echo packets in asynchronous mode on bundle member links.

For example, with a session interval of I and a multiplier of M, the following packet intervals and failure detection times apply for BFD asynchronous mode:

• Value of I—Minimum period between sending of BFD control packets.

• Value of I x M

  • BFD control packet failure detection time. This is the maximum amount of time that can elapse without receipt of a BFD control packet before the session is declared down.

  • Minimum period between sending of BFD echo packets.

  Note	The maximum echo packet interval for BFD on bundle member links is the minimum of either 30 seconds or the asynchronous control packet failure detection time.

• Value of (I x M) x M—BFD echo packet failure detection time. This is the maximum amount of time that can elapse without receipt of a BFD echo packet before the session is declared down.

Keep the following router-specific rules in mind when configuring the minimum BFD interval:

• The maximum rate in packets-per-second (pps) for BFD sessions is linecard-dependent. If you have multiple linecards supporting BFD, then the maximum rate for BFD sessions per system is the supported linecard rate multiplied by the number of linecards.

• The maximum number of all BFD sessions per linecard is 1024.

• The maximum number of all BFD sessions per linecard is 1440.

To calculate the rate for BFD sessions on bundle members running in asynchronous mode without echo:

• Divide 1000 by the value of the minimum interval (as specified by the bfd address-family ipv4 minimum-interval command). This is also the base rate used per member session with echo:

  Asynchronous rate per bundle member = (1000 / Min-interval)

To calculate the rate for BFD sessions on bundle members running in asynchronous mode with echo:

• Determine the echo interval, which is the value of the minimum interval (specified by the bfd address-family ipv4 minimum-interval command) multiplied by the multiplier value (specified by the bfd address-family ipv4 multiplier command).

  Echo interval = (Min-interval x Multiplier)

• Calculate the overall rate supported for all members on the bundle:

  Ethernet bundle rate = (1000 / Echo interval) x 64

• Add the asynchronous base rate per bundle member to find the total rate for all bundle links:

  Total bundle rate = Ethernet bundle rate + (Base asynchronous rate x Number of links)

Usage Guidelines

This command is supported on bundle interfaces only.

Usage Guidelines

The default behavior for BLB without any coexistence configuration behaves exactly as the BVLAN configuration.

When the "inherited" coexistence mode is configured, the BLB session always uses the inherited mode. It always creates a virtual session, and never a BFD session with real packets. This mode prevents the automatic conversion between BLB and the inherited mode, which could happen in default mode, depending on the sequence in which the configuration is applied. The "inherited" session is in "Down" state when BoB is not enabled.

The "logical" mode always creates BFD session with real packets.

Usage Guidelines

Note	The initial-wait, maximum-wait, and secondary-wait keywords are dampening timers.

You do not have to configure the BFD startup timers. If you do configure the initial wait startup timer (using the initial-wait keyword), then it must be less than the value of the maximum-wait timer.

You do not have to configure the BFD startup timers. If you do configure the initial wait startup timer (using the initial-wait keyword), then it must be less than the value of the maximum-wait timer.

By default, BFD dampening is applied to all sessions in the following manner:

• If a session is brought down, then dampening is applied before a session is allowed to transition to initial/up states.

• Length of time a session is dampened grows exponentially with continuous session flap.

• If a session remains up for minimum two minutes, then the length of time a session dampens with the next session flap is reset to the initial dampening value.

BFD on bundle member applies dampening, only if the detected failure is specific to layer 3. BFD dampening is not invoked for L1 or L2 failures. BFD is started after Layer 1 and Layer 2 (LACP) is up to prevent a race condition and false triggers. BFD is notified to stop/ignore when L1 or L2 goes down and must be notified to start/resume when L1 or L2 recovers for a given/affected link/member.

BFD applies dampening till the session transitions from up to down state and the session is not removed. Whenever there is a failure detected at L1 or L2 , the bundle manager removes BFD session on a member.

When dampening is removed a syslog message ‘Exponential backoff dampening for BFD session has been cleared for specified BFD session. When/if same session gets created by application(s), only calculated initial wait time will be applied’ is generated. If this is the desired behavior, then dampening can be enabled by configuring the BFD configuration, by using the command bfd dampening bundle-member l3-failure-only .

Usage Guidelines

Note	BFD can support multihop for internal and external BGP peers.

Use the bfd fast-detect command to provide protocol- and media-independent, short-duration failure detection of the path between adjacent forwarding engines, including the interfaces and data links.

BFD must be configured on directly connected neighbors for a BFD session to be established between the neighbors.

In OSPF and OSPF3 environments, the setting of the bfd fast-detect command is inherited from the highest-level configuration mode in which the command was configured. From the lowest to the highest configuration modes, the inheritance rules are as follows:

• If you enable BFD in area interface configuration mode, it is enabled on the specified interface only.

• If you enable BFD in area configuration mode, it is enabled on all interfaces in the specified area.

• If you enable BFD in router configuration mode, it is enabled on all areas and all associated interfaces in the specified routing process.

In OSPF environments, the disable option enables you to override the inheritance rules described previously. For example, if you enable BFD in an OSPF area, BFD is enabled on all interfaces in that area. If you do not want BFD running on one of the interfaces in that area, you must specify the bfd fast-detect disable command for that interface only.

To disable BFD or return the software to the default state in which BFD is not enabled in IS-IS router configuration mode, you must enter the no bfd fast-detect command.

Usage Guidelines

In OSPF environments, the setting of the bfd minimum-interval command is inherited from the highest-level configuration mode in which the command was configured. From the lowest to the highest configuration modes, the inheritance rules are as follows:

• If you configure the minimum interval in area interface configuration mode, the updated interval affects the BFD sessions on the specified interface only.

• If you configure the minimum interval in area configuration mode, the updated interval affects the BFD sessions on all interfaces in the specified area.

If desired, you can override these inheritance rules by explicitly configuring the bfd minimum-interval command for a specific area interface or area.

Note	When multiple applications share the same BFD session, the application with the most aggressive timer wins locally. Then, the result is negotiated with the peer router.

Keep the following router-specific rules in mind when configuring the minimum BFD interval:

• The maximum rate in packets-per-second (pps) for BFD sessions is linecard-dependent. If you have multiple linecards supporting BFD, then the maximum rate for BFD sessions per system is the supported linecard rate multiplied by the number of linecards.

• If a session is running in asynchronous mode without echo, then PPS used for this session is (1000 / asynchronous interval in milliseconds).

• If a session is running in asynchronous mode with echo, then PPS used for this session is (1000 / echo interval in milliseconds).

  This is calculated as: 1000 / value of the bfd minimum-interval command.

• The table below defines the maximum number of BFD sessions that is allowed per line card.

  Table 1. Supported Scale

  Timer Value	Maximum Number of Sessions Supported in a line card.	Maximum Number of Sessions Supported in a system.
  300 ms	250	500
  1 second	250	500
  2 seconds	250	500

Usage Guidelines

If the BFD mode is configured when the bundle is being created, the configuration goes through. This is because, both the BFD state as well as the bundle state are 'down' during bundle creation. To apply the mode change for existing sessions, bring down and then recreate the BFD sessions for that bundle.

A BFD session on the member interfaces can belong to only one mode (Cisco or IETF mode). Mix of the modes within the same bundle is not supported. This command is supported on bundle interfaces only.

Usage Guidelines

In OSPF environments, the setting of the bfd multiplier command is inherited from the highest-level configuration mode in which the command was configured. From the lowest to the highest configuration modes, the inheritance rules are as follows:

• If you configure a multiplier in area interface configuration mode, the updated multiplier affects the BFD sessions on the specified interface only.

• If you configure a multiplier in area configuration mode, the updated multiplier affects the BFD sessions on all interfaces in the specified area.

• If you configure a multiplier in router configuration mode, the updated multiplier affects the BFD sessions in all areas and all associated interfaces in the specified routing process.

If desired, you can override these inheritance rules by explicitly configuring the bfd multiplier command for a specific area interface or area.

If the multiplier is changed using the bfd multiplier command, the new value is used to update all existing BFD sessions for the protocol.

Usage Guidelines

For the interface-path-id argument, use the following guidelines:

• If specifying a physical interface, the naming notation is rack/slot/module/port. The slash between values is required as part of the notation. An explanation of each component of the naming notation is as follows:

  • rack: Chassis number of the rack.

  • slot: Physical slot number of the line card.

  • module: Module number. A physical layer interface module (PLIM) is always 0.

  • port: Physical port number of the interface.

• If specifying a virtual interface, the number range varies, depending on interface type.

Usage Guidelines

For the interface-path-id argument, use the following guidelines:

• If specifying a physical interface, the naming notation is rack/slot/module/port. The slash between values is required as part of the notation. An explanation of each component of the naming notation is as follows:

  • rack: Chassis number of the rack.

  • slot: Physical slot number of the line card.

  • module: Module number. A physical layer interface module (PLIM) is always 0.

  • port: Physical port number of the interface.

• If specifying a virtual interface, the number range varies, depending on interface type.

Usage Guidelines

If you are using BFD with Unicast Reverse Path Forwarding (uRPF), you need to use the echo disable command to disable echo mode; otherwise, echo packets are rejected.

Note	To enable or disable IPv4 uRPF checking on an IPv4 interface, use the [no] ipv4 verify unicast source reachable-via command in interface configuration mode.

Usage Guidelines

For the interface-path-id argument, use the following guidelines:

• If specifying a physical interface, the naming notation is rack/slot/module/port. The slash between values is required as part of the notation. An explanation of each component of the naming notation is as follows:

  • rack: Chassis number of the rack.

  • slot: Physical slot number of the line card.

  • module: Module number. A physical layer interface module (PLIM) is always 0.

  • port: Physical port number of the interface.

• If specifying a virtual interface, the number range varies, depending on interface type.

If you are using BFD with Unicast Reverse Path Forwarding (uRPF) on a particular interface, then you need to use the echo disable command in BFD interface configuration mode to disable echo mode on that interface; otherwise, echo packets are rejected by the interface.

Note	To enable or disable IPv4 uRPF checking on an IPv4 interface, use the [no] ipv4 verify unicast source reachable-via command in interface configuration mode.

Usage Guidelines

For the interface-path-id argument, use the following guidelines:

• If specifying a physical interface, the naming notation is rack/slot/module/port. The slash between values is required as part of the notation. An explanation of each component of the naming notation is as follows:

  • rack: Chassis number of the rack.

  • slot: Physical slot number of the line card.

  • module: Module number. A physical layer interface module (PLIM) is always 0.

  • port: Physical port number of the interface.

• If specifying a virtual interface, the number range varies, depending on interface type.

Usage Guidelines

When node-id is not specified, information for all IPv4 and IPv6 BFD MIB sessions, stored on the route processor node, is displayed, and this information is populated and updated only after SNMP operations for those BFD MIB sessions are performed.

When node-id is specified, information for all IPv4 and IPv6 BFD MIB sessions, stored on the specified node (linecard), is displayed, and this information is updated automatically without SNMP operations being performed.

Usage Guidelines

No specific guidelines impact the use of this command.

Usage Guidelines

For the interface-path-id argument, use the following guidelines:

• If specifying a physical interface, the naming notation is rack/slot/module/port. The slash between values is required as part of the notation. An explanation of each component of the naming notation is as follows:

  • rack: Chassis number of the rack.

  • slot: Physical slot number of the line card.

  • module: Module number. A physical layer interface module (PLIM) is always 0.

  • port: Physical port number of the interface.

• If specifying a virtual interface, the number range varies, depending on interface type.

Usage Guidelines

No specific guidelines impact the use of this command.