Implementing BFD

Bidirectional forwarding detection (BFD) provides low-overhead, short-duration detection of failures in the path between adjacent forwarding engines. BFD allows a single mechanism to be used for failure detection over any media and at any protocol layer, with a wide range of detection times and overhead. The fast detection of failures provides immediate reaction to failure in the event of a failed link or neighbor.

Prerequisites for Implementing BFD

You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

The following prerequisites are required to implement BFD:

  • If enabling BFD on Multiprotocol Label Switching (MPLS), an installed composite PIE file including the MPLS package, or a composite-package image is required. For Border Gateway Protocol (BGP), Intermediate System-to-Intermediate System (IS-IS), Static, and Open Shortest Path First (OSPF), an installed Cisco IOS XR IP Unicast Routing Core Bundle image is required.

  • Interior Gateway Protocol (IGP) is activated on the router if you are using IS-IS or OSPF.

  • To enable BFD for a neighbor, the neighbor router must support BFD.

  • To support BFD on bundle member links, be sure that the following requirements are met:

    • The routers on either end of the bundle are connected back-to-back without a Layer 2 switch in between.

    • For a BFD session to start, any one of the following configurations or states are present on the bundle member:

      Link Aggregation Control Protocol (LACP) Distributing state is reached, –Or–

      EtherChannel is configured.

      Hot Standby and LACP Collecting state is reached.

Restrictions for Implementing BFD

These restrictions apply to BFD:

  • Demand mode is not supported in Cisco IOS XR software.

  • Echo latency detection and echo validation are not supported on bundle interfaces.

  • Echo mode is not supported on BFD over bundle interfaces and on bundle VLANS, which is BFD over logical bundle (BLB).

Information About BFD

BFD Packet Intervals on Physical Interfaces

When BFD is running over physical interfaces, echo mode is used only if the configured interval is less than two seconds.

BFD sessions running over physical interfaces when echo mode is enabled send BFD control packets at a slow rate of every two seconds. There is no need to duplicate control packet failure detection at a fast rate because BFD echo packets are already being sent at fast rates and link failures will be detected when echo packets are not received within the echo failure detection time.

Control Packet Failure Detection In Asynchronous Mode

Control packet failure in asynchronous mode without echo is detected using the values of the minimum interval (bfd minimum-interval for non-bundle interfaces, and bfd address-family ipv4 minimum-interval for bundle interfaces) and multiplier (bfd multiplier for non-bundle interfaces, and bfd address-family ipv4 multiplier for bundle interfaces) commands.

For control packet failure detection, the local multiplier value is sent to the neighbor. A failure detection timer is started based on (I x M), where I is the negotiated interval, and M is the multiplier provided by the remote end.

Whenever a valid control packet is received from the neighbor, the failure detection timer is reset. If a valid control packet is not received from the neighbor within the time period (I x M), then the failure detection timer is triggered, and the neighbor is declared down.

Priority Settings for BFD Packets

For all interfaces under over-subscription, the internal priority needs to be assigned to remote BFD Echo packets, so that these BFD packets are not overwhelmed by other data packets. In addition, CoS values need to be set appropriately, so that in the event of an intermediate switch, the reply back of remote BFD Echo packets are protected from all other packets in the switch.

As configured CoS values in ethernet headers may not be retained in Echo messages, CoS values must be explicitly configured in the appropriate egress QoS service policy. CoS values for BFD packets attached to a traffic class can be set using the set cos command. For more information on configuring class-based unconditional packet marking, see “Configuring Modular QoS Packet Classification” in the .

BFD over Bundles IETF Mode Support on a Per Bundle Basis

BFD over Bundle (BoB) mode is a standard based fast failure detection of link aggregation (LAG) member links that is interoperable between different platforms. BoB support on a per bundle basis provides an option to choose IETF standard per bundle, without necessitating reloads or process restarts across various systems. .

  • IETF mode uses IANA assigned MAC.

  • IETF BFD over Bundle sessions use destination UDP port: 6784.

Restrictions

These limitations apply for the BFD over Bundle Mode feature:

  • You can use the no bfd address-family ipv4 fast-detect command to make BoB non-operational. You can also choose to configure a bundle to 'down' state by configuring shutdown under that particular bundle.

  • For a bundle to accept the new BFD mode change, you must bring down and then recreate the existing BFD sessions.

BFD Dampening

Bidirectional Forwarding Detection (BFD) is a mechanism used by routing protocols to quickly realize and communicate the reachability failures to their neighbors. When BFD detects a reachability status change of a client, its neighbors are notified immediately. Sometimes it might be critical to minimize changes in routing tables so as not to impact convergence, in case of a micro failure. An unstable link that flaps excessively can cause other devices in the network to consume substantial processing resources, and that can cause routing protocols to lose synchronization with the state of the flapping link.

The BFD Dampening feature introduces a configurable exponential delay mechanism. This mechanism is designed to suppress the excessive effect of remote node reachability events flapping with BFD. The BFD Dampening feature allows the network operator to automatically dampen a given BFD session to prevent excessive notification to BFD clients, thus preventing unnecessary instability in the network. Dampening the notification to a BFD client suppresses BFD notification until the time the session under monitoring stops flapping and becomes stable.

Configuring the BFD Dampening feature, especially on a high-speed interface with routing clients, improves convergence time and stability throughout the network. BFD dampening can be applied to all types of BFD sessions, including IPv4/single-hop, Multiprotocol Label Switching-Transport Profile (MPLS-TP), and Pseudo Wire (PW) Virtual Circuit Connection Verification (VCCV).

BFD Session Dampening

You can configure the BFD Dampening feature at the BFD template level (single-hop template). Dampening is applied to all the sessions that use the BFD template. If you choose not to have a session to be dampened, you should use a new BFD template without dampening for a new session. By default, the dampening functionality is not enabled on a template.

BFD Hardware Offload Support for IPv4

The Bidirectional Forwarding detection (BFD) Hardware Offload feature enables the offload of a BFD session to the network processing units of the line cards, in an IPv4 network. BFD hardware offload improves scale and reduces the overall network convergence time by sending rapid failure detection packets to the routing protocols for recalculating the routing table.

Restrictions

  • This feature is not supported over MPLS LDP interface, VRRP interface, BVI interface and IRB interface.

Confiugration Example

/* Configure BFD over Bundle(BOB) for hardware offload. */
Router# config
Router(config)# interface Bundle-Ether 1
Router(config-if)# bfd mode ietf
Router(config-if)# bfd address-family ipv4 multiplier 3
Router (config-if)# bfd address-family ipv4 destination 10.20.20.1
Router (config-if)# bfd address-family ipv4 fast-detect 
Router(config-if)# bfd address-family ipv4 minimum-interval 1200
Router(config-if)# ipv4 address 10.20.20.2/30

/* Configure BFD with a static route. */
Router(config)# router static
Router(config-static)# address-family ipv4 unicast 10.1.1.0/24 10.6.0.2 bfd fast-detect minimum-interval 1200 multiplier 4

/* Configure BFD with IS-IS. */
Router(config)# router isis 65444
Router(config-isis)# address-family ipv4 unicast
Router(config-isis)# exit
Router(config-isis)# interface HundredGige 0/3/0/1
Router(config-isis-if)#  bfd minimum-interval 1200
Router(config-isis-if)# bfd multiplier 7
Router(config-isis-if)# bfd fast-detect ipv4
Router(config-isis-if)# address-family ipv4 unicast

/* Configure BFDv4 with OSPF. */
Router(config)# router ospf main
Router(config-ospfv3)# area 0
Router(config-ospfv3-ar)#  interface HundredGige 0/0/0/1
Router(config-ospfv3-ar-if)# bfd multiplier 7
Router(config-ospfv3-ar-if)# bfd fast-detect
Router(config-ospfv3-ar-if)# bfd minimum-interval 1200

/* Configuring BFD over BGP. */
Router(config)# router bgp 120
Router(config-bgp)# neighbor 10.6.6.1
Router(config-bgp-nbr)# bfd fast-detect
Router(config-bgp-nbr)# bfd multiplier 7
Router(config-bgp-nbr)# bfd minimum-interval 1200

Verification

Use the show bfd ipv4 session command to verify the configuration: 

Router# show bfd ipv4 session
Interface           Dest Addr           Local det time(int*mult)       State     
                                    Echo             Async   H/W       NPU     
------------------- --------------- ---------------- ---------------- ----------
Hu0/0/0/22.93       10.20.20.1       0s(0s*0)         12ms(4ms*3)      UP        
                                                             Yes   0/0/CPU0

BFD Hardware Offload Support for IPv6

The Bidirectional Forwarding detection (BFD) Hardware Offload feature enables the offload of a BFD session to the network processing units of the line cards, in an IPv6 network. BFD hardware offload feature improves scale and reduces the overall network convergence time by sending rapid failure detection packets to the routing protocols for recalculating the routing table.

Restrictions

  • This feature is not supported over MPLS LDP interface, VRRP interface, BVI interface and IRB interface.

  • BFD Dampening is not supported for BFD over IPv6.

  • BFD over Bundle (BOB) over IPv6 is not supported with dynamically configured link-local address. It must be statically configured.

Configuration Example

/* Configure BFD over Bundle(BOB) for hardware offload. */
Router# config
Router(config)# interface Bundle-Ether 1
Router(config-if)# bfd mode ietf
Router(config-if)# bfd address-family ipv6 multiplier 3
Router (config-if)# bfd address-family ipv6 destination 10.20:20::1
Router (config-if)# bfd address-family ipv6 fast-detect 
Router(config-if)# bfd address-family ipv6 minimum-interval 1200
Router(config-if)# ipv6 address 10:20:20::2/64

/* Configure BFD with a static route. */
Router(config)# router static
Router(config-static)# address-family ipv6 unicast 1011:17e4::1/128 ab11:15d2::2 bfd fast-detect minimum-interval 1200 multiplier 3

/* Configure BFD with IS-IS. */
Router(config)# router isis 65444
Router(config-isis)# address-family ipv6 unicast
Router(config-isis)# exit
Router(config-isis)# interface HundredGige 0/3/0/1
Router(config-isis-if)#  bfd minimum-interval 1200
Router(config-isis-if)# bfd multiplier 7
Router(config-isis-if)# bfd fast-detect ipv6
Router(config-isis-if)# address-family ipv6 unicast

/* Configure BFDv6 with OSPFv3. */
Router(config)# router ospfv3 main
Router(config-ospfv3)# area 0
Router(config-ospfv3-ar)#  interface HundredGige 0/0/0/1
Router(config-ospfv3-ar-if)# bfd multiplier 7
Router(config-ospfv3-ar-if)# bfd fast-detect
Router(config-ospfv3-ar-if)# bfd minimum-interval 1200

/* Configuring BFD over BGP. */
Router(config)# router bgp 120
Router(config-bgp)# neighbor 2001:DB8:1::1
Router(config-bgp-nbr)# bfd fast-detect
Router(config-bgp-nbr)# bfd multiplier 7
Router(config-bgp-nbr)# bfd minimum-interval 1200

Verification

Use the show bfd ipv6 session command to verify the configuration: 

Router# show bfd ipv6 session
Interface           Dest Addr      
                                        Local det time(int*mult)      State     
H/W                 NPU             Echo             Async           
------------------- --------------- ---------------- ---------------- ----------
BE7.2               fe80::28a:96ff:fed6:9cdb                      
Yes                 0/0/CPU0        0s(0s*0)         900ms(300ms*3)   UP        
BE7.4               fe80::28a:96ff:fed6:9cdb                      
Yes                 0/0/CPU0        0s(0s*0)         900ms(300ms*3)   UP

IPv4 Multihop BFD

IPv4 Multihop BFD is a BFD session between two addresses between two nodes. An example of this feature is a BFD session between PE and CE loopback addresses or BFD sessions between routers that are several TTL hops away. The applications that support IPv4 Multihop BFD are external and internal BGP. IPv4 Multihop BFD feature supports BFD on arbitrary paths, which can span multiple network hops.

The IPv4 Multihop BFD feature provides sub-second forwarding failure detection for a destination more than one hop, and up to 255 hops, away. The bfd multihop ttl-drop-threshold command can be used to drop BFD packets coming from neighbors exceeding a certain number of hops.

Configure IPv4 Multihop BFD

This section describes how you can configure IPv4 Multihop BFD feature.

Router# configure
Router(config)# bfd
Router(config)# multihop ttl-drop-threshold 225
Router(config)# multipath include location 0/7/CPU0
Router(config)# router bgp 100
Router(config-bgp)# neighbor 209.165.200.225
Router(config-bgp-nbr)# remote-as 2000
Router(config-bgp-nbr)# update-source loopback 1
Router(config-bgp-nbr)# bfd fast-detect
Router(config-bgp-nbr)# bfd multiplier 3
Router(config-bgp-nbr)# bfd minimum-interval 1200
Router(config-bgp-nbr-af)# route-policy pass-all in
Router(config-bgp-nbr-af)# route-policy pass-all out
Router(config-bgp-nbr-af)# commit

Running Configuration


bfd
 multihop ttl-drop-threshold 225
 multipath include location 0/7/CPU0
router bgp 100
 neighbor 209.165.200.225
  remote-as 2000
  update-source loopback 1
  bfd fast-detect
  bfd multiplier 3
  bfd minimum-interval 1200
      route-policy PASS-ALL in
    route-policy PASS-ALL out
  !
!

Verification

The show outputs given in the following section display the details of the configuration of the IPv4 Multihop BFD feature, and the status of their configuration. 

Router# show tech-support bfdhwoff 
harddisk: 
Tue Mar 20 11:20:29.214 PDT
++ Show tech start time: 2018-Mar-20.112029.PDT ++
Tue Mar 20 11:20:30 PDT 2018 Waiting for gathering to complete .............................
Tue Mar 20 11:22:37 PDT 2018 Compressing show tech output Show tech output available at 0/RP0/CPU0 :
/harddisk:/showtech-bfd-hwoff-platform-2018-Mar-20.112029.PDT.tgz
++ Show tech end time: 2018-Mar-20.112237.PDT ++

Configure BFD

Configure BFD Under a Dynamic Routing Protocol or Use a Static Route

To establish a BFD neighbor, complete at least one of the following procedures to configure BFD under a dynamic routing protocol or to use a static route:

Enabling BFD on a BGP Neighbor

BFD can be enabled per neighbor, or per interface. This task describes how to enable BFD for BGP on a neighbor router.

Procedure

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

router bgp autonomous-system-number

Example:

RP/0/RP0/CPU0:router(config)# router bgp 120

Enters BGP configuration mode, allowing you to configure the BGP routing process.

Step 3

neighbor ip-address

Example:

RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.

This example configures the IP address 172.168.40.24 as a BGP peer.

Step 4

remote-as autonomous-system-number

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002

Creates a neighbor and assigns it a remote autonomous system.

This example configures the remote autonomous system to be 2002.

Step 5

bfd fast-detect

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# bfd fast-detect

Enables BFD between the local networking devices and the neighbor whose IP address you configured to be a BGP peer in Step 3.

In the example in Step 3, the IP address 172.168.40.24 was set up as the BGP peer. In this example, BFD is enabled between the local networking devices and the neighbor 172.168.40.24.

Step 6

bfd minimum-interval milliseconds

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# bfd minimum-interval 1200

Sets the BFD minimum interval. Range is 3-1200 milliseconds.

Step 7

bfd multiplier multiplier

Example:

RP/0/RP0/CPU0:router(config-bgp-nbr)# bfd multiplier 7

Sets the BFD multiplier. This is optional, the minimum is 3 and by default the multiplier will be 3 for all protocols

Step 8

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Enabling BFD for OSPF on an Interface

Perform the following steps to configure BFD for Open Shortest Path First (OSPF) on an interface. The steps in the procedure are common to the steps for configuring BFD on IS-IS; only the command mode differs.


Note

BFD per interface configuration is supported for OSPF and IS-IS only. 


Router# configure

/* Enter OSPF configuration mode to configure the OSPF routing process. */
Router(config)# router ospf 0

/* Set the BFD minimum interval. The range is from 3 to 1200 milliseconds. */
Router(config-ospf)# bfd minimum-interval 1200

/* Set the BFD multiplier. */
Router(config-ospf)# bfd multiplier 7

/* Configure an Open Shortest Path First (OSPF) area. */
Router(config-ospf)# area 0

/* Enter interface configuration mode. */
Router(config-ospf-ar)# interface HundredGige 0/3/0/1

/* Enable BFD to detect failures in the path between adjacent forwarding engines. */
Router(config-ospf-ar-if)# bfd fast-detect
Running Configuration

configure 
  router ospf 0
  bfd minimum-interval 1200
  bfd multiplier 7
   area 0
    interface HundredGige 0/3/0/1
     bfd fast-detect
Verification
Verify that BFD is enabled on the appropriate interface. 
Router(config-ospf-ar-if)# show run router ospf

 router ospf 0
 bfd minimum-interval 1200
 bfd multiplier 7
 area 0
 interface HundredGige 0/3/0/1
 bfd fast-detect

Enabling BFD on a Static Route

The following procedure describes how to enable BFD on a static route. 

Router(config)# configure

/*Enter static route configuration mode, and configure static routing. */
Router(config)# router static

/*Enter address family configuration mode. */
Router(config-static)# address-family ipv4 unicast 192.168.2.2/32 

/*Specify an unicast destination address and next-hop IPv4 address. 
Enable BFD fast-detection on the specified IPv4 unicast destination address */
Router(config-static)# 192.168.2.2 192.168.6.2 bfd fast-detect minimum-interval 1200 multiplier 3
Running Configuration
router static
 address-family ipv4 unicast
  192.168.2.2 192.168.6.2 bfd fast-detect minimum-interval 1200 multiplier 3
 ! 
!

Specifying the BFD Destination Address on a Bundle

To specify the BFD destination address on a bundle, complete these steps:

Procedure

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

interface Bundle-Ether bundle-id

Example:
RP/0/RP0/CPU0:router(config)# interface Bundle-Ether 1

Enters interface configuration mode for the specified bundle ID.

Step 3

bfd address-family ipv4 destination ip-address

Example:
RP/0/RP0/CPU0:router(config-if)# bfd address-family ipv4 destination 10.20.20.1

Specifies the primary IPv4 address assigned to the bundle interface on a connected remote system, where ip-address is the 32-bit IP address in dotted-decimal format (A.B.C.D).

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Enabling BFD Sessions on Bundle Members

To enable BFD sessions on bundle member links, complete these steps:

SUMMARY STEPS

  1. configure
  2. interface Bundle-Ether bundle-id
  3. bfd address-family ipv4 fast-detect
  4. Use the commit or end command.

DETAILED STEPS

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

interface Bundle-Ether bundle-id

Example:
Router(config)# interface Bundle-Ether 1

Enters interface configuration mode for the specified bundle ID.

Step 3

bfd address-family ipv4 fast-detect

Example:
Router(config-if)# bfd address-family ipv4 fast-detect

Enables IPv4 BFD sessions on bundle member links.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Configuring the Minimum Thresholds for Maintaining an Active Bundle

The bundle manager uses two configurable minimum thresholds to determine whether a bundle can be brought up or remain up, or is down, based on the state of its member links.

  • Minimum active number of links

  • Minimum active bandwidth available

Whenever the state of a member changes, the bundle manager determines whether the number of active members or available bandwidth is less than the minimum. If so, then the bundle is placed, or remains, in DOWN state. Once the number of active links or available bandwidth reaches one of the minimum thresholds, then the bundle returns to the UP state.

To configure minimum bundle thresholds, complete these steps:

Procedure

Step 1

configure

Step 2

interface Bundle-Ether bundle-id

Example:
RP/0/RP0/CPU0:router(config)# interface Bundle-Ether 1

Enters interface configuration mode for the specified bundle ID.

Step 3

bundle minimum-active bandwidth kbps

Example:
RP/0/RP0/CPU0:router(config-if)# bundle minimum-active bandwidth 580000

Sets the minimum amount of bandwidth required before a bundle can be brought up or remain up. The range is from 1 through a number that varies depending on the platform and the bundle type.

Step 4

bundle minimum-active links links

Example:
RP/0/RP0/CPU0:router(config-if)# bundle minimum-active links 2

Sets the number of active links required before a bundle can be brought up or remain up. The range is from 1 to 32.

Note

 
When BFD is started on a bundle that is already active, the BFD state of the bundle is declared when the BFD state of all the existing active members is known.

Step 5

commit

Configuring BFD Packet Transmission Intervals and Failure Detection Times on a Bundle

BFD asynchronous packet intervals and failure detection times for BFD sessions on bundle member links are configured using a combination of the bfd address-family ipv4 minimum-interval and bfd address-family ipv4 multiplier interface configuration commands on a bundle.

The BFD control packet interval is configured directly using the bfd address-family ipv4 minimum-interval command. The failure detection times are determined by a combination of the interval and multiplier values in these commands.

To configure the minimum transmission interval and failure detection times for BFD asynchronous mode control packets on bundle member links, complete these steps:

Procedure

Step 1

configure

Step 2

interface Bundle-Ether bundle-id

Example:
RP/0/RP0/CPU0:router(config)# interface Bundle-Ether 1

Enters interface configuration mode for the specified bundle ID.

Step 3

bfd address-family ipv4 minimum-interval milliseconds

Example:
RP/0/RP0/CPU0:router(config-if)#bfd address-family ipv4 minimum-interval 1200

Note

 
Specifies the minimum interval, in milliseconds, for asynchronous mode control packets on IPv4 BFD sessions on bundle member links. The range is from 3 to 1200.

Step 4

bfd address-family ipv4 multiplier multiplier

Example:
RP/0/RP0/CPU0:router(config-if)#bfd address-family ipv4 multiplier 30

Specifies a number that is used as a multiplier with the minimum interval to determine BFD control packet failure detection times and transmission intervals for IPv4 BFD sessions on bundle member links.

Note

 
Although the command allows you to configure a minimum of 2, the supported minimum is 3.

Step 5

commit

Configure BFD over Bundles IETF Mode Support on a Per Bundle Basis

To configure BFD over Bundles IETF mode support on a per bundle basis use these steps:

Procedure

Step 1

configure

Step 2

interface Bundle-Ether bundle-id

Example:
RP/0/RP0/CPU0:router(config)# interface Bundle-Ether 1

Enters interface configuration mode for the specified bundle ID.

Step 3

bfd mode ietf

Example:
RP/0/RP0/CPU0:router(config-if)# bfd mode ietf

Enables IETF mode for BFD over bundle for the specified bundle.

Step 4

bfd address-family ipv4 fast-detect

Example:
RP/0/RP0/CPU0:router(config-if)# bfd address-family ipv4 fast-detect

Enables IPv4 BFD sessions on the specified bundle.

Step 5

commit

Step 6

show bundle bundle-ether bundle-id

Displays the selected bundle mode.

Enabling Echo Mode to Test the Forwarding Path to a BFD Peer

BFD echo mode is enabled by default for IPv4 on other physical interfaces whose minimum interval is less than three seconds.

If you have configured a BFD minimum interval greater than three seconds on a physical interface using the bfd minimum-interval command, then you will need to change the interval to be less than three seconds to support and enable echo mode. This does not apply to bundle member links, which always support echo mode.

Overriding the Default Echo Packet Source Address

If you do not specify an echo packet source address, then BFD uses the IP address of the output interface as the default source address for an echo packet.

You can use the echo ipv4 source command in BFD or interface BFD configuration mode to specify the IP address that you want to use as the echo packet source address.

You can override the default IP source address for echo packets for BFD on the entire router, or for a particular interface.

Specifying the Echo Packet Source Address Globally for BFD

To specify the echo packet source IP address globally for BFD on the router, complete the following steps:

Procedure

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

bfd

Example:

Router(config)# bfd

Enters BFD configuration mode.

Step 3

echo ipv4 source ip-address

Example:

Router(config-bfd)# echo ipv4 source 10.10.10.1

Specifies an IPv4 address to be used as the source address in BFD echo packets, where ip-address is the 32-bit IP address in dotted-decimal format (A.B.C.D).

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Specifying the Echo Packet Source Address on an Individual Interface

To specify the echo packet source IP address on an individual BFD interface, complete the following steps:

Procedure

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

bfd

Example:

Router(config)# bfd

Enters BFD configuration mode.

Step 3

interface type interface-path-id

Example:

Router(config-bfd)# interface HundredGige 0/1/5/0

Enters BFD interface configuration mode for a specific interface. In BFD interface configuration mode, you can specify an IPv4 address on an individual interface.

Step 4

echo ipv4 source ip-address

Example:

Router(config-bfd)# echo ipv4 source 10.10.10.1

Specifies an IPv4 address to be used as the source address in BFD echo packets, where ip-address is the 32-bit IP address in dotted-decimal format (A.B.C.D).

Step 5

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Disabling Echo Mode

BFD does not support asynchronous operation in echo mode in certain environments.

You can disable echo mode for BFD on the entire router, or for a particular interface.

Disabling Echo Mode on a Router

To disable echo mode globally on the router complete the following steps:

DETAILED STEPS
Procedure

Step 1

configure

Step 2

bfd

Example:

Router(config)# bfd

Enters BFD configuration mode.

Step 3

echo disable

Example:

Router(config-bfd)# echo disable

Disables echo mode on the router.

Step 4

commit

Disabling Echo Mode on an Individual Interface

The following procedures describe how to disable echo mode on an interface.

Procedure

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

bfd

Example:

Router(config)# bfd

Enters BFD configuration mode.

Step 3

interface type interface-path-id

Example:

Router(config-bfd)# interface HundredGige 0/1/5/0

Enters BFD interface configuration mode for a specific interface. In BFD interface configuration mode, you can disable echo mode on an individual interface.

Step 4

echo disable

Example:

Router(config-bfd-if)# echo disable

Disables echo mode on the specified individual interface.

Step 5

commit

Minimizing BFD Session Flapping Using BFD Dampening

To configure BFD dampening to control BFD session flapping, complete the following steps.

Procedure

Step 1

configure

Example:

RP/0/# configure

Enters mode.

Step 2

bfd

Example:

Router(config)# bfd

Enters BFD configuration mode.

Step 3

dampening [bundle-member] {initial-wait | maximum-wait | secondary-wait} milliseconds

Example:

Router(config-bfd)# dampening initial-wait 30000

Specifies delays in milliseconds for BFD session startup to control flapping.

The value for maximum-wait should be greater than the value for initial-wait .

The dampening values can be defined for bundle member interfaces and for the non-bundle interfaces.

Step 4

Use the commit or end command.

commit —Saves the configuration changes and remains within the configuration session.

end —Prompts user to take one of these actions:

  • Yes — Saves configuration changes and exits the configuration session.

  • No —Exits the configuration session without committing the configuration changes.

  • Cancel —Remains in the configuration session, without committing the configuration changes.

Clear and Display BFD Counters

The following procedure describes how to display and clear BFD packet counters. You can clear packet counters for BFD sessions that are hosted on a specific node or on a specific interface. 


Router# show bfd counters all packet location 0/3/cpu0
Router# clear bfd counters all packet location 0/3/cpu0
Router# show bfd counters all packet location 0/3/cpu0

BFD IPv6 in Bundle Manager Domain

A configuration to enable or disable BFD to run over a bundle interface can be in the bundle manager domain. The bundle manager can apply these configuration changes, and based on the configuration changes, request the BFD server to enable or disable BFD on certain bundle interfaces and a member links related to those bundle interfaces.

BFD Over BGP: Example

The following example shows how to configure BFD between autonomous system 1200 and neighbor 192.168.70.24:


Router#configure
Router#(config)#router bgp 1200
Router#(config-bgp)#bfd multiplier 2
Router#(config-bgp)#bfd minimum-interval 1200
Router#(config-bgp)#neighbor 192.168.70.24
Router#(config-bgp-nbr)#remote-as 2
Router#(config-bgp-nbr)#bfd fast-detect
Router#(config-bgp-nbr)#commit
Router#(config-bgp-nbr)#end
Router##show run router bgp

BFD Over OSPF: Example

The following example shows how to enable BFD for OSPF on a HundreGigE interface: 


Router#configure
Router#(config)#router ospf 0
Router#(config-ospf)#area 0
Router#(config-ospf-ar)#interface HundredGige 0/3/0/1
Router#(config-ospf-ar-if)#bfd fast-detect
Router#(config-ospf-ar-if)#commit
Router#(config-ospf-ar-if)#end

Router#show run router ospf

router ospf 0
area 0
interface HundredGige 0/3/0/1
bfd fast-detect

BFD Over Static Routes: Example

The following example shows how to enable BFD on an IPv4 static route. In this example, BFD sessions are established with the next-hop 10.3.3.3 when it becomes reachable. 


Router#configure
Router(config)#router static
Router(config-static)#address-family ipv4 unicast
Router(config-static)#10.2.2.0/24 10.3.3.3 bfd fast-detect
Router(config-static)#end

BFD Echo Mode Disable: Examples

The following example shows how to disable echo mode on a router:


Router#configure
Router#(config)#bfd
Router#r(config-bfd)#echo disable

The following example shows how to disable echo mode on an interface:


Router##configure
Router#(config)#bfd
Router#(config-bfd)#interface HundredGige 0/1/0/0
Router#(config-bfd-if)#echo disable

Echo Packet Source Address: Examples

The following example shows how to specify the IP address 10.10.10.1 as the source address for BFD echo packets for all BFD sessions on the router: 


Router#configure
Router(config)#bfd
Router(config-bfd)#echo ipv4 source 10.10.10.1

The following example shows how to specify the IP address 10.10.10.1 as the source address for BFD echo packets on an individual HundredGige Ethernet interface: 


Router#configure
Router(config)#bfd
Router(config-bfd)#interface HundredGige 0/1/0/0
Router(config-bfd-if)#echo ipv4 source 10.10.10.1

BFD Dampening: Examples

The following example shows how to configure an initial and maximum delay for BFD session startup on BFD bundle members:


Router#configure
Router(config)#bfd
Router(config-bfd)#dampening bundle-member initial-wait 8000
Router(config-bfd)#dampening bundle-member maximum-wait 15000

The following example shows how to change the default initial-wait for BFD on a non-bundle interface:


Router#configure
Router(config)#bfd
Router(config-bfd)#dampening initial-wait 30000
Router(config-bfd)#dampening maximum-wait 35000

BFD Hardware Offload for RSVP Tail-End

Table 1. Feature History Table

Feature Name

Release

Description

BFD Hardware Offload for Resource Reservation Protocol Tail-End

Release 7.9.1

You can use Bidirectional Forwarding Detection (BFD) to detect Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) data plane failures.

This feature improves the scale and reduces the overall network convergence time by sending rapid failure detection packets to the routing protocols for recalculating the routing table.

BFD process interacts with the Tail-End and LSPV processes to support BFD over Tail-End LSP feature. MPLS TE automatically establishes and maintains the LSPs across the MPLS network by using the Resource Reservation Protocol (RSVP).

You can use Bidirectional Forwarding Detection (BFD) to detect Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) data plane failures. An LSP ping request is used for detecting MPLS data plane failures and also for verifying the data plane against the control plane. BFD cannot be used for verifying the data plane against the control plane. However, the control plane processing required for BFD control packets is relatively smaller than the processing required for LSP ping messages. Hence, BFD can be deployed for faster detection of data plane failure (for example, traffic black-holing) for a large number of LSPs.

This feature improves the scale and reduces the overall network convergence time by sending rapid failure detection packets to the routing protocols for recalculating the routing table.

BFD over MPLS Traffic Engineering LSPs

Bidirectional Forwarding Detection ( BFD) over MPLS Traffic Engineering Label Switched Paths (LSPs) feature in Cisco IOS XR Software detects MPLS Label Switched Path LSP data plane failures. Since the control plane processing required for BFD control packets is relatively smaller than the processing required for LSP Ping messages, BFD can be deployed for faster detection of data plane failure for a large number of LSPs.

The BFD over MPLS TE LSPs implementation in Cisco IOS XR Software is based on RFC 5884: Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs). LSP Ping is an existing mechanism for detecting MPLS data plane failures and for verifying the MPLS LSP data plane against the control plane. BFD can be used for detecting MPLS data plane failures, but not for verifying the MPLS LSP data plane against the control plane. A combination of LSP Ping and BFD provides faster data plane failure detection on a large number of LSPs.

The BFD over MPLS Tail-End LSPs is used for networks that have deployed MPLS as the multi service transport and that use BFD as fast failure detection mechanism to enhance network reliability and up time by using BFD as fast failure detection traffic black holing.

BFD process interacts with the Tail-End and LSPV processes to support BFD over TE LSP feature. MPLS Tail-End automatically establishes and maintains the LSPs across the MPLS network by using the Resource Reservation Protocol (RSVP).

To know how MPLS works with RSVP Tail-End, refer to the MPLS Configuration guide for Cisco 8000 Routers.

BFD over MPLS Tail-End LSPs support:

  • BFD async mode (BFD echo mode is not supported)

  • IPv4 only, since MPLS core is IPv4

  • BFD packets that carry IP DSCP 6 (Internet Control)

  • Use of BFD for TE tunnel bring up, re-optimization, and path protection (Standby and FRR)

  • Fastest detection time (3 ms x 3 = 9 ms)

  • Optional Periodic LSP ping verification after BFD session is up

  • Dampening to hold-down BFD failed path-option

There are two ways in which the BFD packets from tail-end to head-end will be used:

  • BFD packets from tail-end to head-end will be IP routed

  • BFD packets from tail-end to head-end will be Label Switched if MPLS LDP is available in Core with label path from tail-end to head-end.

Configuring BFD over MPLS Traffic Engineering LSPs

Enabling BFD Parameters for BFD over TE Tunnels

BFD for TE tunnel is enabled at the head-end by configuring BFD parameters under the tunnel. When BFD is enabled on the already up tunnel, TE waits for the bringup timeout before bringing down the tunnel. BFD is disabled on TE tunnels by default. Perform these tasks to configure BFD parameters and enable BFD over TE Tunnels.

Note

BFD paces the creation of BFD sessions by limiting LSP ping messages to be under 50 PPS to avoid variations in CPU usage.

  1. Enter global configuration mode.

    Router#config

  2. Configure MPLS OAM.

    Router(config)# mpls oam

  3. Configure MPLS Traffic Engineering (MPLS TE) tunnel interface and enter into MPLS TE tunnel interface configuration mode.

    Router(config)#interface tunnel-te 65535

  4. Enable BFD fast detection.

    Router(config-if)#bfd fast-detect

  5. Configure hello interval in milliseconds.

    Router(config-if)#bfd minimum-interval 500

    Note

    Hello interval range is 3 to 1000 milliseconds. Default hello interval is 100 milliseconds.

  6. Configure BFD multiplier detection.

    Router(config-if)#bfd multiplier 5

    Note

    BFD multiplier range is 3 to 10. Default BFD multiplier is 3.

  7. Commit the changes. 

    Router(config-if)#commit

Configuring BFD Bring up Timeout

Perform these steps to configure BFD bring up timeout interval.

  1. Enter global configuration mode.

    Router#config

  2. Configure MPLS Traffic Engineering (MPLS TE) tunnel interface and enter into MPLS TE tunnel interface configuration mode.

    Router(config)#interface tunnel-te 65535

  3. Enable the time interval (in seconds) to wait for the BFD session to come up.

    Router(config-if)#bfd bringup-timeout 2400

    Note

    The timeout range is 6 to 3600 seconds. Default bring up timeout interval is 60 seconds.

  4. Commit the changes.

    Router(config-if)#commit

Configuring BFD Dampening for TE Tunnels

When BFD session fails to come up, TE exponentially backs off using the failed path-option to avoid signaling churn in the network. Perform these steps to configure dampening intervals to bring the TE tunnel up.

  1. Enter global configuration mode.

    Router# configure

  2. Configure MPLS Traffic Engineering (MPLS TE) tunnel interface and enter into MPLS TE tunnel interface configuration mode.

    Router(config)#interface tunnel-te 65535

  3. Configure the initial delay interval before bringing up the tunnel.

    Router(config-if)#bfd dampening initial-wait 360000

    Note

    The initial-wait bring up delay time interval range is 1 to 518400000 milliseconds. Default initial-wait interval is 16000 milliseconds.

  4. Configure the maximum delay interval before bringing up the tunnel.

    Router(config-if)#bfd dampening maximum-wait 700000

    Note

    The maximum-wait bring up delay time interval range is 1 to 518400000 milliseconds. Default initial-wait interval is 600000 milliseconds.

  5. Configure the secondary delay interval before bringing up the tunnel.

    Router(config-if)#bfd dampening secondary-wait 30000

    Note

    The secondary-wait bring up delay time interval range is 1 to 518400000 milliseconds. Default secondary-wait interval is 20000 milliseconds.

  6. Commit the changes.

    Router(config-if)#commit

Configuring Periodic LSP Ping Requests

Perform this task to configure sending periodic LSP ping requests with BFD TLV, after BFD session comes up.

  1. Enter global configuration mode.

    Router# configure

  2. Configure MPLS Traffic Engineering (MPLS TE) tunnel interface and enter into MPLS TE tunnel interface configuration mode.

    Router(config)#interface tunnel-te 65535

  3. Set periodic interval for LSP ping requests in seconds.

    Router(config-if)#bfd lsp-ping interval 300

    Note

    The interval range is 60 to 3600 seconds. Default interval is 120 seconds.

  4. Commit the changes.

    Router(config-if)#commit

Configuring BFD at the Tail-End

Use the tail-end global configuration commands to set the BFD minimum-interval and BFD multiplier parameters for all BFD over LSP sessions. The ranges and default values are the same as the BFD head-end configuration values. BFD will take the maximum value set between head-end minimum interval and tail-end minimum interval. Perform these tasks to configure BFD at the tail-end.

  1. Enter global configuration mode.

    Router# configure

  2. Configure MPLS OAM. 

    Router(config)# mpls oam

  3. Configure hello interval in milliseconds.

    Router(config)#mpls traffic-eng bfd lsp tail minimum-interval 500

    Note

    Hello interval range is 3 to 1000 milliseconds. Default hello interval is 100 milliseconds.

  4. Configure BFD multiplier detection.

    Router(config)#mpls traffic-eng bfd lsp tail multiplier 5

    Note

    BFD multiplier detect range is 3 to 10. Default BFD multiplier is 3.

  5. Commit the changes.

    Router(config-if)#commit

Configuring BFD over LSP Sessions on Line Cards

BFD over LSP sessions, both head-end and tail-end, are hosted on line cards with following configuration enabled.


Note

For fixed box and centralized platforms, there are no line cards. Datapath is running on routing processors (RPs) which is where BFD sessions need to be created. On fixed box, the configuration must include the RPs instead of LCs. On centralized platforms, you cannot use RP in the config even though BFD sessions will be running on the RPs. You must include one of the MPAs instead of LC in the configuration.

  1. Enter global configuration mode.

    Router# configure

  2. Enter BFD configuration mode.

    Router(config)# bfd

  3. Configure BFD multiple path on specific line card. 

    Router(config-bfd)# multipath include location 0/1/CPU0

  4. Commit the changes.

    Router(config-if)#commit

BFD over MPLS TE Tunnel Tail-End Configuration

You can use the mpls traffic-eng bfd lsp tail minimum-interval command to configure the tail-end at a minimum interval of 3 milli seconds.

Configuration

Router#config
Router(config)#mpls traffic-eng bfd lsp tail minimum-interval 3
Router(config)#commit

Running Configuration


mpls traffic-eng bfd lsp tail minimum-interval 3
 !

Verification

Use the show bfd session command to verify the configuration on tail-end. 


Router#show bfd session

Src Addr            Dest Addr       VRF Name         Type Specific Data        
                                        Local det time(int*mult)      State     
H/W                 NPU                 Echo             Async           
------------------- --------------- ---------------- ---------------- ----------
1.1.1.1             2.2.2.2         default          TT32768 (LSP:2)           
                                    n/a              1500ms(500ms*3)  UP

Use the show bfd label session to verify the configuration on head-end. 


Router#show bfd label session

Interface           Label               Local det time(int*mult)      State     
                                    Echo             Async           
H/W                 NPU            
------------------- --------------- ---------------- ---------------- ----------
tt1 (LSP:103)       24001           n/a              150ms(50ms*3)    UP        
Yes                 0/1/CPU0       
tt2 (LSP:102)       24002           n/a              150ms(50ms*3)    UP        
Yes                 0/1/CPU0       
tt3 (LSP:101)       24004           n/a              150ms(50ms*3)    UP        
Yes                 0/1/CPU0       
tt4 (LSP:103)       24005           n/a              150ms(50ms*3)    UP        
Yes                 0/1/CPU0       
tt5 (LSP:104)       24006           n/a              150ms(50ms*3)    UP        
Yes                 0/1/CPU0

Configuration Examples for Configuring BFD

BFD over MPLS TE LSPs Examples

These examples explain how to configure BFD over MPLS TE LSPs.

BFD Over MPLS TE Tunnel Head-End Configuration: Example

This example shows how to configure BFD over MPLS TE Tunnel at head-end.

Router# bfd multipath include loc 0/1/CPU0
mpls oam
interface tunnel-te 1 
 bfd 
  minimum-interval 500
  fast-detect
  multiplier 5
  bringup-timeout 60						
  lsp-ping disable                              
  dampening initial-wait    (default 16000 ms)
  dampening maximum-wait    (default 600000 ms)
  dampening secondary-wait  (default 20000 ms)
 logging events bfd-status

BFD Over MPLS TE Tunnel Tail-End Configuration: Example

This example shows how to configure BFD over MPLS TE Tunnels at tail-end.

Router# bfd multipath include loc 0/1/CPU0
mpls oam
mpls traffic-eng bfd lsp tail multiplier 3		
mpls traffic-eng bfd lsp tail minimum-interval 500

RFCs

RFCs

Title

rfc5880_bfd_base

Bidirectional Forwarding Detection, June 2010

rfc5881_bfd_ipv4_ipv6

BFD for IPv4 and IPv6 (Single Hop), June 2010

Technical Assistance

Description

Link

The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport