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Bidirectional Forwarding Detection

Table Of Contents

Bidirectional Forwarding Detection

Finding Feature Information

Contents

Prerequisites for Bidirectional Forwarding Detection

Restrictions for Bidirectional Forwarding Detection

Information About Bidirectional Forwarding Detection

BFD Operation

BFD Detection of Failures

BFD Version Interoperability

BFD Session

BFD Support for Non-Broadcast Media Interfaces

BFD Support for VPN Routing and Forwarding Interfaces

BFD Support for Nonstop Forwarding with Stateful Switchover

BFD Support for Static Routing

Benefits of Using BFD for Failure Detection

How to Configure Bidirectional Forwarding Detection

Configuring BFD Session Parameters on the Interface

Configuring BFD Support for Dynamic Routing Protocols

Configuring BFD Support for BGP

Configuring BFD Support for EIGRP

Configuring BFD Support for IS-IS

Configuring BFD Support for OSPF

Configuring BFD Support for Static Routing

Configuring BFD Echo Mode

Configuring the BFD Slow Timer

Disabling BFD Echo Mode Without Asymmetry

Configuration Examples for Bidirectional Forwarding Detection

Example: Configuring BFD Support for Static Routing

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Bidirectional Forwarding Detection


Bidirectional Forwarding Detection


First Published: January 14, 2008
Last Updated: July 15, 2010

This document describes how to enable the Bidirectional Forwarding Detection (BFD) protocol. BFD is a detection protocol that is designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Bidirectional Forwarding Detection" section.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

Prerequisites for Bidirectional Forwarding Detection

Restrictions for Bidirectional Forwarding Detection

Information About Bidirectional Forwarding Detection

How to Configure Bidirectional Forwarding Detection

Configuration Examples for Bidirectional Forwarding Detection

Additional References

Feature Information for Bidirectional Forwarding Detection

Prerequisites for Bidirectional Forwarding Detection

Cisco Express Forwarding and IP routing must be enabled on all participating routers.

One of the IP routing protocols supported by BFD must be configured on the routers before BFD is deployed. You should implement fast convergence for the routing protocol that you are using. See the IP routing documentation for your version of Cisco IOS XE software for information on configuring fast convergence. See the "Restrictions for Bidirectional Forwarding Detection" section for more information on BFD routing protocol support in Cisco IOS XE software.

Restrictions for Bidirectional Forwarding Detection

The Cisco implementation of BFD supports the following routing protocols: BGP, EIGRP, IS-IS, and OSPF.

BFD works only for directly connected neighbors. BFD neighbors must be no more than one IP hop away. Multihop configurations are not supported.

Information About Bidirectional Forwarding Detection

BFD Operation

Benefits of Using BFD for Failure Detection

BFD Operation

BFD provides a low-overhead, short-duration method of detecting failures in the forwarding path between two adjacent routers, including the interfaces, data links, and forwarding planes. BFD is a detection protocol that you enable at the interface and routing protocol levels. Cisco supports the BFD asynchronous mode, which depends on the sending of BFD control packets between two systems to activate and maintain BFD neighbor sessions between routers. Therefore, in order for a BFD session to be created, you must configure BFD on both systems (or BFD peers). Once BFD has been enabled on the interfaces and at the router level for the appropriate routing protocols, a BFD session is created, BFD timers are negotiated, and the BFD peers will begin to send BFD control packets to each other at the negotiated interval.

BFD provides fast BFD peer failure detection times independently of all media types, encapsulations, topologies, and routing protocols BGP, EIGRP, IS-IS, and OSPF. By sending rapid failure detection notices to the routing protocols in the local router to initiate the routing table recalculation process, BFD contributes to greatly reduced overall network convergence time. Figure 1 shows a simple network with two routers running OSPF and BFD. When OSPF discovers a neighbor (1) it sends a request to the local BFD process to initiate a BFD neighbor session with the OSPF neighbor router (2). The BFD neighbor session with the OSPF neighbor router is established (3).

Figure 1 Establishing a BFD Neighbor Relationship

Figure 2 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 will immediately start converging on it.

Figure 2 Tearing Down an OSPF Neighbor Relationship

BFD Detection of Failures

Once a BFD session has been established and timer negations are complete, BFD peers send BFD control packets that act in the same manner as an IGP hello protocol to detect liveliness, except at a more accelerated rate. The following information should be noted:

BFD is a forwarding path failure detection protocol. BFD detects a failure, but the routing protocol must take action to bypass a failed peer.

Typically, BFD can be used at any protocol layer. For Cisco IOS XE Release 2.1, BFD is supported for static routing.

BFD Version Interoperability

All BFD sessions appear as Version 1 by default and are interoperable with Version 0. The system automatically performs BFD version detection, and BFD sessions between neighbors will run in the highest common BFD version between neighbors. For example, of one BFD neighbor is running BFD Version 0 and the other BFD neighbor is running Version 1, the session will run BFD Version 0. The output from the show bfd neighbors [details] command will verify which BFD version a BFD neighbor is running.

BFD Session

The maximum number of BFD sessions that can be created is 500. The maximum number of BFD sessions for a stateful switchover is 128.

BFD Support for Non-Broadcast Media Interfaces

The BFD feature is supported on non-broadcast media interfaces including ATM, POS, serial, and VLAN interfaces. BFD support extends to ATM, FR, POS, and serial subinterfaces as well.

The bfd interval command must be configured on the interface to initiate BFD monitoring.

BFD Support for VPN Routing and Forwarding Interfaces

The BFD feature is VPN Routing and Forwarding (VRF) aware to provide fast detection of routing protocol failures between provider edge (PE) and customer edge (CE) routers.

BFD Support for Nonstop Forwarding with Stateful Switchover

Cisco IOS XE software supports BFD stateful switchover (SSO) for both planned and unplanned switchovers. Typically, when a networking device restarts, all routing peers of that device detect that the device went down and then came back up. This transition results in a routing flap, which could spread across multiple routing domains. Routing flaps caused by router restarts create routing instabilities, which are detrimental to the overall network performance. Nonstop forwarding (NSF) helps to suppress routing flaps in devices that are enabled with SSO, thereby reducing network instability.

NSF allows for the forwarding of data packets to continue along known routes while the routing protocol information is being restored after a switchover. With NSF, peer networking devices do not experience routing flaps. Data traffic is forwarded through intelligent line cards or dual forwarding processors while the standby RP assumes control from the failed active RP during a switchover. The ability of line cards and forwarding processors to remain up through a switchover and to be kept current with the Forwarding Information Base (FIB) on the active RP is key to NSF operation.

In devices that support dual RPs, SSO establishes one of the RPs as the active processor while the other RP is designated as the standby processor, and then synchronizes information between them. A switchover from the active to the standby processor occurs when the active RP fails, when it is removed from the networking device, or when it is manually taken down for maintenance.

BFD Support for Static Routing

Unlike dynamic routing protocols, such as OSPF and BGP, static routing has no method of peer discovery. Therefore, when BFD is configured, the reachability of the gateway is completely dependent on the state of the BFD session to the specified neighbor. Unless the BFD session is up, the gateway for the static route is considered unreachable, and therefore the affected routes will not be installed in the appropriate RIB.

For a BFD session to be successfully established, BFD must be configured on the interface on the peer and there must be a BFD client registered on the peer for the address of the BFD neighbor. When an interface is used by dynamic routing protocols, the latter requirement is usually met by configuring the routing protocol instances on each neighbor for BFD. When an interface is used exclusively for static routing, this requirement must be met by configuring static routes on the peers.

If a BFD configuration is removed from the remote peer while the BFD session is in the up state, the updated state of the BFD session is not signaled to IPv4 static. This will cause the static route to remain in the RIB. The only workaround is to remove the IPv4 static BFD neighbor configuration so that the static route no longer tracks BFD session state. Also, if you change the encapsulation type on a serial interface to one that is unsupported by BFD, BFD will be in a down state on that interface. The workaround is to shut down the interface, change to a supported encapsulation type, and then reconfigure BFD.

Benefits of Using BFD for Failure Detection

When you deploy any feature, it is important to consider all the alternatives and be aware of any trade-offs being made.

The closest alternative to BFD in conventional EIGRP, IS-IS, and OSPF deployments is the use of modified failure detection mechanisms for EIGRP, IS-IS, and OSPF routing protocols.

If you set EIGRP hello and hold timers to their absolute minimums, the failure detection rate for EIGRP falls to within a one- to two-second range.

If you use fast hellos for either IS-IS or OSPF, these Interior Gateway Protocol (IGP) protocols reduce their failure detection mechanisms to a minimum of one second.

There are several advantages to implementing BFD over reduced timer mechanisms for routing protocols:

Although reducing the EIGRP, IS-IS, and OSPF timers can result in minimum detection timer of one to two seconds, BFD can provide failure detection in less than one second.

Because BFD is not tied to any particular routing protocol, it can be used as a generic and consistent failure detection mechanism for EIGRP, IS-IS, and OSPF.

Because some parts of BFD can be distributed to the data plane, it can be less CPU-intensive than the reduced EIGRP, IS-IS, and OSPF timers, which exist wholly at the control plane.

How to Configure Bidirectional Forwarding Detection

You start a BFD process by configuring BFD on the interface. When the BFD process is started, no entries are created in the adjacency database; in other words, no BFD control packets are sent or received. BFD echo mode is enabled by default. BFD echo packets are sent and received in addition to BFD control packets. The adjacency creation takes places once you have configured BFD support for the applicable routing protocols. This section contains the following procedures:

Configuring BFD Session Parameters on the Interface (required)

Configuring BFD Support for Dynamic Routing Protocols (required)

Configuring BFD Support for Static Routing (optional)

Configuring BFD Echo Mode (optional)

Configuring BFD Session Parameters on the Interface

The steps in this procedure show how to configure BFD on the interface by setting the baseline BFD session parameters on an interface. Repeat the steps in this procedure for each interface over which you want to run BFD sessions to BFD neighbors.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

5. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number

Example:

Router(config)# interface GigabitEthernet 6/0/0

Enters interface configuration mode.

Step 4 

bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

Example:

Router(config-if)# bfd interval 50 min_rx 50 multiplier 5

Enables BFD on the interface.

Step 5 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Configuring BFD Support for Dynamic Routing Protocols

You can enable BFD support for dynamic routing protocols at the router level to enable BFD support globally for all interfaces or you can configure BFD on a per-interface basis at the interface level.

For Cisco IOS XE Release 2.1, the Cisco implementation of BFD supports the following routing protocols: BGP, EIGRP, IS-IS, and OSPF.

This section describes the following procedures:

Configuring BFD Support for BGP (optional)

Configuring BFD Support for EIGRP (optional)

Configuring BFD Support for IS-IS (optional)

Configuring BFD Support for OSPF (optional)

Configuring BFD Support for BGP

This section describes the procedure for configuring BFD support for BGP, so that BGP is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD.

Prerequisites

BGP must be running on all participating routers.

You must configure the baseline parameters for BFD sessions on the interfaces over which you want to run BFD sessions. See the "Configuring BFD Session Parameters on the Interface" section for more information.

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp as-tag

4. neighbor ip-address fall-over bfd

5. end

6. show bfd neighbors [details]

7. show ip bgp neighbor

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router bgp as-tag
Example:

Router(config)# router bgp tag1

Specifies a BGP process and enters router configuration mode.

Step 4 

neighbor ip-address fall-over bfd

Example:

Router(config-router)# neighbor 172.16.10.2 fall-over bfd

Enables BFD support for fallover.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode and returns to privileged EXEC mode.

Step 6 

show bfd neighbors [details]

Example:

Router# show bfd neighbors detail

(Optional) Verifies that the BFD neighbor is active and displays the routing protocols that BFD has registered.

Step 7 

show ip bgp neighbor

Example:

Router# show ip bgp neighbor

(Optional) Displays information about BGP and TCP connections to neighbors.

What to Do Next

If you want to configure BFD support for another routing protocol, see the following sections:

Configuring BFD Support for EIGRP

Configuring BFD Support for IS-IS

Configuring BFD Support for OSPF

Configuring BFD Support for EIGRP

This section describes the procedure for configuring BFD support for EIGRP, so that EIGRP is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD. There are two methods for enabling BFD support for EIGRP:

You can enable BFD for all of the interfaces for which EIGRP is routing by using the bfd all-interfaces command in router configuration mode.

You can enable BFD for a subset of the interfaces for which EIGRP is routing by using the bfd interface command in router configuration mode.

Prerequisites

EIGRP must be running on all participating routers.

The baseline parameters for BFD sessions on the interfaces over which you want to run BFD sessions to BFD neighbors must be configured. See the "Configuring BFD Session Parameters on the Interface" section for more information.

SUMMARY STEPS

1. enable

2. configure terminal

3. router eigrp as-number

4. bfd all-interfaces
or
bfd interface type number

5. end

6. show bfd neighbors [details]

7. show ip eigrp interfaces [type number] [as-number] [detail]

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router eigrp as-number

Example:

Router(config)# router eigrp 123

Configures the EIGRP routing process and enters router configuration mode.

Step 4 

bfd all-interfaces

or

bfd interface type number

Example:

Router(config-router)# bfd all-interfaces

or

Example:

Router(config-router)# bfd interface GigabitEthernet 6/0/0

Enables BFD globally on all interfaces associated with the EIGRP routing process.

or

Enables BFD on a per-interface basis for one or more interfaces associated with the EIGRP routing process.

Step 5 

end

Example:

Router(config-router) end

Exits router configuration mode and returns to privileged EXEC mode.

Step 6 

show bfd neighbors [details]

Example:

Router# show bfd neighbors details

(Optional) Verifies that the BFD neighbor is active and displays the routing protocols that BFD has registered.

Step 7 

show ip eigrp interfaces [type number] [as-number] [detail]

Example:

Router# show ip eigrp interfaces detail

(Optional) Displays the interfaces for which BFD support for EIGRP has been enabled.

What to Do Next

If you want to configure BFD support for another routing protocol, see the following sections:

Configuring BFD Support for BGP

Configuring BFD Support for IS-IS

Configuring BFD Support for OSPF

Configuring BFD Support for IS-IS

This section describes the procedures for configuring BFD support for IS-IS, so that IS-IS is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD. There are two methods for enabling BFD support for IS-IS:

You can enable BFD for all of the interfaces on which IS-IS is supporting IPv4 routing by using the bfd all-interfaces command in router configuration mode. You can then disable BFD for one or more of those interfaces using the isis bfd disable command in interface configuration mode.

You can enable BFD for a subset of the interfaces for which IS-IS is routing by using the isis bfd command in interface configuration mode.

To configure BFD support for IS-IS, perform the steps in one of the following sections:

Configuring BFD Support for IS-IS for All Interfaces

Configuring BFD Support for IS-IS for One or More Interfaces

Prerequisites

IS-IS must be running on all participating routers.

The baseline parameters for BFD sessions on the interfaces that you want to run BFD sessions to BFD neighbors over must be configured. See the "Configuring BFD Session Parameters on the Interface" section for more information.

Configuring BFD Support for IS-IS for All Interfaces

To configure BFD on all IS-IS interfaces that support IPv4 routing, perform the steps in this section.

SUMMARY STEPS

1. enable

2. configure terminal

3. router isis [area-tag]

4. bfd all-interfaces

5. exit

6. interface type number

7. ip router isis [tag]

8. isis bfd [disable]

9. end

10. show bfd neighbors [details]

11. show clns interface

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router isis area-tag
Example:

Router(config)# router isis tag1

Specifies an IS-IS process and enters router configuration mode.

Step 4 

bfd all-interfaces

Example:

Router(config-router)# bfd all-interfaces

Enables BFD globally on all interfaces associated with the IS-IS routing process.

Step 5 

exit

Example:

Router(config-router)# exit

(Optional) Returns to global configuration mode.

Step 6 

interface type number
Example:

Router(config)# interface gigabitethernet 6/0/0

(Optional) Enters interface configuration mode.

Step 7 

ip router isis [tag]
Example:

Router(config-if)# ip router isis tag1

(Optional) Enables support for IPv4 routing on the interface.

Step 8 

isis bfd [disable]

Example:

Router(config-if)# isis bfd

(Optional) Enables or disables BFD on a per-interface basis for one or more interfaces associated with the IS-IS routing process.

Note You should use the disable keyword only if you enabled BFD on all of the interfaces that IS-IS is associated with using the bfd all-interfaces command in router configuration mode.

Step 9 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 10 

show bfd neighbors [details]

Example:

Router# show bfd neighbors details

(Optional) Displays information that can be used to verify if the BFD neighbor is active and displays the routing protocols that BFD has registered.

Step 11 

show clns interface

Example:

Router# show clns interface

(Optional) Displays information that can be used to verify if BFD for IS-IS has been enabled for a specific IS-IS interface that is associated.

What to Do Next

If you want to configure only for a specific subset of interfaces, perform the tasks in the "Configuring BFD Support for IS-IS for One or More Interfaces" section.

Configuring BFD Support for IS-IS for One or More Interfaces

To configure BFD for only one or more IS-IS interfaces, perform the steps in this section.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip router isis [tag]

5. isis bfd [disable]

6. end

7. show bfd neighbors [details]

8. show clns interface

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number
Example:

Router(config)# interface gigabitethernet 6/0/0

Enters interface configuration mode.

Step 4 

ip router isis [tag]
Example:

Router(config-if)# ip router isis tag1

Enables support for IPv4 routing on the interface.

Step 5 

isis bfd [disable]

Example:

Router(config-if)# isis bfd

Enables or disables BFD on a per-interface basis for one or more interfaces associated with the IS-IS routing process.

Note You should use the disable keyword only if you enabled BFD on all of the interfaces that IS-IS is associated with using the bfd all-interfaces command in router configuration mode.

Step 6 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 7 

show bfd neighbors [details]

Example:

Router# show bfd neighbors details

(Optional) Displays information that can help verify if the BFD neighbor is active and displays the routing protocols that BFD has registered.

Step 8 

show clns interface

Example:

Router# show clns interface

(Optional) Displays information that can help verify if BFD for IS-IS has been enabled for a specific IS-IS interface that is associated.

What to Do Next

If you want to configure BFD support for another routing protocol, see one of the following sections:

Configuring BFD Support for BGP

Configuring BFD Support for EIGRP

Configuring BFD Support for OSPF

Configuring BFD Support for OSPF

This section describes the procedures for configuring BFD support for OSPF, so that OSPF is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD. You can either configure BFD support for OSPF globally on all interfaces or configure it selectively on one or more interfaces.

There are two methods for enabling BFD support for OSPF:

You can enable BFD for all of the interfaces for which OSPF is routing by using the bfd all-interfaces command in router configuration mode. You can disable BFD support on individual interfaces using the ip ospf bfd [disable] command in interface configuration mode.

You can enable BFD for a subset of the interfaces for which OSPF is routing by using the ip ospf bfd command in interface configuration mode.

See the following sections for tasks for configuring BFD support for OSPF:

Configuring BFD Support for OSPF for All Interfaces (optional)

Configuring BFD Support for OSPF for One or More Interfaces (optional)

Configuring BFD Support for OSPF for All Interfaces

To configure BFD for all OSPF interfaces, perform the steps in this section.

If you do not want to configure BFD on all OSPF interfaces and would rather configure BFD support specifically for one or more interfaces, see the "Configuring BFD Support for OSPF for One or More Interfaces" section.

Prerequisites

OSPF must be running on all participating routers.

The baseline parameters for BFD sessions on the interfaces over which you want to run BFD sessions to BFD neighbors must be configured. See the "Configuring BFD Session Parameters on the Interface" section for more information.

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. bfd all-interfaces

5. exit

6. interface type number

7. ip ospf bfd [disable]

8. end

9. show bfd neighbors [details]

10. show ip ospf

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router ospf process-id
Example:

Router(config)# router ospf 4

Specifies an OSPF process and enters router configuration mode.

Step 4 

bfd all-interfaces

Example:

Router(config-router)# bfd all-interfaces

Enables BFD globally on all interfaces associated with the OSPF routing process.

Step 5 

exit

Example:

Router(config-router)# exit

(Optional) Returns to global configuration mode. Enter this command only if you want to perform Step 7 to disable BFD for one or more interfaces.

Step 6 

interface type number

Example:

Router(config)# interface gigabitethernet 6/0/0

(Optional) Enters interface configuration mode. Enter this command only if you want to perform Step 7 to disable BFD for one or more interfaces.

Step 7 

ip ospf bfd [disable]

Example:

Router(config-if)# ip ospf bfd disable

(Optional) Disables BFD on a per-interface basis for one or more interfaces associated with the OSPF routing process.

Note You should use the disable keyword only if you enabled BFD on all of the interfaces that OSPF is associated with using the bfd all-interfaces command in router configuration mode.

Step 8 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 9 

show bfd neighbors [details]

Example:

Router# show bfd neighbors detail

(Optional) Displays information that can help verify if the BFD neighbor is active and displays the routing protocols that BFD has registered.

Step 10 

show ip ospf

Example:

Router# show ip ospf

(Optional) Displays information that can help verify if BFD for OSPF has been enabled.

What to Do Next

If you want to configure BFD support for another routing protocol, see the following sections:

Configuring BFD Support for BGP

Configuring BFD Support for EIGRP

Configuring BFD Support for IS-IS

Configuring BFD Support for OSPF for One or More Interfaces

To configure BFD on one or more OSPF interfaces, perform the steps in this section.

Prerequisites

OSPF must be running on all participating routers.

The baseline parameters for BFD sessions on the interfaces over which you want to run BFD sessions to BFD neighbors must be configured. See the "Configuring BFD Session Parameters on the Interface" section for more information.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip ospf bfd [disable]

5. end

6. show bfd neighbors [details]

7. show ip ospf

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number
Example:

Router(config)# interface gigabitethernet 6/0/0

Enters interface configuration mode.

Step 4 

ip ospf bfd [disable]

Example:

Router(config-if)# ip ospf bfd

Enables or disables BFD on a per-interface basis for one or more interfaces associated with the OSPF routing process.

Note You should use the disable keyword only if you enabled BFD on all of the interfaces that OSPF is associated with using the bfd all-interfaces command in router configuration mode.

Step 5 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 6 

show bfd neighbors [details]

Example:

Router# show bfd neighbors details

(Optional) Displays information that can help verify if the BFD neighbor is active and displays the routing protocols that BFD has registered.

Step 7 

show ip ospf

Example:

Router# show ip ospf

(Optional) Displays information that can help verify if BFD support for OSPF has been enabled.

What to Do Next

If you want to configure BFD support for another routing protocol, see the following sections:

Configuring BFD Support for BGP

Configuring BFD Support for EIGRP

Configuring BFD Support for IS-IS

Configuring BFD Support for Static Routing

Perform this task to configure BFD support for static routing.

Repeat the steps in this procedure on each BFD neighbor. For more information, see the "Example: Configuring BFD Support for Static Routing" section.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip address ip-address mask

5. bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

6. ip route static bfd interface-type interface-number gateway

7. ip route [vrf vrf-name] prefix mask {ip-address | interface-type interface-number [ip-address]} [dhcp] [distance] [name next-hop-name] [permanent | track number] [tag tag]

8. end

9. show ip static route

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number

Example:

Router(config)# interface serial 2/0/0

Configures an interface and enters interface configuration mode.

Step 4 

ip address ip-address mask

Example:

Router(config-if)# ip address 10.201.201.1 255.255.255.0

Configures an IP address for the interface.

Step 5 

bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

Example:

Router(config-if)# bfd interval 500 min_rx 500 multiplier 5

Enables BFD on the interface.

Step 6 

ip route static bfd interface-type interface-number gateway

Example:

Router(config-if)# ip route static bfd
Serial 2/0/0 10.201.201.2

Specifies a static route BFD neighbor.

The interface-type interface-number and gateway arguments are required because BFD support exists only for directly connected neighbors.

Step 7 

ip route [vrf vrf-name] prefix mask {ip-address | interface-type interface-number [ip-address]} [dhcp] [distance] [name next-hop-name] [permanent | track number] [tag tag]

Example:

Router(config-if)# ip route 10.0.0.0 255.0.0.0

Serial 2/0/0 10.201.201.2

Specifies a static route BFD neighbor.

Step 8 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 9 

show ip static route

Example:

Router# show ip static route

(Optional) Displays the static process local Routing Information Base (RIB) information.

Configuring BFD Echo Mode

This section contains the following configuration tasks for BFD echo mode:

Configuring the BFD Slow Timer

Disabling BFD Echo Mode Without Asymmetry

BFD echo mode is enabled by default, but you can disable it such that it can run independently in each direction. Before you configure echo mode, you should be familiar with the following concepts:

BFD Echo Mode

Prerequisites

BFD Echo Mode

Benefits of Running BFD Echo Mode

BFD echo mode works with asynchronous BFD. Echo packets are sent by the forwarding engine and forwarded back along the same path in order to perform detection—the BFD session at the other end does not participate in the actual forwarding of the echo packets. The echo function and the forwarding engine are responsible for the detection process, therefore the number of BFD control packets that are sent out between two BFD neighbors is reduced. And since the forwarding engine is testing the forwarding path on the remote (neighbor) system without involving the remote system, there is an opportunity to improve the interpacket delay variance, thereby achieving quicker failure detection times than when using BFD Version 0 with BFD control packets for the BFD session.

Echo Mode Without Asymmetry

Echo mode is described as without asymmetry when it is running on both sides (both BFD neighbors are running echo mode).

Prerequisites

BFD must be running on all participating routers.

Before using BFD echo mode, you must disable the sending of Internet Control Message Protocol (ICMP) redirect messages by entering the no ip redirects command, in order to avoid high CPU utilization.

The baseline parameters for BFD sessions on the interfaces over which you want to run BFD sessions to BFD neighbors must be configured. See the "Configuring BFD Session Parameters on the Interface" section for more information.

Configuring the BFD Slow Timer

The steps in this procedure show how to change the value of the BFD slow timer. Repeat the steps in this procedure for each BFD router.

SUMMARY STEPS

1. enable

2. configure terminal

3. bfd slow-timer milliseconds

4. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

bfd slow-timer milliseconds

Example:

Router(config)# bfd slow-timer 12000

Configures the BFD slow timer.

Step 4 

end

Example:

Router(config)# end

Exits global configuration mode and returns to privileged EXEC mode.

Disabling BFD Echo Mode Without Asymmetry

The steps in this procedure show how to disable BFD echo mode without asymmetry—no echo packets will be sent by the router, and the router will not forward BFD echo packets that are received from any neighbor routers.

Repeat the steps in this procedure for each BFD router.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. no bfd echo

5. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number

Example:

Router(config)# interface GigabitEthernet 6/0/0

Enters interface configuration mode.

Step 4 

no bfd echo

Example:

Router(config-if)# no bfd echo

Disables BFD echo mode.

Step 5 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to global configuration mode.

Configuration Examples for Bidirectional Forwarding Detection

This section provides the following configuration example:

Example: Configuring BFD Support for Static Routing

Example: Configuring BFD Support for Static Routing

In the following example, the network consists of Router A and Router B. Serial interface 2/0/0 on Router A is connected to the same network as serial interface 2/0 on Router B. In order for the BFD session to come up, Router B must be configured.

Router A

configure terminal
  ip route static bfd Serial 2/0/0 10.201.201.2
  ip route 10.0.0.0 255.0.0.0 Serial 2/0/0 10.201.201.2
  interface Serial 2/0/0
  ip address 10.201.201.1 255.255.255.0
  bfd interval 500 min_rx 500 multiplier 5

 Router B

configure terminal
  ip route static bfd Serial 2/0/0 10.201.201.1
  ip route 10.1.1.1 255.255.255.255 Serial 2/0/0 10.201.201.1
  interface Serial 2/0/0
  ip address 10.201.201.2 255.255.255.0
  bfd interval 500 min_rx 500 multiplier 5

Note that the static route on Router B exists solely to enable the BFD session between 10.201.201.1 and 10.201.201.2. If there is no useful static route that needs to be configured, select a prefix that will not affect packet forwarding; for example, the address of a locally configured loopback interface.

Additional References

Related Documents

Related Topic
Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

Static route support for BFD in IPv6

OSPF for IPv6 in BFD

"Implementing Bidirectional Forwarding Detection for IPv6" module of the Cisco IOS XE IPv6 Configuration Guide, Release 2

Configuring and monitoring BGP

"Cisco BGP Overview" module of the Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2

Configuring and monitoring EIGRP

"Configuring EIGRP" module of the Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2

Configuring and monitoring IS-IS

"Integrated IS-IS Routing Protocol Overview" module of the Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2

Configuring and monitoring OSPF

"Configuring OSPF" module of the Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2

BFD commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

Cisco IOS IP Routing: Protocol-Independent Command Reference

BGP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

Cisco IOS IP Routing: BGP Command Reference

EIGRP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

Cisco IOS IP Routing: EIGRP Command Reference

IS-IS commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

Cisco IOS IP Routing: ISIS Command Reference

OSPF commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

Cisco IOS IP Routing: OSPF Command Reference


Standards

Standard
Title

IETF Draft

Bidirectional Forwarding Detection, January 2006

(http://www.ietf.org/internet-drafts/draft-ietf-bfd-base-03.txt)

IETF Draft

BFD for IPv4 and IPv6 (Single Hop), March 2005

(http://www.ietf.org/internet-drafts/draft-ietf-bfd-v4v6-1hop-02.txt)


MIBs

MIB
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html


Feature Information for Bidirectional Forwarding Detection

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.


Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.


Table 1 Feature Information for Bidirectional Forwarding Detection 

Feature Name
Releases
Feature Information

Bidirectional Forwarding Detection (standard implementation, Version 1)

Cisco IOS XE
Release 2.1

This document describes how to enable the BFD protocol. BFD is a detection protocol that is designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable.

This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

BFD Echo Mode

Cisco IOS XE
Release 2.1

BFD echo mode works with asynchronous BFD. Echo packets are sent by the forwarding engine and forwarded back along the same path in order to perform detection—the BFD session at the other end does not participate in the actual forwarding of the echo packets. The echo function and the forwarding engine are responsible for the detection process, therefore the number of BFD control packets that are sent out between two BFD neighbors is reduced. And since the forwarding engine is testing the forwarding path on the remote (neighbor) system without involving the remote system, there is an opportunity to improve the interpacket delay variance, thereby achieving quicker failure detection times than when using BFD Version 0 with BFD control packets for the BFD session.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

Configuring BFD Echo Mode

Disabling BFD Echo Mode Without Asymmetry

BFD—EIGRP Support

Cisco IOS XE
Release 2.1

BFD support for EIGRP can be configured so that EIGRP is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following section provides information about this feature:

Configuring BFD Support for Dynamic Routing Protocols

Configuring BFD Support for EIGRP

BFD—VRF Support

Cisco IOS XE
Release 2.1

The BFD feature support is extended to be VRF aware to provide fast detection of routing protocol failures between PE and CE routers.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

BFD Support for VPN Routing and Forwarding Interfaces

BFD—WAN Interface Support

Cisco IOS XE
Release 2.1

BFD feature is supported on non-broadcast media interfaces including ATM, POS, serial, and VLAN interfaces. BFD support extends to ATM, FR, POS, and serial subinterfaces as well.

The bfd interval command must be configured on the interface to initiate BFD monitoring.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

BFD Support for Non-Broadcast Media Interfaces

IS-IS Support for BFD over IPv4

Cisco IOS XE
Release 2.1

BFD support for OSPF can be configured globally on all interfaces or configured selectively on one or more interfaces. When BFD support is configured with IS-IS as a registered protocol with BFD, IS-IS receives forwarding path detection failure messages from BFD.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

Configuring BFD Support for Dynamic Routing Protocols

Configuring BFD Support for IS-IS

OSPF Support for BFD over IPv4

Cisco IOS XE
Release 2.1

BFD support for OSPF can be configured globally on all interfaces or configured selectively on one or more interfaces. When BFD support is configured with OSPF as a registered protocol with BFD, OSPF receives forwarding path detection failure messages from BFD.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

Configuring BFD Support for Dynamic Routing Protocols

Configuring BFD Support for OSPF

SSO—BFD

Cisco IOS XE
Release 2.1

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

BFD Support for Nonstop Forwarding with Stateful Switchover

Static Routes for BFD

Cisco IOS XE
Release 2.1

Unlike dynamic routing protocols, such as OSPF and BGP, static routing has no method of peer discovery. Therefore, when BFD is configured, the reachability of the gateway is completely dependent on the state of the BFD session to the specified neighbor. Unless the BFD session is up, the gateway for the static route is considered unreachable, and therefore the affected routes will not be installed in the appropriate RIB.

This feature was introduced on the Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

BFD Support for Static Routing

Configuring BFD Support for Static Routing

Example: Configuring BFD Support for Static Routing