- Preface
- New and Changed Information
- Overview
- Configuring IPv4
- Configuring OSPFv2
- Configuring EIGRP
- Configuring Basic BGP
- Configuring Advanced BGP
- Configuring BGP Additional Paths
- Configuring RIP
- Configuring Static Routing
- Configuring Layer 3 Virtualization
- Configuring the Unicast RIB and FIB
- Configuring Route Policy Manager
- Configuring Bidirectional Forwarding Detection
- Configuring Policy-Based Routing
- Configuring HSRP
- Configuring VRRP
- Configuring Object Tracking
- IETF RFCs
Cisco Nexus 3548 Switch NX-OS Unicast Routing Configuration Guide, Release 6.x
- Updated:
- March 20, 2018
Chapter: Configuring Bidirectional Forwarding Detection
- Information About BFD
- Licensing Requirements for BFD
- Prerequisites for BFD
- Guidelines and Limitations
- Default Settings
- Configuring BFD
- Configuration Hierarchy
- Task Flow for Configuring BFD
- Enabling the BFD Feature
- Configuring Global BFD Parameters
- Configuring BFD on an Interface
- Configuring BFD on a Port Channel
- Configuring the BFD Echo Function
- Optimizing BFD on Subinterfaces
- Configuring BFD on BGP
- Configuring BFD on PIM
- Configuring BFD on OSPFv2
- Configuring BFD for Static Routes
- Verifying the BFD Configuration
- Monitoring BFD
Configuring Bidirectional Forwarding Detection
This chapter describes how to configure Bidirectional Forwarding Detection (BFD).
This chapter includes the following sections:
- Information About BFD
- Licensing Requirements for BFD
- Prerequisites for BFD
- Guidelines and Limitations
- Default Settings
- Configuring BFD
- Verifying the BFD Configuration
- Monitoring BFD
Information About BFD
BFD is a detection protocol designed to provide fast forwarding-path failure detection times for media types, encapsulations, topologies, and routing protocols. You can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different protocol hello mechanisms. BFD makes network profiling and planning easier and reconvergence time consistent and predictable.
BFD provides subsecond failure detection between two adjacent devices.
Asynchronous Mode
Cisco NX-OS supports the BFD asynchronous mode, which sends BFD control packets between two adjacent devices to activate and maintain BFD neighbor sessions between the devices. You configure BFD on both devices (or BFD neighbors). Once BFD has been enabled on the appropriate protocols, Cisco NX-OS creates a BFD session, negotiates BFD session parameters, and begins to send BFD control packets to each BFD neighbor at the negotiated interval. The BFD session parameters include the following:
-
Desired minimum transmit interval—The interval at which this device wants to send BFD hello messages.
-
Required minimum receive interval—The minimum interval at which this device can accept BFD hello messages from another BFD device.
-
Detect multiplier—The number of missing BFD hello messages from another BFD device before this local device detects a fault in the forwarding path.
BFD Detection of Failures
Once a BFD session has been established and timer negotiations are complete, BFD neighbors send BFD control packets that act in the same manner as an IGP hello protocol to detect liveliness, except at a more accelerated rate. BFD detects a failure, but the protocol must take action to bypass a failed peer.
BFD sends a failure detection notice to the BFD-enabled protocols when it detects a failure in the forwarding path. The local device can then initiate the protocol recalculation process and reduce the overall network convergence time.
When a failure occurs in the network, the following occurs:
-
1. The BFD neighbor session with the BFD neighbor router is torn down.
-
2. BFD notifies the local BFD process that the BFD neighbor is no longer reachable.
-
3. The local BFD process tears down the BFD neighbor relationship.
-
4. If an alternative path is available, the routers immediately start converging on it.
 Note | The BFD failure detection occurs in less than a second. |
BFD Echo Function
The BFD echo function sends echo packets from the forwarding engine to the remote BFD neighbor. The BFD neighbor forwards the echo packet back along the same path in order to perform detection; the BFD neighbor does not participate in the actual forwarding of the echo packets. The echo function and the forwarding engine are responsible for the detection process. BFD can use the slow timer to slow down the asynchronous session when the echo function is enabled and reduce the number of BFD control packets that are sent between two BFD neighbors. Also, the forwarding engine tests the forwarding path on the remote (neighbor) system without involving the remote system, so there is less interpacket delay variability and faster failure detection times.
The echo function is asymmetrical when both BFD neighbors are running echo function.
Security
Cisco NX-OS uses the packet Time to Live (TTL) value to verify that the BFD packets came from an adjacent BFD peer. For all asynchronous and echo request packets, the BFD neighbor sets the TTL value to 255 and the local BFD process verifies the TTL value as 255 before processing the incoming packet. For the echo response packet, BFD sets the TTL value to 254.
Virtualization Support
BFD supports virtual routing and forwarding instances (VRFs).
Licensing Requirements for BFD
The following table shows the licensing requirements for this feature:
|
Product |
License Requirement |
|---|---|
|
Cisco NX-OS |
BFD requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide. |
Prerequisites for BFD
BFD has the following prerequisites:
-
You must enable the BFD feature (see the Enabling the BFD Feature section).
-
For any client protocols that you want to enable BFD on, you enable BFD in that client protocol.
-
Disable Internet Control Message Protocol (ICMP) redirect messages on a BFD-enabled interfaces.
-
See other detailed prerequisites that are listed with the configuration tasks.
-
Beginning with Cisco NX-OS Release 6.0(2)A4(1), BFD for BGP and PIM are supported.
Guidelines and Limitations
BFD has the following configuration guidelines and limitations:
-
BFD supports BFD version 1.
-
BFD supports IPv4, BGPv4, PIM and static routes.
-
BFD supports single-hop BFD.
-
BFD for BGP supports single-hop eBGP and iBGP with an update source.
-
BFD supports the following Layer 3 interfaces—physical interfaces, port channels, subinterfaces, and VLAN interfaces (SVI).
-
BFD does not support authentication for BFD or per-link BFD sessions on a port channel.
-
BFD depends on a Layer 3 adjacency information to discover topology changes, including Layer 2 topology changes. A BFD session on a VLAN interface (SVI) may not be up after the convergence of the Layer 2 topology if there is no Layer 3 adjacency information available.
-
Port channel configuration limitations:
– For Layer 3 port channels used by BFD, you must enable the Link Aggregation Control Protocol (LACP) on the port channel.
– For Layer 2 port channels used by SVI sessions, you must enable LACP on the port channel.
-
SVI limitations:
– When you change the topology (for example, add or delete a link into a VLAN, delete a member from a Layer 2 port channel, and so on), the SVI session could be affected. It may go down first and then come up after the topology discovery is finished.
 Tip | If you do not want the SVI sessions to flap and you need to change the topology, you can disable the BFD feature before making the changes and reenable BFD after the changes have been made. You can also configure the BFD timer to be a large value (for example, 5 seconds), and change it back to a fast timer after the above events complete. |
-
Cisco NX-OS does not distribute the BFD operation to compatible modules to offload the CPU for BFD packet processing.
-
BFD does not support stateless restarts and in-service software upgrades (ISSUs).
-
If you want to enable BFD for a peer reachable through a port channel, you must configure LACP on the port channel.
-
Cisco Nexus 3548 cannot be an intermediate switch to forward BFD echo packets.
Default Settings
Table below lists the default settings for BFD parameters.
|
Parameters |
Default |
|---|---|
|
BFD feature |
Disabled |
|
Required minimum receive interval |
250 milliseconds |
|
Desired minimum transmit interval |
250 milliseconds |
|
Detect multiplier |
3 |
|
Echo function |
Enabled |
|
Mode |
Asynchronous |
|
Port channel |
Logical mode (one session per source-destination pair address) |
|
Slow timer |
2000 milliseconds |
|
Subinterface optimization |
Disabled |
Configuring BFD
This section includes the following topics:
- Configuration Hierarchy
- Task Flow for Configuring BFD
- Enabling the BFD Feature
- Configuring Global BFD Parameters
- Configuring BFD on an Interface
- Configuring BFD on a Port Channel
- Configuring the BFD Echo Function
- Optimizing BFD on Subinterfaces
- Configuring BFD on BGP
- Configuring BFD on PIM
- Configuring BFD on OSPFv2
- Configuring BFD for Static Routes
Configuration Hierarchy
You can configure BFD at the global level, VRF level, at the interface or port channel level, or at the subinterface level (for physical interfaces and port channels). The VRF configuration overrides global configuration. The interface or port channel configuration overrides VRF or global configuration. On supported interfaces, the subinterface-level configuration overrides the interface or port channel configuration unless subinterface optimization is enabled. See the Optimizing BFD on Subinterfaces section for more information.
For physical ports that are members of a port channel, the member port inherits the master port channel BFD configuration. The member port subinterfaces can override the master port channel BFD configuration, unless subinterface optimization is enabled.
Task Flow for Configuring BFD
Follow these steps to configure BFD:
| Step 1 | Enabling the BFD Feature. |
| Step 2 | Configuring Global BFD Parameters or Configuring BFD on an Interface. |
| Step 3 | Configuring BFD on BGP. |
Enabling the BFD Feature
You must enable the BFD feature before you can configure BFD on an interface and protocol.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | feature bfd Example: switch(config)# feature bfd |
Enables the BFD feature. |
| Step 3 | copy running-config startup-config Example: switch(config)# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring Global BFD Parameters
You can configure the BFD session parameters for all BFD sessions on the device. The BFD session parameters are negotiated between the BFD peers in a three-way handshake.
See the Configuring BFD on an Interface section to override these global session parameters on an interface.
Enable the BFD feature. See the Enabling the BFD Feature section.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | bfd interval
mintx
min_rx
msec multiplier
value Example: switch(config)# bfd interval 250 min_rx 250 multiplier 3 |
Configures the BFD session parameters for all BFD sessions on the device. You can override these values by configuring the BFD session parameters on an interface. The mintx and msec range is from 250 to 999 milliseconds and the default is 250. The multiplier range is from 3 to 50. The multiplier default is 3. To return to the default settings, use the no bfd interval command. |
| Step 3 | bfd slow-timer [ interval ] Example: switch(config)# bfd slow-timer 2000 |
Configures the slow timer. This value determines how fast BFD starts up a new session and is used to slow down the asynchrounous sessions when the BFD echo function is enabled. The range is from 1000 to 30000 milliseconds. The default is 2000. To return to the default settings, use the no bfd slow-timer command. |
| Step 4 | exit Example: switch(config)# exit switch# |
Returns to EXEC mode. |
| Step 5 | show running-config bfd Example: switch# show running-config bfd | (Optional)
Displays the BFD running configuration. |
| Step 6 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring BFD on an Interface
Enable the BFD feature. See the Enabling the BFD Feature section.
You can configure the BFD session parameters for all BFD sessions on an interface. The BFD session parameters are negotiated between the BFD peers in a three-way handshake.
This configuration overrides the global session parameters for the configured interface.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | interface
int-if Example: switch(config)# interface ethernet 2/1 switch(config-if)# |
Enters interface configuration mode. Use the ? keyword to display the supported interfaces. |
| Step 3 | bfd interval
mintx
min_rx
msec multiplier
value Example: switch(config-if)# bfd interval 250 min_rx 250 multiplier 3 |
Configures the BFD session parameters for all BFD sessions on the interface. This command overrides the global BFD session parameters. The mintx and msec range is from 250 to 999 milliseconds and the default is 250. The multiplier range is from 3 to 50. The multiplier default is 3. To return to the default settings, use the no bfd interval command. |
| Step 4 | exit Example: switch(config-if)# exit switch (config)# |
Exits interface configuration mode. |
| Step 5 | exit Example: switch (config)# exit switch# |
Exits configuration mode and returns to EXEC mode. |
| Step 6 | show running-config bfd Example: switch# show running-config bfd | (Optional)
Displays the BFD running configuration. |
| Step 7 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring BFD on a Port Channel
You can configure the BFD session parameters for all BFD sessions on a port channel. For example, if the BFD session for one link on a port channel is up, BFD informs client protocols, such as BGP, that the port channel is up. The BFD session parameters are negotiated between the BFD peers in a three-way handshake.
This configuration overrides the global session parameters for the configured port channel. The member ports of the port channel inherit the port channel BFD session parameters, unless you configure subinterface-level BFD parameters on a member port. In that case, the member port subinterface uses the subinterface BFD configuration if subinterface optimization is not enabled. See the Optimizing BFD on Subinterfaces section for more information.
Ensure that you enable LACP on the port channel before you enable BFD.
Enable the BFD feature. See the Enabling the BFD Feature section.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | interface port-channel
number Example: switch(config)# interface port-channel 2 switch(config-if)# |
Enters port channel configuration mode. Use the ? keyword to display the supported number range. |
| Step 3 | bfd interval
mintx
min_rx
msec multiplier
value Example: switch(config-if)# bfd interval 250 min_rx 250 multiplier 3 | (Optional)
Configures the BFD session parameters for all BFD sessions on the interface. This command overrides the global BFD session parameters. The mintx and msec range is from 250 to 999 milliseconds and the default is 250. The multiplier range is from 3 to 50. The multiplier default is 3. To return to the default settings, use the no bfd interval command. |
| Step 4 | exit Example: switch(config-if)# exit switch (config)# |
Exits interface configuration mode. |
| Step 5 | exit Example: switch (config)# exit switch# |
Exits configuration mode and returns to EXEC mode. |
| Step 6 | show running-config bfd Example: switch# show running-config bfd | (Optional)
Displays the BFD running configuration. |
| Step 7 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring the BFD Echo Function
You can configure the BFD echo function on one or both ends of a BFD-monitored link. The echo function slows down the required minimum receive interval, based on the configured slow timer. The RequiredMinEchoRx BFD session parameter is set to zero if the echo function is disabled. The slow timer becomes the required minimum receive interval if the echo function is enabled.
Enable the BFD feature. See the Enabling the BFD Feature section.
Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.
Ensure that Internet Control Message Protocol (ICMP) redirect messages are disabled on BFD-enabled interfaces. Use the no ip redirects command on the interface.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | bfd slow-timer
echo-interval Example: switch(config)# bfd slow-timer 2000 |
Configures the slow timer used in the echo function. This value determines how fast BFD starts up a new session and is used to slow down the asynchrounous sessions when the BFD echo function is enabled. This value overwrites the required minimum receive interval when the echo function is enabled. The range is from 1000 to 30000 milliseconds. The default is 2000. To return to the default settings, use the no bfd slow-timer command. |
| Step 3 | interface
int-if Example: switch(config)# interface ethernet 2/1 switch(config-if)# |
Enters interface configuration mode. Use the ? keyword to display the supported interfaces. |
| Step 4 | bfd echo Example: switch(config-if)# bfd echo |
Enables the echo function. The default is enabled. To disable the echo function, use the no bfd echo command. |
| Step 5 | exit Example: switch(config-if)# exit switch (config)# |
Exits interface configuration mode. |
| Step 6 | exit Example: switch (config)# exit switch# |
Exits configuration mode and returns to EXEC mode. |
| Step 7 | show running-config bfd Example: switch# show running-config bfd | (Optional)
Displays the BFD running configuration. |
| Step 8 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Optimizing BFD on Subinterfaces
You can optimize BFD on subinterfaces. BFD creates sessions for all configured subinterfaces. BFD sets the subinterface with the lowest configured VLAN ID as the master subinterface and that subinterface uses the BFD session parameters of the parent interface. The remaining subinterfaces use the slow timer. If the optimized subinterface session detects an error, BFD marks all subinterfaces on that physical interface as down.
Enable the BFD feature. See the Enabling the BFD Feature section.
Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.
Ensure that these subinterfaces connect to another Cisco NX-OS device. This feature is supported on Cisco NX-OS only.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | interface
int-if Example: switch(config)# interface ethernet 2/1 switch(config-if)# |
Enters interface configuration mode. Use the ? keyword to display the supported interfaces. |
| Step 3 | bfd optimize subinterface Example: switch(config-if)# bfd optimize subinterface |
Optimizes subinterfaces on a BFD-enabled interface. The default is disabled. To disable optimized subinterfaces, use the no bfd optimize subinterfaces command. |
| Step 4 | exit Example: switch(config-if)# exit switch (config)# |
Exits interface configuration mode. |
| Step 5 | exit Example: switch (config)# exit switch# |
Exits configuration mode and returns to EXEC mode. |
| Step 6 | show running-config bfd Example: switch# show running-config bfd | (Optional)
Displays the BFD running configuration. |
| Step 7 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring BFD on BGP
You can configure BFD for the Border Gateway Protocol (BGP).
Enable the BFD feature. See the Enabling the BFD Feature section.
Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | router bgp
as-number Example: switch(config)# router bgp 64496 switch(config-router)# |
Enables BGP and assigns the AS number to the local BGP speaker. The AS number can be a 16-bit integer or a 32-bit integer in the form of a higher 16-bit decimal number and a lower 16-bit decimal number in xx.xx format. |
| Step 3 | neighbor { ip-address } remote-as
as-number Example: switch(config-router)# neighbor 209.165.201.1 remote-as 64497 switch(config-router-neighbor)# |
Configures the IPv4 and AS number for a remote BGP peer. The ip-address format is x.x.x.x. |
| Step 4 | bfd Example: switch(config-router-neighbor)# bfd |
Enables BFD for this BGP peer. |
| Step 5 | show running-config bfd Example: switch# show running-config bfd | (Optional)
Displays the BFD running configuration. |
| Step 6 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring BFD on PIM
You can configure BFD for the Protocol Independent Multicast (PIM) protocol.
Enable the BFD feature. See the Enabling the BFD Feature section.
Enable the PIM feature. See the Cisco Nexus 3548 Switch NX-OS Multicast Routing Configuration Guide for more information.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | ip pim bfd Example: switch(config)# ip pim bfd |
Enables BFD for PIM. |
| Step 3 | interface
type slot/port Example: switch(config)# interface ethernet 2/1 switch(config-if)# |
Enters interface configuration mode. Use the ? keyword to display the supported interfaces. |
| Step 4 | ip pim bfd-instance [ disable ] Example: switch(config-if)# ip pim bfd-instance | (Optional)
Enables or disables BFD on a PIM interface. The default is disabled. |
| Step 5 | show running-config pim Example: switch(config)# show running-config pim | (Optional)
Displays the PIM running configuration. |
| Step 6 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring BFD on OSPFv2
You can configure BFD for the Open Shortest Path First Protocol (OSPFv2).
Enable the BFD feature. See the Enabling the BFD Feature section.
Configure the BFD session parameters. See the Configuring Global BFD Parameters section or the Configuring BFD on an Interface section.
Enable the OSPFv2 feature. See the Enabling the OSPFv2 Feature section.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | router ospf
process-id Example: switch(config)# router ospf 64496 switch(config-router)# |
Creates a new OSPFv2 process with a configured id. |
| Step 3 | bfd Example: switch(config-router)# bfd |
Enables BFD for this OSPFv2 peer. The default value is disabled. |
| Step 4 | interface
int-if Example: switch(config-router)# interface ethernet 1/2 switch (config-if)# |
Enters interface configuration mode. Use the ? keyword to display the supported interfaces. |
| Step 5 | [no] ip ospf bfd disable Example: switch(config-if)# ip ospf bfd disable | (Optional)
Disables BFD on a OSPFv2 interface. The default value is enabled. |
| Step 6 | show running-config ospf Example: switch(config)# show running-config ospf | (Optional)
Displays the OSPFv2 running configuration. |
| Step 7 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Configuring BFD for Static Routes
You can configure BFD for static routes on an interface. You can optionally configure BFD on a static route within a virtual routing and forwarding (VRF) instance.
Enable the BFD feature. See the Enabling the BFD Feature section.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 | configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
| Step 2 | vrf context
vrf-name Example: switch(config)# vrf context Red switch(config-vrf)# | (Optional)
Enters VRF configuration mode. |
| Step 3 | ip route
route interface { nh-address | nh-prefix } Example: switch(config-vrf)# ip route 192.0.2.1 ethernet 2/1 192.0.2.4 |
Creates a static route Use the ? keyword to display the supported interfaces. |
| Step 4 | ip route static bfd
interface { nh-address | nh-prefix } Example: switch(config-vrf)# ip route static bfd ethernet 2/1 192.0.2.4 |
Enables BFD for all static routes on an interface. Use the ? keyword to display the supported interfaces. |
| Step 5 | show ip route static [ vrf
vrf-name ] Example: switch(config-vrf)# show ip route static vrf Red | (Optional)
Displays the static routes. |
| Step 6 | copy running-config startup-config Example: switch# copy running-config startup-config | (Optional)
Saves this configuration change. |
Verifying the BFD Configuration
To display BFD configuration information, perform one of the following tasks:
|
Command |
Purpose |
|---|---|
|
show running-config bfd |
Displays the running BFD configuration. |
|
show startup-config bfd |
Displays the BFD configuration that will be applied on the next system startup. |
For detailed information about the fields in the output from these commands, see the Cisco Nexus 3548 Switch NX-OS Interfaces Command Reference, Release 6.x.
Monitoring BFD
Use the following commands to display BFD:
|
Command |
Purpose |
|---|---|
|
show bfd neighbors [ application name ] [ details ] |
Displays information about BFD for a supported application, such as BGP. |
|
show bfd neighbors [ interface int-if ] [ details ] |
Displays information about BGP sessions on an interface. |
|
show bfd neighbors [ dest-ip ip-address ] [ src-ip ip-address ][ details ] |
Displays information about the specified BGP session on an interface. |
|
show bfd neighbors [ vrf vrf-name ] [ details ] |
Displays information about BFD for a VRF. |
For detailed information about the fields in the output from these commands, see the Cisco Nexus 3548 Switch Command Reference.
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