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.


Note

Cisco NCS 5000 Routers do not support BFD dampening. If it is enabled by default, disable it first before configuring any session. If dampening is disabled after configuring the BFD session, reload the device for it to take effect.

BFD over Bundle

BFD over Bundle feature enables BFD sessions to monitor the status of individual bundle member links. BFD notifies the bundle manager immediately when one of the member links goes down, and reduces the bandwidth used by the bundle.

Restrictions

The following are the restrictions in using BFD over Bundle feature:

  • It is only supported in IETF mode.

  • It is only supported on main bundle interface; it is not supported on bundle sub-interfaces.

  • It is not supported on routing protocols, such as OSPF, ISIS, and BGP.

  • When BFD timer is configured to 3.3 ms, which is the most aggressive timer, 256 sessions can be brought up.

  • If BFD timer is configured to greater than 100 ms, 300 BFD sessions can be brought up simultaneously.

  • BFD echo mode and encryption is not supported.

  • BFD dampening is not supported.

Configure BFD over Bundle

Configuring BFD over bundle involves the following steps:

  • Enable and Disable IPv6 checksum calculations for BFD on a router

  • Specify the mode, BFD packet transmission intervals, and failure detection times on a bundle


Note

Repeat the same configuration steps in the destination router. 


/* Enable and Disable IPv6 checksum calculations for BFD on a router. */

Router(config-if)# bfd
Router(config-bfd-if)# ipv6 checksum disable 
Router(config-bfd-if)# dampening disable
Router(config-bfd-if)# commit

/* Specify the mode, BFD packet transmission intervals, and failure detection times on a bundle */

Router(config)# interface Bundle-Ether 3739
Router(config-if)# bfd mode ietf
Router(config-if)# bfd address-family ipv4 multiplier 3
Router(config-if)# bfd address-family ipv4 destination 10.23.1.2
Router(config-if)# bfd address-family ipv4 fast-detect
Router(config-if)# bfd address-family ipv4 minimum-interval 100
Router(config-if)# bfd address-family ipv6 multiplier 3
Router(config-if)# bfd address-family ipv6 destination 2001:DB8:1::2
Router(config-if)# bfd address-family ipv6 fast-detect
Router(config-if)# bfd address-family ipv6 minimum-interval 100
Router(config-if)# ipv4 address 10.23.1.1 255.255.255.252
Router(config-if)# ipv6 address 2001:DB8:1::2/120
Router(config-if)# load-interval 30
Router(config-if)# commit
Router(config)# interface TenGigE 0/0/0/0
Router(config-if)# bundle id 3739 mode active

Running Configuration 


bfd
 ipv6 checksum disable 
 dampening disable!
 !

interface Bundle-Ether3739
 bfd mode ietf
 bfd address-family ipv4 multiplier 3
 bfd address-family ipv4 destination 10.23.1.2
 bfd address-family ipv4 fast-detect
 bfd address-family ipv4 minimum-interval 100
 bfd address-family ipv6 multiplier 3
 bfd address-family ipv6 destination 2001:DB8:1::2
 bfd address-family ipv6 fast-detect
 bfd address-family ipv6 minimum-interval 100
 ipv4 address 10.23.1.1 255.255.255.252
 ipv6 address 2001:DB8:1::2/120
 load-interval 30
 !

interface TenGigE 0/0/0/0
 bundle id 3739 mode active

Verification

The following show command outputs displays the status of BFD sessions on bundle members: 


/* Verify the details of the IPv4 BFD session in the source router. */

Router# show bfd session

Interface  Dest Addr  Local det time(int*mult)  State  Echo  Async   H/W   NPU
---------  ---------  --------  -------------   -----  ----  -----   ---   ---
Te0/0/0/0  10.23.1.2  0s(0s*0)  300ms(100ms*3)  UP     Yes                0/RP0/CPU0
BE3739     10.23.1.2  n/a       n/a             UP     No    n/a


/* Verify the details of the IPv4 BFD session in the destination router. */

Router# show bfd session

Interface   Dest Addr  Local det  time(int*mult) State   Echo   Async   H/W   NPU
----------  ---------- --------   -------------- -----  ----   -----   ---   ---
Te0/6/0/0   10.23.1.1  0s(0s*0)   300ms(100ms*3) UP      No     n/a
BE3739      10.23.1.1  n/a        n/a            UP      No     n/a


/* Verify the details of the IPv6 BFD session in the source router. */

Router# show bfd ipv6 session
Interface  Dest Addr  Local det  time(int*mult) State      H/W     NPU       Echo Async
---------- ---------- ---------- -------------- ------     ------  ------    ---- ----
Te0/0/0/0  10:23:1::2 Yes                       0/RP0/0s (0s*0) 00ms(100ms*3) UP

BE3739     10:23:1::2 No                        n/a        n/a      n/a       UP

/* Verify the details of the IPv6 BFD session in the destination router. */

Router# show bfd ipv6 session
Interface  Dest Addr  Local det time(int*mult) State    H/W NPU           Echo  Async 
---------- ---------- --------- -------------- -------  --- ---           ----  ----
Te0/6/0/0  10:23:1::1 No        n/a            0s(0s*0)     300ms(100ms*3)  UP
BE3739     10:23:1::1 No        n/a            n/a          n/a             UP

BFD over Bundle and BFD over Logical Bundle

Link Aggregation Control Protocol (LACP) allows a network device to negotiate an automatic bundling of links by sending LACP packets to their directly connected peer. LACP provides a keep-alive mechanism for the link members. While the default keep-alive is 30s, it is configurable to up to 1s. LACP can detect failures on a per-physical-member link. However, the LACP timers do not fulfill the criteria of current fast convergence requirements.

Differences between BFD over Bundle and BFD over Logical Bundle

BFD over Bundle (BoB) (RFC 7130) has a BFD session on each bundle member. The client is the bundle manager. If a BFD session goes down on a specific member link, the whole bundle interface goes down. That is, when the member link goes down, the number of available links falls below the required minimum. Hence the routing session is brought down.

BFD over Logical Bundle (BLB) (RFC 5880) treats a bundle interface with all its members as a single interface. BLB is a multipath (MP) single-hop session. If BLB is configured on a bundle there is only one single BFD session that is active. This implies that only one bundle member is being monitored by BFD at any given time. The client is one of the routing protocols. When BFD detects a failure, the client brings down the routing session.

The mode (BoB or BLB) is determined by how you configure BFD:

  • You can enable BoB by configuring BFD under a Bundle-Ether interface.

  • You can enable BLB by configuring BFD under a Bundle-Ether interface on a routing client.

Link Aggregation Control Protocol (LACP) allows a network device to negotiate an automatic bundling of links by sending LACP packets to their directly connected peer. LACP provides a keep-alive mechanism for the link members. While the default keep-alive is 30s, it is configurable to up to 1s. LACP can detect failures on a per-physical-member link. However, the LACP timers do not fulfill the criteria of current fast convergence requirements.

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

  Command or Action Purpose
Step 1

configure

Example:


RP/0/RP0/CPU0:router# 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 fast-detect

Example:


RP/0/RP0/CPU0: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.

Specifying the BFD Destination Address on a Bundle

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

SUMMARY STEPS

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

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Example:


RP/0/RP0/CPU0:router# 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.

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:

SUMMARY STEPS

  1. configure
  2. interface Bundle-Ether bundle-id
  3. bundle minimum-active bandwidth kbps
  4. bundle minimum-active links links
  5. Use the commit or end command.

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Example:


RP/0/RP0/CPU0:router# 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

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

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 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:

SUMMARY STEPS

  1. configure
  2. interface Bundle-Ether bundle-id
  3. bfd address-family ipv4 minimum-interval milliseconds
  4. bfd address-family ipv4 multiplier multiplier
  5. Use the commit or end command.

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Example:


RP/0/RP0/CPU0:router# 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 minimum-interval milliseconds

Example:


RP/0/RP0/CPU0:router(config-if)#bfd address-family ipv4 minimum-interval 2000
Note 
Specifies the minimum interval, in milliseconds, for asynchronous mode control packets on IPv4 BFD sessions on bundle member links. The range is from 4 to 30000.
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. The range is from 2 to 50. The default is 3.

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

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:

SUMMARY STEPS

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

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Example:


RP/0/RP0/CPU0:router# 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 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

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.

Step 6

show bundle bundle-ether bundle-id

Displays the selected bundle mode.