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