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How to configure and verify Bidirectional Forward Detection (BFD) settings under Open Shortest Path First protocol stanza on EX Switches



Article ID: KB15095 KB Last Updated: 08 Sep 2009Version: 1.0
The Bidirectional Forward Detection (BFD) protocol is a simple hello mechanism that detects failures in a network. Hello packets are sent at a regular specified intervals. A neighbor failure is detected when the router stops recieving a reply after the specified interval. The failure detection timers for BFD have shorter time limits than default failure detection mechanisms, providing faster detection. These timers are also adaptive and can be adjusted to be more or less aggressive. For example, the timers can adapt to a higher value if the adjacency fails, or a neighbor can negotiate a higher value for a timer than the one configured. This KB explains how to configure and verify BFD under OSPF protocol.



To enable BFD under OSPF, include the bfd-liveness-detection statement under edit protocols ospf on the interface where the neighbor is connected.

Sample configuration:
  1. Configure the bfd timer minimum-interval to specify the transmit and receive intervals on the interface where the ospf neighbor is connected                 
[edit protocols ospf area]
              user@switch# set interface ge-0/0/20.0 bfd-liveness-detection minimum-interval 500
  1. Configure the multiplier number which is the number of hello packets not received by a neighbor that causes the originating interface to be declared down

           [edit protocols ospf area]
       user@switch# set interface ge-0/0/2.0 bfd-liveness-detection multiplier 3

        3.  Configure BFD sessions only for the OSPF neighbors with full neighborship adjacency. The default behavior is to establish BFD sessions for all OSPF neighbors.

This feature is applicable only from JUNOS 9.5 release and higher.

               [edit protocols ospf area]
      user@switch# set interface ge-0/0/20.0 bfd-liveness-detection full-neighbors-only
The "show bfd session extensive" command shows the bfd session between the two routers with ospf adjacency:

         juniper@switch> show bfd session extensive

         Detect Transmit
         Address State Interface Time Interval Multiplier Up ge-0/0/20.0 1.500 0.500 3
         Client OSPF realm ospf-v2 Area, TX interval 0.500, RX interval 0.500
         Session up time 4d 03:44
         Local diagnostic None, remote diagnostic NbrSignal
         Remote state Up, version 1
         Min async interval 0.500, min slow interval 1.000
         Adaptive async TX interval 0.500, RX interval 0.500
         Local min TX interval 0.500, minimum RX interval 0.500, multiplier 3
         Remote min TX interval 0.500, min RX interval 0.500, multiplier 3
         Local discriminator 1, remote discriminator 10
         Echo mode disabled/inactive
         1 sessions, 1 clients
         Cumulative transmit rate 2.0 pps, cumulative receive rate 2.0 pps
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