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  1. Hi,

    what are the disadvantages of using bfd.
    also it would be helpful if you post an article on troubleshooting bfd.

  2. BFD does not work in GNS3. I was using 7200 with IOS 15.x. Checking on forums the consensus is a GNS3 bug. Does anyone have a workaround for this?

    Hostname R1
    !
    interface FastEthernet0/0
     ip address 10.0.0.9 255.255.255.252
     ip ospf 10 area 0
     duplex full
     bfd interval 500 min_rx 500 multiplier 3
    !
    router ospf 10
     router-id 10.0.0.1
     bfd all-interfaces
    

    -

    Hostname R2
    !
    interface FastEthernet0/0
     ip address 10.0.0.10 255.255.255.252
     ip ospf 10 area 0
     duplex full
     bfd interval 500 min_rx 500 multiplier 3
    !
    router ospf 10
     router-id 10.0.0.1
     bfd all-interfaces
    

    -

    R1#ping 10.0.0.10 repeat 10
    Type escape sequence to abort.
    Sending 10, 100-byte ICMP Echos to 10.0.0.10, timeout is 2 seconds:
    !!!!!!!!!!
    Success rate is 100 percent (10/10), round-trip min/avg/max = 20/20/20 ms
    

    -

    R2#ping 10.0.0.9 repeat 10
    Type escape sequence to abort.
    Sending 10, 100-byte ICMP Echos to 10.0.0.9, timeout is 2 seconds:
    !!!!!!!!!!
    Success rate is 100 percent (10/10), round-trip min/avg/max = 8/12/20 ms
    

    -

    R1#
    *Feb 27 09:11:39.335: %SCHED-5-INT_DISABLED_BEFORE_PREEMPTION: Detected interrupts being disabled in preemption handler. schedflag = (1)  forkx = (EnvMon)  preempted process = (<Null>) preempted_process_epc = (0x63267C7C) preemption_forced_suspend_level = (1) current interrupt level = (0)  getinterruptindex() = (0) onintstack() = (FALSE)
    -Traceback=
    

    -

    R2#
    *Feb 27 09:11:26.863: %SCHED-5-INT_DISABLED_BEFORE_PREEMPTION: Detected interrupts being disabled in preemption handler. schedflag = (1)  forkx = (BFD PP Process)  preempted process = (<Null>) preempted_process_epc = (0x63267C7C) preemption_forced_suspend_level = (1) current interrupt level = (0)  getinterruptindex() = (0) onintstack() = (FALSE)
    -Traceback=
  3. Hi @tadeosho70,

    With echo mode, this is no problem. The packets you send are echoed back to you. For example, take a look at this output:

    R1(config)#interface FastEthernet 0/0
    R1(config-if)#bfd interval 300 min_rx 300 multiplier 3 
    
    R2(config)#interface FastEthernet 0/0
    R2(config-if)#bfd interval 300 min_rx 600 multiplier 3 
    

    The min_rx is set to 300 on R1 and 600 on R2. Here’s the output of R1 showing the 600 ms of R2:

    R1#show bfd neighbors details 
    
    NeighAddr                         LD/RD    RH/RS     State     Int
    192.168.12.2                       1/1     Up        Up        Fa0/0
    Session state is UP and using echo function with 600 ms interval.
    OurAddr: 192.168.12.1   
    Local Diag: 0, Demand mode: 0, Poll bit: 0
    MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
    Received MinRxInt: 1000000, Received Multiplier: 3
    Holddown (hits): 0(0), Hello (hits): 1000(571)
    Rx Count: 578, Rx Interval (ms) min/max/avg: 1/1000/867 last: 396 ms ago
    Tx Count: 580, Tx Interval (ms) min/max/avg: 1/1000/865 last: 276 ms ago
    Elapsed time watermarks: 0 0 (last: 0)
    Registered protocols: OSPF
    Uptime: 00:08:21
    Last packet: Version: 1                  - Diagnostic: 0
                 State bit: Up               - Demand bit: 0
                 Poll bit: 0                 - Final bit: 0
                 Multiplier: 3               - Length: 24
                 My Discr.: 1                - Your Discr.: 1
                 Min tx interval: 1000000    - Min rx interval: 1000000
                 Min Echo interval: 600000 
    

    and R2:

    R2#show bfd neighbors details 
    
    NeighAddr                         LD/RD    RH/RS     State     Int
    192.168.12.1                       1/1     Up        Up        Fa0/0
    Session state is UP and using echo function with 300 ms interval.
    OurAddr: 192.168.12.2   
    Local Diag: 0, Demand mode: 0, Poll bit: 0
    MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
    Received MinRxInt: 1000000, Received Multiplier: 3
    Holddown (hits): 0(0), Hello (hits): 1000(575)
    Rx Count: 584, Rx Interval (ms) min/max/avg: 1/1000/865 last: 700 ms ago
    Tx Count: 583, Tx Interval (ms) min/max/avg: 1/1000/868 last: 12 ms ago
    Elapsed time watermarks: 0 0 (last: 0)
    Registered protocols: OSPF
    Uptime: 00:08:25
    Last packet: Version: 1                  - Diagnostic: 0
                 State bit: Up               - Demand bit: 0
                 Poll bit: 0                 - Final bit: 0
                 Multiplier: 3               - Length: 24
                 My Discr.: 1                - Your Discr.: 1
                 Min tx interval: 1000000    - Min rx interval: 1000000
                 Min Echo interval: 300000 
    

    Keep in mind that your own packets are echoed back to you, it’s not like OSPF or EIGRP where you need to receive a hello packet from your neighbor.

  4. Thanks Lagapides

    It is very helpful

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