Troubleshoot Bidirectional Forwarding Detection in Cisco IOS XE

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Updated:April 6, 2023

Document ID:220364

Bias-Free Language

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BFD Modes of Operation

Troubleshoot BFD Problems

BFD Down

BFD Neighbor Flaps

Neighbor Flaps Due to Packet Loss

Neighbor Flaps Due to Parameters Set Too Low

BFD Does Not Fail Over When Strict Mode is Not Configured

Useful Show Commands

Show BFD Neighbor Details

Show BFD Summary

Show BFD Drops

Show BFD Neighbors History

Related Information

Introduction

This document describes how to troubleshoot issues with Bidirectional Forwarding Detection (BFD) in Cisco IOS® XE.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software or hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

BFD Overview

Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forward path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forward path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forward path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiles and plans are easier, and reconvergence time is consistent and predictable.

A pair of systems transmit BFD packets periodically over each path between the two systems, and if a system stops receipt of BFD packets for long enough, some component in that particular bidirectional path to the neighbor system is assumed to have failed. Under some conditions, systems can negotiate not to send periodic BFD packets in order to reduce overhead. Reduction of number and frequency of updates can, however, impact the sensitivity of BFD.

The image shows BFD establishment in simple network with two routers configured for OSPF and BFD. When OSPF discovers a neighbor (1) it sends a request to the local BFD process to initiate a BFD neighbor session with the OSPF neighbor router (2). The BFD neighbor session with the OSPF neighbor router is established (3). The same progression is used with other routing protocols when BFD is enabled.

Basic BFD

BFD Modes of Operation

BFD Echo Mode - Echo mode is enabled by default, and runs with asynchronous BFD. It can be disabled on one side to run with asymmetry, or run on both sides of a neighborship. Echo packets are sent by the forward engine, and forwarded back along the same path. An echo packet is set with a source and destination address of the interface itself, and a destination UDP port of 3785. The neighbor reflects the echo back to the originator, which minimizes its process load of the packet, and increases the possible sensitivity of BFD. In general, echoes are not forwarded to the control plane of the neighbor, in order to reduce delays and CPU load.

BFD Asynchronous Mode - Asynchonous mode tracks the neighbor availability by the exchange of control packets between the two neighbors, which requires static configuration of BFD on both sides.

Troubleshoot BFD Problems

BFD Down

BFD down log messages are crucial to isolation of a down session. There are several different causes which can be seen:

DETECT TIMER EXPIRED - The router no longer receives BFD keepalive traffic and times out.

ECHO FAILURE - The router no longer receives its BFD echos from the other side.

RX DOWN - The router receives notification from its neighbor that it has gone down.

RX ADMINDOWN - BFD has been disabled on the neighbor device.

*Mar 31 19:35:51.809: %BFDFSM-6-BFD_SESS_DOWN: BFD-SYSLOG: BFD session ld:4111 handle:3,is going Down Reason: RX DOWN
*Mar 31 19:35:51.811: %BGP-5-NBR_RESET: Neighbor 10.1.1.2 reset (BFD adjacency down)
*Mar 31 19:35:51.812: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Down BFD adjacency down
*Mar 31 19:35:51.813: %BGP_SESSION-5-ADJCHANGE: neighbor 10.1.1.2 IPv4 Unicast topology base removed from session  BFD adjacency down
*Mar 31 19:35:51.813: %BFD-6-BFD_SESS_DESTROYED: BFD-SYSLOG: bfd_session_destroyed,  ld:4111 neigh proc:BGP, handle:3 active


*Mar 31 19:36:33.377: %BFDFSM-6-BFD_SESS_DOWN: BFD-SYSLOG: BFD session ld:4113 handle:1,is going Down Reason: ECHO FAILURE
*Mar 31 19:36:33.380: %BFD-6-BFD_SESS_DESTROYED: BFD-SYSLOG: bfd_session_destroyed,  ld:4113 neigh proc:OSPF, handle:1 active
*Mar 31 19:36:33.381: %OSPF-5-ADJCHG: Process 1, Nbr 10.30.30.30 on GigabitEthernet3 from FULL to DOWN, Neighbor Down: BFD node down


*Mar 31 19:35:59.483: %BFDFSM-6-BFD_SESS_DOWN: BFD-SYSLOG: BFD session ld:4110 handle:2,is going Down Reason: RX ADMINDOWN
*Mar 31 19:36:02.220: %BFD-6-BFD_SESS_CREATED: BFD-SYSLOG: bfd_session_created, neigh 10.1.1.2 proc:BGP, idb:GigabitEthernet1 handle:3 act

After confirmation of the reason the BFD session is torn down, and the directionality of the problem, you can begin to isolate possible causes:

One-way media failure
Configuration changes
BFD blocked in the path
CPU or forward failures on one device

BFD Neighbor Flaps

Neighbor Flaps Due to Packet Loss

Frequent BFD flaps can often be due to a lossy link that causes BFD control packets or echos to be lost. If there are multiple different session down reasons, this would be more indicative of packet loss.

*Apr  4 17:18:25.931: %BFDFSM-6-BFD_SESS_DOWN: BFD-SYSLOG: BFD session ld:4097 handle:1,is going Down Reason: RX DOWN
*Apr  4 17:18:25.933: %BGP-5-NBR_RESET: Neighbor 10.1.1.2 reset (BFD adjacency down)
*Apr  4 17:18:25.934: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Down BFD adjacency down
*Apr  4 17:18:25.934: %BGP_SESSION-5-ADJCHANGE: neighbor 10.1.1.2 IPv4 Unicast topology base removed from session  BFD adjacency down
*Apr  4 17:18:25.934: %BFD-6-BFD_SESS_DESTROYED: BFD-SYSLOG: bfd_session_destroyed,  ld:4097 neigh proc:BGP, handle:1 active
*Apr  4 17:18:27.828: %BFDFSM-6-BFD_SESS_UP: BFD-SYSLOG: BFD session ld:4097 handle:1 is going UP
*Apr  4 17:18:32.304: %BFD-6-BFD_SESS_CREATED: BFD-SYSLOG: bfd_session_created, neigh 10.1.1.2 proc:BGP, idb:GigabitEthernet1 handle:1 act
*Apr  4 17:18:32.304: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Up 
*Apr  4 17:18:34.005: %BFDFSM-6-BFD_SESS_UP: BFD-SYSLOG: BFD session ld:4100 handle:1 is going UP
*Apr  4 17:18:34.418: %BFDFSM-6-BFD_SESS_DOWN: BFD-SYSLOG: BFD session ld:4100 handle:1,is going Down Reason: ECHO FAILURE
*Apr  4 17:18:34.420: %BGP-5-NBR_RESET: Neighbor 10.1.1.2 reset (BFD adjacency down)
*Apr  4 17:18:34.422: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Down BFD adjacency down
*Apr  4 17:18:34.422: %BGP_SESSION-5-ADJCHANGE: neighbor 10.1.1.2 IPv4 Unicast topology base removed from session  BFD adjacency down
*Apr  4 17:18:34.422: %BFD-6-BFD_SESS_DESTROYED: BFD-SYSLOG: bfd_session_destroyed,  ld:4100 neigh proc:BGP, handle:1 active
*Apr  4 17:18:42.529: %BFD-6-BFD_SESS_CREATED: BFD-SYSLOG: bfd_session_created, neigh 10.1.1.2 proc:BGP, idb:GigabitEthernet1 handle:1 act
*Apr  4 17:18:42.529: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Up 
*Apr  4 17:18:43.173: %BFDFSM-6-BFD_SESS_UP: BFD-SYSLOG: BFD session ld:4100 handle:1 is going UP

To isolate packet loss, it is helpful to take an embedded packet capture of the involved interface. The basic commands are:

monitor capture <name> interface <interface> <in|out|both>
monitor capture <name> match ipv4 protocol udp any any eq <3784|3785>

You can also filter with an access-list to match both BFD control and echo packets.

config t
ip access-list extended <ACLname>
permit udp any any eq 3784
permit udp any any eq 3785
end
monitor capture <name> interface <interface> <in|out|both>
monitor capture <name> access-list <ACLname>

In this example, captures on the inbound interface show BFD control packets are received consistently, but echoes are intermittent. From the 5 second to 15 second timestamps, there are no echo packets for the local system 10.1.1.1 seen returned. This would indicate there is loss from the BFD router towards its neighbor.

BFDrouter#show run | section access-list extended
ip access-list extended BFDcap
 10 permit udp any any eq 3784
 20 permit udp any any eq 3785
BFDrouter#mon cap BFD interface Gi1 in
BFDrouter#mon cap BFD access-list BFDcap
BFDrouter#mon cap BFD start
Started capture point : BFD
BFDrouter#mon cap BFD stop
Stopped capture point : BFD
BFDrouter#show mon cap BFD buffer brief
 ----------------------------------------------------------------------------
 #   size   timestamp     source	     destination      dscp    protocol
 ----------------------------------------------------------------------------
...
 212   54    4.694016   10.1.1.1         ->  10.1.1.1         48 CS6  UDP
 213   54    4.733016   10.1.1.2         ->  10.1.1.2         48 CS6  UDP
 214   54    4.735014   10.1.1.1         ->  10.1.1.1         48 CS6  UDP
 215   54    4.789012   10.1.1.1         ->  10.1.1.1         48 CS6  UDP
 216   54    4.808009   10.1.1.2         ->  10.1.1.2         48 CS6  UDP
 217   54    4.838006   10.1.1.1         ->  10.1.1.1         48 CS6  UDP
 218   66    4.857002   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 219   66    5.712021   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 220   66    6.593963   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 221   66    7.570970   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 222   66    8.568971   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 223   66    9.354977   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 224   66   10.250979   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 225   66   11.154991   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 226   66   11.950000   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 227   66   12.925007   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 228   66   13.687013   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 229   66   14.552965   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 230   66   15.537967   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 231   66   15.641965   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 232   66   15.656964   10.1.1.2         ->  10.1.1.1         48 CS6  UDP
 233   54   15.683015   10.1.1.1         ->  10.1.1.1         48 CS6  UDP
 234   54   15.702011   10.1.1.2         ->  10.1.1.2         48 CS6  UDP
 235   54   15.731017   10.1.1.1         ->  10.1.1.1         48 CS6  UDP
 236   54   15.752012   10.1.1.2         ->  10.1.1.2         48 CS6  UDP

Neighbor Flaps Due to Parameters Set Too Low

On lower speed links, it is important to be mindful of approriate BFD parameters. The interval and minimum receive values are set in milliseconds. If the delay between neighbors is at or near these values, normal delays caused by traffic conditions trigger BFD flaps. For example, if the normal end-to-end delay between neighbors is 100 ms and the BFD interval is set to the minimum of 50 ms with a multiplier of 3, a single missed BFD packet would trigger a neighbor down event, as the next two are still in transit.

You can validate the delay to the neighbor via a simple ping between the two neighbor IP addresses.

Additonally, the minimum supported timers vary per-platform, and must be confirmed prior to BFD configuration.

BFD Does Not Fail Over When Strict Mode is Not Configured

It is important to note that when BFD strict-mode is not enabled, the absence of a BFD session does not prevent the associated routing protocol from establishment.

This can allow re-convergence in undesirable scenarios. In the example, BFD successfully tears down BGP, but because TCP communication remains successful, the neighbor comes back up.

*Mar 31 18:53:08.997: %BFDFSM-6-BFD_SESS_DOWN: BFD-SYSLOG: BFD session ld:4097 handle:1,is going Down Reason: DETECT TIMER EXPIRED
*Mar 31 18:53:08.999: %BGP-5-NBR_RESET: Neighbor 10.1.1.1 reset (BFD adjacency down)
*Mar 31 18:53:09.000: %BGP-5-ADJCHANGE: neighbor 10.1.1.1 Down BFD adjacency down
*Mar 31 18:53:09.000: %BGP_SESSION-5-ADJCHANGE: neighbor 10.1.1.1 IPv4 Unicast topology base removed from session  BFD adjacency down^Z
BGPpeer#
*Mar 31 18:53:09.000: %BFD-6-BFD_SESS_DESTROYED: BFD-SYSLOG: bfd_session_destroyed,  ld:4097 neigh proc:BGP, handle:1 active
*Mar 31 18:53:10.044: %SYS-5-CONFIG_I: Configured from console by console
BGPpeer#
*Mar 31 18:53:15.245: %BFD-6-BFD_SESS_CREATED: BFD-SYSLOG: bfd_session_created, neigh 10.1.1.1 proc:BGP, idb:GigabitEthernet1 handle:1 act
*Mar 31 18:53:15.245: %BGP-5-ADJCHANGE: neighbor 10.1.1.1 Up 
BGPpeer#show bfd neighbor

IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
10.1.1.1                             4097/0          Down      Down      Gi1

Because BGP is up prior to BFD neighborship, the network re-converges. If BFD remains down, the only way for the neighbor to be brought down is when the two minute hold timer expires, which delays failover.

*Mar 31 18:59:01.539: %BGP-3-NOTIFICATION: sent to neighbor 10.1.1.1 4/0 (hold time expired) 0 bytes 
*Mar 31 18:59:01.540: %BGP-5-NBR_RESET: Neighbor 10.1.1.1 reset (BGP Notification sent)
*Mar 31 18:59:01.541: %BGP-5-ADJCHANGE: neighbor 10.1.1.1 Down BGP Notification sent
*Mar 31 18:59:01.541: %BGP_SESSION-5-ADJCHANGE: neighbor 10.1.1.1 IPv4 Unicast topology base removed from session  BGP Notification sent
*Mar 31 18:59:01.541: %BFD-6-BFD_SESS_DESTROYED: BFD-SYSLOG: bfd_session_destroyed,  ld:4097 neigh proc:BGP, handle:1 active

Useful Show Commands

Show BFD Neighbor Details

This command provides details of the configured BFD neighbors as outlined below. This includes all neighbors independent of current state.

BFDrouter#show bfd neighbor details

IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
10.1.1.2                             4104/4097       Up        Up        Gi1
Session state is UP and using echo function with 50 ms interval.
Session Host: Software
OurAddr: 10.1.1.1       
Handle: 3
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(36)
Rx Count: 38, Rx Interval (ms) min/max/avg: 2/1001/827 last: 493 ms ago
Tx Count: 39, Tx Interval (ms) min/max/avg: 4/988/809 last: 402 ms ago
Echo Rx Count: 534, Echo Rx Interval (ms) min/max/avg: 23/68/45 last: 26 ms ago
Echo Tx Count: 534, Echo Tx Interval (ms) min/max/avg: 39/63/45 last: 27 ms ago
Elapsed time watermarks: 0 0 (last: 0)
Registered protocols: BGP CEF 
Uptime: 00:00:24
Last packet: Version: 1                  - Diagnostic: 0
             State bit: Up               - Demand bit: 0
             Poll bit: 0                 - Final bit: 0
             C bit: 0                                   
             Multiplier: 3               - Length: 24
             My Discr.: 4097             - Your Discr.: 4104
             Min tx interval: 1000000    - Min rx interval: 1000000
             Min Echo interval: 50000   

IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
10.2.2.2                             4102/4097       Up        Up        Gi2
Session state is UP and using echo function with 50 ms interval.
Session Host: Software
OurAddr: 10.2.2.1       
Handle: 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(2637)
Rx Count: 2639, Rx Interval (ms) min/max/avg: 3/1012/879 last: 10 ms ago
Tx Count: 2639, Tx Interval (ms) min/max/avg: 2/1006/879 last: 683 ms ago
Echo Rx Count: 51504, Echo Rx Interval (ms) min/max/avg: 1/98/45 last: 32 ms ago
Echo Tx Count: 51504, Echo Tx Interval (ms) min/max/avg: 39/98/45 last: 34 ms ago
Elapsed time watermarks: 0 0 (last: 0)
Registered protocols: EIGRP CEF 
Uptime: 00:38:37
Last packet: Version: 1                  - Diagnostic: 0
             State bit: Up               - Demand bit: 0
             Poll bit: 0                 - Final bit: 0
             C bit: 0                                   
             Multiplier: 3               - Length: 24
             My Discr.: 4097             - Your Discr.: 4102
             Min tx interval: 1000000    - Min rx interval: 1000000
             Min Echo interval: 50000   

IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
10.3.3.2                             4100/4097       Up        Up        Gi3
Session state is UP and using echo function with 50 ms interval.
Session Host: Software
OurAddr: 10.3.3.1       
Handle: 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(10120)
Rx Count: 10137, Rx Interval (ms) min/max/avg: 1/2761/878 last: 816 ms ago
Tx Count: 10136, Tx Interval (ms) min/max/avg: 1/2645/877 last: 904 ms ago
Echo Rx Count: 197745, Echo Rx Interval (ms) min/max/avg: 1/4126/45 last: 15 ms ago
Echo Tx Count: 197745, Echo Tx Interval (ms) min/max/avg: 39/4227/45 last: 16 ms ago
Elapsed time watermarks: 0 0 (last: 0)
Registered protocols: CEF OSPF 
Uptime: 00:38:39
Last packet: Version: 1                  - Diagnostic: 0
             State bit: Up               - Demand bit: 0
             Poll bit: 0                 - Final bit: 0
             C bit: 0                                   
             Multiplier: 3               - Length: 24
             My Discr.: 4097             - Your Discr.: 4100
             Min tx interval: 1000000    - Min rx interval: 1000000
             Min Echo interval: 50000

Key Fields:

Session Host	This field specifies if the session is hosted in software or offloaded to hardware. Hardware offload is available on some platforms to prevent BFD instability due to CPU congestion.
MinTxInt/MinRxInt/Multiplier	The local values for minimum transmit and receive intervals and multiplier
Received MinRxInt/Received Multiplier	The peer values for minimum receive interval and multiplier
Rx/Tx Count	Counters of the sent and received BFD packets
Echo Rx/Tx Count	Counters for sent and received BFD Echoes
Registered Protocols	Routing protocol used by the BFD session
Uptime	Session uptime
LD/RD	Local Discriminator and Remote Discriminator for the session
RH/RS	Remote Heard and Remote State

Show BFD Summary

The show bfd summary command provides multiple quick outputs of the active client protocols, IP protocol sessions, or hardware vs software hosted BFD sessions. This information is useful when the output of the full details is long and unwieldy.

BFDrouter#show bfd summary client

Client              Session          Up          Down
BGP                       1           1             0
EIGRP                     1           1             0
OSPF                      1           1             0
CEF                       3           3             0

Total                     3           3             0
BFDrouter#show bfd summary session

Protocol            Session          Up          Down
IPV4                      3           3             0

Total                     3           3             0

BFDrouter#show bfd summary host

Host              Session          Up          Down
Software                  3           3             0
Hardware                  0           0             0

Total                     3           3             0

Show BFD Drops

This command shows BFD packets dropped on the local device and the reason. If local drops are incremented, this can cause sessions to flap.

BFDrouter#show bfd drops
BFD Drop Statistics
                        IPV4    IPV6    IPV4-M  IPV6-M  MPLS_PW MPLS_TP_LSP MPLS_TE_GAL_LSP MPLS_TE_SR_LSP POCH_IPV4
Invalid TTL             0        0       0       0       0       0              0                   0           0
BFD Not Configured      0        0       0       0       0       0              0                   0           0
No BFD Adjacency        12       0       0       0       0       0              0                   0           0
Invalid Header Bits     0        0       0       0       0       0              0                   0           0
Invalid Discriminator   3        0       0       0       0       0              0                   0           0
Session AdminDown       2222     0       0       0       0       0              0                   0           0
Authen invalid BFD ver  0        0       0       0       0       0              0                   0           0
Authen invalid len      0        0       0       0       0       0              0                   0           0
Authen invalid seq      0        0       0       0       0       0              0                   0           0
Authen failed           0        0       0       0       0       0              0                   0           0
Dampenend Down          0        0       0       0       0       0              0                   0           0
SBFD Srcip Invalid      0        0       0       0       0       0              0                   0           0
Invalid SBFD_SPORT      0        0       0       0       0       0              0                   0           0
Source Port not valid   0        0       0       0       0       0              0                   0           0

Show BFD Neighbors History

This command shows recent BFD logs for each neighbor, along with its present state.

BFDrouter#  show bfd neighbors history

IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
10.1.1.2                             4101/4097       Down      Init      Gi1
History information:
[Apr  4 15:56:21.346] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:20.527] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:19.552] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:18.776] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:17.823] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:16.816] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:15.886] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:14.920] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:14.023] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:13.060] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:12.183] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:11.389] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:10.600] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:09.603] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:08.750] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:07.808] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:06.825] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:05.877] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
[Apr  4 15:56:04.917] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT
[Apr  4 15:56:03.920] Event: V1 FSM ld:4101 handle:3 event:RX DOWN state:INIT

10.2.2.2                              104/4097       Up        Up        Gi2
History information:
[Apr  4 15:10:41.820] Event: V1 FSM ld:104 handle:1 event:RX UP state:UP
[Apr  4 15:10:41.803] Event: V1 FSM ld:104 handle:1 event:RX UP state:UP
[Apr  4 15:10:41.784] Event: V1 FSM ld:104 handle:1 event:RX UP state:UP
[Apr  4 15:10:41.770] Event: notify client(CEF) IP:10.2.2.2, ld:104, handle:1, event:UP, 
[Apr  4 15:10:41.770] Event: notify client(EIGRP) IP:10.2.2.2, ld:104, handle:1, event:UP, 
[Apr  4 15:10:41.770] Event: notify client(CEF) IP:10.2.2.2, ld:104, handle:1, event:UP, 
[Apr  4 15:10:41.770] Event: resetting timestamps ld:104 handle:1
[Apr  4 15:10:41.768] Event: V1 FSM ld:104 handle:1 event:RX INIT state:DOWN
[Apr  4 15:10:41.751] Event: V1 FSM ld:104 handle:1 event:Session create state:DOWN
[Apr  4 15:10:41.751] 
 bfd_session_created, proc:EIGRP, idb:GigabitEthernet2 handle:1 act 

10.3.3.2                             4198/4097       Up        Up        Gi3
History information:
IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
[Apr  4 15:26:01.779] Event: notify client(CEF) IP:10.3.3.2, ld:4198, handle:2, event:UP, 
[Apr  4 15:26:01.779] Event: notify client(OSPF) IP:10.3.3.2, ld:4198, handle:2, event:UP, 
[Apr  4 15:26:01.778] Event: V1 FSM ld:4198 handle:2 event:RX UP state:UP
[Apr  4 15:26:01.777] Event: notify client(OSPF) IP:10.3.3.2, ld:4198, handle:2, event:UP, 
[Apr  4 15:26:01.777] Event: V1 FSM ld:4198 handle:2 event:RX INIT state:DOWN
[Apr  4 15:26:01.776] Event: V1 FSM ld:4198 handle:2 event:Session create state:ADMIN DOWN
[Apr  4 15:25:59.309] Event: 
 bfd_session_destroyed, proc:CEF, handle:2 act
[Apr  4 15:25:59.309] Event: V1 FSM ld:4198 handle:2 event:Session delete state:UP
[Apr  4 15:25:59.308] Event: 
 bfd_session_destroyed, proc:OSPF, handle:2 act
[Apr  4 15:22:48.912] Event: V1 FSM ld:4198 handle:2 event:RX UP state:UP
[Apr  4 15:22:48.911] Event: notify client(CEF) IP:10.3.3.2, ld:4198, handle:2, event:UP, 
[Apr  4 15:22:48.911] Event: notify client(OSPF) IP:10.3.3.2, ld:4198, handle:2, event:UP, 
[Apr  4 15:22:48.911] Event: notify client(CEF) IP:10.3.3.2, ld:4198, handle:2, event:UP, 
IPv4 Sessions
NeighAddr                              LD/RD         RH/RS     State     Int
[Apr  4 15:22:48.911] Event: V1 FSM ld:4198 handle:2 event:RX INIT state:DOWN
[Apr  4 15:22:48.910] Event: V1 FSM ld:4198 handle:2 event:Session create state:DOWN
[Apr  4 15:22:48.909] 
 bfd_session_created, proc:OSPF, idb:GigabitEthernet3 handle:2 act

Related Information

Cisco IOS BFD Reference

BFD Configuration Guide, Cisco IOS XE 17.x

IETF RFC 5880 for BFD

Revision History

Revision	Publish Date	Comments
1.0	06-Apr-2023	Initial Release

Contributed by Cisco Engineers

Jarrod Best
Cisco TAC Engineer

Troubleshoot Bidirectional Forwarding Detection in Cisco IOS XE

Available Languages

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Bias-Free Language

Contents

Introduction

Prerequisites

Requirements

Components Used

BFD Overview

BFD Modes of Operation

Troubleshoot BFD Problems

BFD Down

BFD Neighbor Flaps

Neighbor Flaps Due to Packet Loss

Neighbor Flaps Due to Parameters Set Too Low

BFD Does Not Fail Over When Strict Mode is Not Configured

Useful Show Commands

Show BFD Neighbor Details

Show BFD Summary

Show BFD Drops

Show BFD Neighbors History

Related Information

Revision History

Contributed by Cisco Engineers

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