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BFD Flapping

Publication Date:  2017-08-01 Views:  206 Downloads:  0
Issue Description

For Expansion purpose , we migrate configuration from S5700HI to S6720EI series switch . after migrate BDF session start to flapping. 

Alarm Information

The log on the switch includes BFD FOR ISIS flapping records and many BFD packets dropped by CPCAR.
BFD and ISIS flapping records:


Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01BFD/4/STACHG_TODWN(l)[421199]:BFD session changed to Down. (SlotNumber=0, Discriminator=9467, Diagnostic=DetectDown, Applications=ISISL2, ProcessPST=False, BindInterfaceName=Vlanif32, InterfacePhysicalState=Up, InterfaceProtocolState=Up)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01BFD/4/STACHG_TODWN(l)[421205]:BFD session changed to Down. (SlotNumber=0, Discriminator=9416, Diagnostic=DetectDown, Applications=ISISL2, ProcessPST=False, BindInterfaceName=Vlanif31, InterfacePhysicalState=Up, InterfaceProtocolState=Up)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01BFD/4/STACHG_TODWN(l)[421214]:BFD session changed to Down. (SlotNumber=0, Discriminator=9446, Diagnostic=DetectDown, Applications=ISISL2, ProcessPST=False, BindInterfaceName=Vlanif26, InterfacePhysicalState=Up, InterfaceProtocolState=Up)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01BFD/4/STACHG_TODWN(l)[421222]:BFD session changed to Down. (SlotNumber=0, Discriminator=9468, Diagnostic=DetectDown, Applications=ISISL2, ProcessPST=False, BindInterfaceName=Vlanif33, InterfacePhysicalState=Up, InterfaceProtocolState=Up)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01BFD/4/STACHG_TODWN(l)[421227]:BFD session changed to Down. (SlotNumber=0, Discriminator=9469, Diagnostic=DetectDown, Applications=ISISL2, ProcessPST=False, BindInterfaceName=Vlanif34, InterfacePhysicalState=Up, InterfaceProtocolState=Up)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01ISIS/4/ADJ_CHANGE_LEVEL(l)[421193]:The neighbor of ISIS was changed. (IsisProcessId=1, Neighbor=0101.5000.2078, InterfaceName=Vlanif25, CurrentState=up, ChangeType=NEW_L2_ADJ, Level=Level-2)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01ISIS/4/ADJ_CHANGE_LEVEL(l)[421204]:The neighbor of ISIS was changed. (IsisProcessId=1, Neighbor=0101.5000.2096, InterfaceName=Vlanif32, CurrentState=down, ChangeType=L2_BFD_DOWN, Level=Level-2)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01ISIS/4/ADJ_CHANGE_LEVEL(l)[421206]:The neighbor of ISIS was changed. (IsisProcessId=1, Neighbor=0101.5000.2097, InterfaceName=Vlanif31, CurrentState=down, ChangeType=L2_BFD_DOWN, Level=Level-2)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01ISIS/4/ADJ_CHANGE_LEVEL(l)[421207]:The neighbor of ISIS was changed. (IsisProcessId=1, Neighbor=0101.5000.2096, InterfaceName=Vlanif32, CurrentState=up, ChangeType=NEW_L2_ADJ, Level=Level-2)
Jul 31 2017 12:01:30+05:30 SMB-BX1 %%01ISIS/4/ADJ_CHANGE_LEVEL(l)[421209]:The neighbor of ISIS was changed. (IsisProcessId=1, Neighbor=0101.5000.2097, InterfaceName=Vlanif31, CurrentState=up, ChangeType=NEW_L2_ADJ, Level=Level-2)

Handling Process

By default, the S6720EI allows about 100 BFD packets to pass per second.

On the switch, 13 BFD sessions have been configured and the BFD session interval is 100 ms.

That is, 130 BFD packets are generated every second. The CPCAR does not allow all BFD packets to pass.

BFD session interval is 100 ms:

 

isis 1
 is-level level-2
 timer lsp-generation 1 1 120 level-2
 flash-flood level-2
 bfd all-interfaces enable
 bfd all-interfaces min-tx-interval 100 min-rx-interval 100
 network-entity 10.0101.5000.2076.00
 timer spf 1 20 100

 

BFD packets on the switch are dropped by CPCAR:

After the CPCAR on the live network is modified, the switch can handle more BFD packets. This avoids frequent BFD flapping.

However, it is not recommended to configure more than 8 BFD sessions with interval 100 ms. The recommended BFD session interval is 1s.
Modified CPU-DEFEND configuration:


 cpu-defend policy bfd

 car packet-type bfd cir 128 cbs 24064

 cpu-defend-policy bfd global

 

 




 

 

 

Root Cause

Too many BFD sessions are configured on the S6720EI. When BFD packets are dropped by CPCAR, BFD flapping occurs, causing ISIS flapping.  services got affected.

END