Link Detection Debounce Timer
The link debounce timer avoids frequent updates (churn) to higher layer protocols during flapping of an interface. The initial link state is UP. The link goes DOWN. If the Link comes UP and goes DOWN, The link DOWN AND link UP timer is started and being restarted on each flap (link comes up and goes down again). For each link DOWN, link down timer will start and it restarts on flap within the link debounce interval. For each link UP, link up timer will start and it restarts on flap within the link debounce interval
Note: Keep the following in mind when using the Link detection debounce timer:
• Link debounce timer is supported only for physical L2 and L3 interfaces.
• When debounce timer is configured we won't be able to configure the link-debounce-timer config and viceversa.
• The link debounce flap-count refers to the number of flaps OcNOS receives while the debounce timer is running:
• The flap-count is only updated if the timer is still running and OcNOS receives a link status event for the interface.
• The flap-count is reset at the subsequent start of the link debounce timer.
• Protocol-specific timers such as BFD which depend on the link status should be configured to minimum of 1.5 times the value of the link-debounce time. Otherwise it could affect the protocol states if the link debounce timer is still running.
• Protocols such as PO, OSPF, BFD, ISIS, BGP which depends on the link status, in this case we should ensure on both the connected interfaces we need to configure the link-debounce timer.
Topology
Link detection debounce timer topology
Configuration
RTR1
#configure terminal | Enter configure mode. |
(config)#interface xe1 | Enter interface mode |
(config-if)#link-debounce-time 4000 5000 | Configure link-debounce-time where link-up timer is 4000 ms and link-down timer is 5000 ms |
(config-if)#commit | Commit the candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode |
RTR2
#configure terminal | Enter configure mode. |
(config)#interface xe1 | Enter interface mode |
(config-if)#link-debounce-time 4000 5000 | Configure link-debounce-time where link-up timer is 4000 ms and link-down timer is 5000 ms |
(config-if)#commit | Commit the candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode |
Validation
#show interface xe1 | i Debounce Link Debounce timer: enable
Linkup Debounce time 4000 ms Linkdown Debounce time 5000 ms
Linkup Debounce status : idle
Linkdown Debounce status : idle
RTR1 and RTR2 outputs after interface flap:
#show interface xe1 | i debounce Link Debounce timer: enable
Linkup Debounce time 4000 ms Linkdown Debounce time 5000 ms
Flap Count: 1
Last Debounce Flap :
Linkup Debounce status : idle
Linkdown Debounce status : idle
#show interface xe1 | i debounce
Link Debounce timer: enable
Linkup Debounce time 4000 ms Linkdown Debounce time 5000 ms
Flap Count: 1
Last Debounce Flap : Linkup Debounce status : idle
Linkdown Debounce status : idle
Log Messages
The following is a configuration example to log link debounce timer activity
:
#configure terminal | Enter Configure mode |
(config)#logging level nsm 7 | Enable operational log to display debounce start and end. |
Example Log Messages
2019 Feb 28 02:50:40.761 : OcNOS : NSM : INFO : Start UP->DOWN Link Debounce Timer on interface xe1
2019 Feb 28 02:50:40.761 : OcNOS : NSM : NOTIF : [DEBOUNCE_EVENT_4]: Interface xe1 changed state from up to down
2019 Feb 28 02:50:43.543 : OcNOS : NSM : INFO : Start DOWN->UP Link Debounce Timer on interface xe1
2019 Feb 28 02:50:43.543 : OcNOS : NSM : INFO : Interface xe1 Flapped, prev_state DOWN new_state UP,flap count 1
2019 Feb 28 02:50:43.543 : OcNOS : NSM : NOTIF : [DEBOUNCE_EVENT_4]: Interface xe1 changed state from down to up
2019 Feb 28 02:50:45.761 : OcNOS : NSM : INFO : Link Debounce Timer Expired on interface xe1 (initiated transition up->down), prev_state UP, new_state UP
2019 Feb 28 02:50:47.544 : OcNOS : NSM : INFO : Link Debounce Timer Expired on interface xe1 (initiated transition down->up), prev_state UP, new_state UP