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Cisco Bug: CSCvt36353 - MAC Cache displays erroneous ages for MACs

Last Modified

Sep 02, 2020

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

7.1.2.BASE

Description (partial)

Symptom:
This is a cosmetic issue where MAC Cache may intermittently display erroneous ages for MACs; for example, MACs may be shown with an age approximately 2.12 hours in the past.

RP/0/RSP1/CPU0:R1-PE1#sh clock
17:03:31.589 UTC Tue Mar 3 2020
RP/0/RSP1/CPU0:R1-PE1#show l2vpn forwarding bridge-domain mac-address location 0/1/CPU0
 To Resynchronize MAC table from the Network Processors, use the command...
    l2vpn resynchronize forwarding mac-address-table location <r/s/i>
 
Mac Address    Type    Learned from/Filtered on    LC learned Resync Age/Last Change Mapped to      
-------------- ------- --------------------------- ---------- ---------------------- -------------- 
0022.9400.0001 dynamic Hu0/1/0/15.10000            N/A        03 Mar 17:02:04        N/A            
0022.9400.0002 dynamic Hu0/1/0/15.10000            N/A        03 Mar 17:02:04        N/A            
0022.9400.0003 dynamic Hu0/1/0/15.10000            N/A        03 Mar 17:02:04        N/A            
 
          
RP/0/RSP1/CPU0:R1-PE1#sh clock
17:03:47.239 UTC Tue Mar 3 2020
RP/0/RSP1/CPU0:R1-PE1#show l2vpn forwarding bridge-domain mac-address location 0/1/CPU0
 To Resynchronize MAC table from the Network Processors, use the command...
    l2vpn resynchronize forwarding mac-address-table location <r/s/i>
 
Mac Address    Type    Learned from/Filtered on    LC learned Resync Age/Last Change Mapped to      
-------------- ------- --------------------------- ---------- ---------------------- -------------- 
0022.9400.0001 dynamic Hu0/1/0/15.10000            N/A        03 Mar 14:56:22        N/A            
0022.9400.0002 dynamic Hu0/1/0/15.10000            N/A        03 Mar 14:56:22        N/A            
0022.9400.0003 dynamic Hu0/1/0/15.10000            N/A        03 Mar 14:56:22        N/A            
0022.9400.0004 dynamic Hu0/1/0/15.10000            N/A        03 Mar 14:56:22        N/A

Conditions:
The issue is observed on Lightspeed cards.  When the MAC Cache CLI is invoked, the mac age timer is read and then the mac addresses are read from the data plane; the time read and the timestamp stored with mac addresses are compared to give an approximate age for mac addresses which are displayed in the CLI.  If a mac's timestamp is updated after the mac age timer is read, the mac may appear to have an age of approximately 2.12 hours in the past.  This scenario may more readily be observed at large mac scale with mac addresses frequently having their timestamp updated (such as with frequent mac moves).
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