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With alternate IP configured, MLAG ports may be disabled momentarily when other MLAG peer comes Up after reboot

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TitleWith alternate IP configured, MLAG ports may be disabled momentarily when other MLAG peer comes Up after reboot
Symptoms
  • If rebooting one node in an Mlag pair it is possible that the ports on the active node can be disabled momentarily.
  • This only happens if Mlag Alternate IP is configured.
  • When Mlag Alternate IP is configured, it will establish an health-check connection with the peer and will exchange health-check messages periodically.
  • In cases where alternate IP is reachable but the ISC link is down (during booutp), the MLAG Peer which has lowest IP( i.e. lowest alternate IP) will disable all its MLAG ports to avoid any loop because of ISC down.  
  • Once ISC port comes UP, it will enable all the MLAG ports again. 
  • Therefore there is a 50% chance of temporary loss of connectivity during reboot of one node, depending which node is reset.
Environment
  • EXOS
  • Mlag
  • Alternate IP
  • Firmware Version 15.5.1 and higher
 
Cause
When the rebooted node comes UP, the alternate IP is reachable before the MLAG ports come up.  As soon the MLAG peer is reachable through alternate IP, it is expected for an MLAG node that possess lower IP(alternate - Mgmt) to disable its MLAG ports until ISC comes UP.
Resolution
The fix for this issue has been released in 

EXOS 21.1.5 
EXOS 16.2.4 

Awaiting GA release of the fix in: 

EXOS 22.5.1 


Workaround

Remove Alternate IP configuration 
Additional notes

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