VSF split and MAD operation

The following sequence explains a MAD scheme for a simple 2-member, VSF virtual chassis split scenario.

  1. When the VSF link goes down and the VSF virtual chassis splits:
    • The Commander member ( Fragment-A for this example) would continue to stay active.
    • The Standby member (Fragment B) would failover and become another commander.
  2. Fragment-B sends an SNMP request to the downstream device seeking port status information of all non-local ports of the LACP Trunk. Non-local ports on Fragment-B refers to ports that are part of Fragment-A’s member.

    • The downstream device responds to the SNMP request with the appropriate port status information.
    • If Fragment-A receives an unsolicited response to the SNMP request, it is ignored. This is because Fragment A has the pre-split Commander as part of its fragment and therefore will remain active.
  3. Fragment-B sends 9 more SNMP queries downstream. If no response is received, the frontplane ports are shut down and turned inactive.

  4. Alternatively, if Fragment-B receives an SNMP response:
    • If Fragment A links are UP, the frontplane ports will be shut down.
    • If Fragment-A links are DOWN, Fragment-B would stay UP.
  5. Consider that Fragment-A is actually DOWN which has caused the split:
    • Request made to Fragment-B will be received by the downstream device and response will return to Fragment-B.

    • The downstream links to Fragment-A are DOWN therefore Fragment-B will remain UP.

    • Alternately, if Fragment-B is DOWN and caused the split then Fragment-A will neither send a request or act on an unsolicited response and will remain UP.