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VPC Consistency Check and failover Scenarios

VPC Consistency Check and failover Scenarios

Posted on Jan 24, 2020 (0)

VPC Consistency Check and failover Scenarios

Cisco Fabric Services (CFS) Protocol:

Cisco Fabric Services CFS is the reliable protocol performs the following functions:

  • Configure validation and comparison (consistency check)
  • Synchronization of MAC addresses for vPC member ports
  • vPC member port status advertisement
  • Spanning Tree Protocol management
  • Synchronization of HSRP and IGMP snooping

Cisco fabric Service is enabled by default as soon as vPC feature is turned on. CFS message are encapsulated in Ethernet frame and is tagged with COS 4 for reliable communication.

You can check the CFS for vPC

7K1# sh cfs application
----------------------------------------------
Application     Enabled       Scope
----------------------------------------------
arp                   Yes          Physical-eth
pim                  Yes          Physical-eth
stp                   Yes          Physical-eth
vpc                  Yes          Physical-eth
igmp                Yes          Physical-eth
l2fm                 Yes          Physical-eth

vPC Configuration consistency check

As soon as vPC feature is enabled, CFS starts working and after configuration is done then via CFS protocol it check and validates the configuration at both Peer device. Based on configuration Validation and comparison CFS divides the configuration and its error in to two types:

There are two types of consistency checks:

  • Type 1 - Puts peer device or interface into a suspended state to prevent invalid packet forwarding behaviour. With vPC Graceful Consistency check, suspension occurs only on the secondary peer device.
  • Type 2 - Peer device or Interface still forward traffic. However they are subject to undesired packet forwarding behaviour.

Type 1 and Type 2 consistency check apply both for global configuration and for vPC interface configuration.

Type-1 Consistency Check:

Once CFS starts running on both peer-devices, the CFS protocols provide a copy of the configuration on the local vPC peer device to remote vPC device. The per-interface parameters must be consistent per interface, and the global parameters must be consistent globally.

When Type 1 inconsistency is detected then following action is taken:

  • For global configuration type 1 inconsistency check, all vPC member ports are set to down state.
  • For vPC interface configuration type 1 inconsistency check, the misconfigured vPC is set to down state.

Use the following command to check and display the global configuration and vPC

Show vpc consistency-parameters global

Below lists global configuration parameters that are taken into account for type-1 consistency check.

Below lists the per vPC interface parameters that are taken into account for type-1 consistency check.

Use the following command to check and display the interface configuration and vPC

Show vpc consistency-parameters interface port-channel < Id >

Type-2 Consistency Check

When the Type-2 inconsistency check is detected, moderate action or no action is taken. 

For global configuration type 2 inconsistency check, all vPC member ports remain in up state and vPC systems trigger to protective actions.


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