Why is it not possible to configure L2TPv3 or Transparent mode in a cOS Core high availability cluster?
The reason for this is because there is no state synchronization for Transparent Mode and no loop avoidance.
Running transparent mode on an HA cluster would result in the same situation as when two switches are connected to each other over multiple links. One single packet entering the system could, in the worst case, cause a never-ending packet loop between the two cluster nodes. Besides keeping the HA cluster fully busy, this will also mean that multiple copies of the packet will be generated on all involved interfaces, meaning that the HA cluster would more or less become a packet generator (if it was allowed).
And since L2TPv3 relies on transparent routing to bridge the networks using layer 2, it will also not work in high availability clusters.
Is it a bug or per design?
It is not a bug, it is how the system was designed based on the use-cases that were most sought after at the time of implementation.
Will it be changed in the future?
At this time (2023) there are no plans to add support for transparent mode in HA clusters. There exists an RFE (request for enhancement) with ID COP-17647 but it would be a fairly large project that is not planned or included in any roadmaps at this time. Clavister is, however, always interested in getting feedback from customers about features they would like to see implemented. The more customers who are interested in a particular feature, the higher the chance that it will be implemented. If you are interested in this particular functionality you can contact Clavister support and indicate this with a reference to the development ID (COP-17647), including a description of use-case for the feature.
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