Leios scaling threatens Cardano stability unless fast path passes

Cardano could give governance a faster way to disable its proposed Leios scaling system during a serious network problem while keeping restarts under normal approval rules.

A Nov. 6 proposal from Kevin Hammond would relax notice and frequency limits for emergency deactivation, without removing the votes or enactment steps needed to change the protocol.

Hammond set out the approach in the Cardano Amendment Proposal 12 (CAP-12) technical discussion, calling it a proposed Technical Steering Committee position ahead of a Nov. 18 review. CAP-12 is a proposed constitutional amendment setting limits for Dijkstra-era protocol parameters.

CAP-12 version 5, which remained open on Nov. 8, prohibits zero-valued Leios parameters, and Hammond’s network-wide shutdown route would use one.

Cardano keeps ordinary restart

The proposed switch is intended to disable Leios’s additional transaction-processing path while preserving ordinary block production. It would set maxEndorserBlockTxsSize, the limit on transaction payload endorsed by a supplementary block, to zero.

These endorser blocks reference additional transactions, which enter the chain after certification and inclusion of the certificate in a later ranking block.

For a Severity 1 or Severity 2 network issue, Hammond’s fast path would waive the PARAM-04a notice requirement and permit the transition to zero in any epoch.

Switching Leios back on would follow the normal process and remain subject to the network-group frequency limit.

Hammond said ratification and enactment would still take at least one epoch boundary, describing a boundary the action must pass.

Notice and frequency exceptions would stop at deactivation.

Proposed, not enacted. CAP-12 v5 still forbids zero; behavioral confirmation and switching/conformance tests are prerequisites, with completion unconfirmed in reviewed records.

Sources and evidence

Sources

1. Kevin Hammond’s proposed TSC position, November 6
2. CAP-12 version 5, current constitutional proposal

Supporting facts

• CAP-12 remained open in the November 8 capture; its current version 5 analysis prohibits setting any Leios parameter to zero, and MEBTS-09 explicitly forbids zero for maxEndorserBlockTxsSize. [2]
• Hammond proposed maxEndorserBlockTxsSize = 0 as the official network-wide Linear Leios deactivation path, conditional on written team confirmation and tests. [1]
• Hammond’s proposed emergency fast path would waive PARAM-04a notice only for switch-off in response to a Severity 1 or 2 network issue; switch-on would follow the normal process. [1]
• Hammond said that even with the proposed notice waiver, ratification and enactment would still take at least one epoch boundary. [1]
• Hammond proposed allowing the transition to zero in any epoch, while keeping switch-on subject to the network-group frequency limit. [1]
• CAP-12’s current analysis says Leios parameter changes require DReps, the Constitutional Committee and an SPO vote; the proposed shutdown route would remain a governance-controlled parameter change. [2] [1]
• Hammond made Preview and Preprod switch-off and switch-back-on exercises, measurements against the Praos block-production baseline, and zero-setting conformance tests across all node implementations conditions of his proposal. [1]

Method

Qualitative route diagram drawn from CAP-12 and Hammond’s November 6 proposed TSC position. No elapsed-time scale, computed quantities or adopted network behavior is implied.

Scope

Proposed, not enacted. CAP-12 v5 still forbids zero; behavioral confirmation and switching/conformance tests are prerequisites, with completion unconfirmed in reviewed records.

Infographic by CryptoSlate

CAP-12’s analysis says Leios parameter changes require delegated representatives, the Constitutional Committee and a stake-pool-operator vote. Hammond separately distinguished that governance-controlled protocol switch from an operational switch based on ad-hoc operator participation.

Hammond made the protocol route conditional on written confirmation from the Linear Leios team about what zero does. No endorser blocks should be announced, no votes cast or diffused, and no certificates included in ranking blocks.

Node behavior should be equivalent to Praos, Cardano’s existing block-production system.

He also required switch-off and switch-back-on exercises on the Preview and Preprod test networks, with block production measured against the Praos baseline, plus conformance tests for the zero setting across all node implementations.

Constitutional permission to set a value would still need a matching implementation: clients must interpret zero consistently, and switching back on must work as intended.

Meanwhile, version 5’s MEBTS-09 rule expressly says the parameter must not be zero. Intersect’s Nov. 6 update confirms that the off switch was removed from the constitutional text, with deactivation left to the hard-fork plan and another draft expected.

Adopting Hammond’s route would require reconciling that ban with the proposed exception.

Testing and the constitutional timetable

The Nov. 3 working-group minutes say the test network entered the Dijkstra era on Nov. 2 using node 11.2, without full Leios implementation.

Intersect said on Nov. 6 that DijkstraNet supported BLS key registration but not full Linear Leios. Full Leios was available for early integration testing on Musashi, while the combined node 11.3 release candidate was estimated to be at least two to three weeks away.

The Nov. 3 consensus update reports endorser-block forging, certificate checks, and vote relaying. Essential Cardano’s Nov. 6 summary describes those main-branch changes as development work rather than a mainnet release.

The working-group minutes record an aim to submit the constitution and guardrails by Nov. 25.

Hammond also said on Nov. 6 that the Parameter Committee had not yet seen the pending numerical values and would need time to review them.