EIP-7934: RLP Execution Block Size Limit

Introduce a protocol-level cap on the maximum RLP-encoded block size to 10 MiB, including a 512 KiB margin for beacon block size.

Abstract

This proposal introduces a protocol-level cap on the maximum RLP-encoded execution block size to 10 megabytes (MiB), which includes a margin of 512 KiB to account for beacon block sizes.

Motivation

Currently, Ethereum does not enforce a strict upper limit on the encoded size of blocks. This lack of constraint can result in:

1. Network Instability: Extremely large blocks slow down propagation and increase the risk of temporary forks and reorgs.
2. DoS Risks: Malicious actors could generate exceptionally large blocks to disrupt network performance.

Additionally, blocks exceeding 10 MiB are not propagated by the consensus layer’s (CL) gossip protocol, potentially causing network fragmentation or denial-of-service (DoS) conditions.

By imposing a protocol-level limit on the RLP-encoded block size, Ethereum can ensure enhanced resilience against targeted attacks on block validation times. Adding an additional margin of 512 KiB explicitly accommodates beacon block sizes, ensuring compatibility across network components.

Specification

Block Size Cap

• Introduce constants:
  • MAX_BLOCK_SIZE set to 10 MiB (10,485,760 bytes)
  • MARGIN set to 512 KiB (524,288 bytes)
  • MAX_RLP_BLOCK_SIZE calculated as MAX_BLOCK_SIZE - MARGIN
• Any RLP-encoded block exceeding MAX_RLP_BLOCK_SIZE must be considered invalid.

Thus add the following check to the Ethereum protocol:

MAX_BLOCK_SIZE = 10_485_760  # 10 MiB
SAFETY_MARGIN = 524_288  # 512 KiB
MAX_RLP_BLOCK_SIZE = GOSSIP_UPPER_LIMIT - SAFETY_MARGIN

# if true, the block is invalid and should be rejected/not get built
def exceed_max_rlp_block_size(block: Block) -> bool:
    return len(rlp.encode(block)) > MAX_RLP_BLOCK_SIZE

Changes to Protocol Behavior

1. Block Creation: Validators must ensure the total RLP-encoded size of any produced block does not exceed MAX_RLP_BLOCK_SIZE.
2. Block Validation: Nodes must reject blocks whose RLP-encoded size exceeds MAX_RLP_BLOCK_SIZE.

Protocol Adjustment

• All Ethereum client implementations must integrate this size check as part of block validation and propagation.
• This limit applies independently of gas-related metrics.

Rationale

Why 10 MiB?

A cap of 10 MiB aligns with the gossip protocol constraint in Ethereum’s consensus layer (CL). An additional 512 KiB margin explicitly accounts for beacon block sizes, ensuring compatibility and consistent block propagation across the network. Blocks significantly larger than 10 MiB will not be broadcast by the CL, potentially leading to network fragmentation or denial-of-service scenarios.

Backwards Compatibility

This change is not backward-compatible with any blocks larger than the newly specified size limit. Validators and miners will need to ensure their block construction logic strictly respects this limit.

Security Considerations

Restricting maximum block size provides inherent protection against deliberate oversized-block attacks.

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Giulio Rebuffo (@Giulio2002), Ben Adams (@benaadams), Storm Slivkoff (@sslivkoff), "EIP-7934: RLP Execution Block Size Limit [DRAFT]," Ethereum Improvement Proposals, no. 7934, April 2025. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-7934.