forkid (EIP-2124) was designed to permit two Ethereum nodes to quickly and cheaply decide if they are compatible or not, not only at a genesis/networking level, but also from the perspective of the currently passed network updates (i.e. forks).
EIP-2124 only defines how the
forkid is calculated and validated, but does not specify how the
forkid should be exchanged between peers. This EIP specifies the inclusion of the
forkid as a new field in the Ethereum wire protocol (
eth) handshake (releasing a new version,
forkid during the handshake, incompatible nodes can disconnect before expensive block exchanges and validations take place (PoW check, EVM execution, state reconstruction). This further prevents peer slots from being taken up by nodes that are incompatible, but have not yet been detected as such.
From a micro perspective, cutting off incompatible nodes from one another ensures that a node only spends its resources on tasks that are genuinely useful to it. The sooner we can decide the remote peer is useless, the less time and processing we expend in vain.
From a macro perspective, keeping incompatible nodes partitioned from one another ensures that disjoint clusters retain more resources for maintaining their own chain, thus raising the quality of service for all networks globally.
The specification is tiny since most parts are already specified in EIP-2124.
eth/63 is not specified as an EIP, but is maintained here.
forkidgeneration and validation per EIP-2124.
- Advertise a new
ethprotocol capability (version) at
- The old
eth/63protocol should still be kept alive side-by-side, until
eth/64is sufficiently adopted by implementors.
- The old
eth/64to add a trailing
- Old packet:
[protocolVersion, networkId, td, bestHash, genesisHash]
- New packet:
[protocolVersion, networkId, td, bestHash, genesisHash, forkid], where
[forkHash: byte, forkNext: uint64](fields per EIP-2124 ).
- Old packet:
Whenever two peers connect using the
eth/64 protocol, the updated
Status message must be sent as the protocol handshake, and each peer must validate the remote
forkid, disconnecting at a detected incompatibility.
EIP-2124 mentions advertising the
forkid in the discovery protocol too. How does that compare to advertising in the
eth protocol? Why is the redundancy needed?
Advertising and validating the
forkid in the discovery protocol is a more optimal solution, as it can help avoid the cost of setting up the TCP connection and cryptographic RLPx stream, only to be torn down if
eth/64 rejects it.
Compared to the
eth protocol however, discovery is a bit fuzzy. The goal there is to suggest potential peers, not to be fool-proof. Information may be outdated, nodes may have changed or disappeared. Discovery can do a rough filtering, but more precision is still needed afterwards.
forkid validation via the discovery protocol requires ENR implementation (EIP-778) and ENR extension support (EIP-868), which is not mandated by the Ethereum network currently. Lastly, the discovery protocol is just one way to find peers, but systems that cannot use UDP or that rely on other mechanism (e.g. DNS discovery (EIP-1459)) still need a way to filter connections.
forkid implicitly contains the genesis hash checksummed into the
FORK_HASH field. Why doesn’t this proposal remove the
genesisHash field from the
Originally this EIP did remove it as redundant data, since filtering based on the
forkid is a superset of filtering based on genesis hash. The reason for backing out of that decision was that the genesis hash may be useful for other things too, not just connection filtering (network crawlers use it currently to split nodes across networks).
forkid will hopefully take over all the roles of the genesis hash currently in use, there’s no reason to be overly aggressive in deduplicating data. It’s fine to keep both side-by-side for now, and remove in a future version when 3rd party infrastructures switch over.
This EIP extends the
eth protocol handshake in a backwards incompatible way and requires rolling out a new version,
devp2p supports running multiple versions of the same wire protocol side-by-side, so rolling out
eth/64 does not require client coordination, since non-updated clients can keep using
This EIP does not change the consensus engine, thus does not require a hard fork.
For calculating and validating fork IDs, see test cases in EIP-2124.
Testing proper advertising and validation at the networking level will require a hive test.
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