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How to set up an AEP fee router

Quick start​

Canonical contracts​

NetworkContractAddressConfigured for
EthereumParent2ChildRouter0x40Cd7D713D7ae463f95cE5d342Ea6E7F5cF7C999ETH, ERC-20
Arbitrum NovaChild2ParentRouter0x36D0170D92F66e8949eB276C3AC4FEA64f83704dETH
BaseChild2ParentRouter0x1015c1ae166c4c39d18a1151b7029bac1530c9aaETH

The AEP fee router contract system​

This section describes the different fee distribution and router contracts that are available. You can find their source code here.

RewardDistributor​

The AEP fee router system relies on configuring an escrow contract as the intended reward address for protocol fee components. This intermediary contract is known as the RewardDistributor.

The RewardDistributor is configured to separate the AEP portion of the fees from fees intended for the chain owner. The RewardDistributor can be permissionlessly called to perform a withdrawal which simultaneously transfers 90% of accrued fees to the chain’s fee collector and 10% of accrued fees to a routing contract on the parent chain. From here, the chain owner has complete control over their earned fees, and the routing contracts can direct AEP fees to a collecting address for the Arbitrum DAO.

ChildToParentRouter​

AEP fees from the RewardDistributor must first be sent to Ethereum before they can be deposited to the DAO-controlled address on Arbitrum One. To facilitate this transfer to Ethereum, AEP fees are sent through a series of contracts known as ChildToParentRouters.

The ChildToParentRouter is configured to withdraw a single token (immutable and specified at deployment) from the child chain to a specific target address on the parent chain: either another ChildToParentRouter or the ParentToChildRouter on Ethereum.

ParentToChildRouter​

All AEP fees from the network of Orbit chains will arrive at the ParentToChildRouter on Ethereum. This contract can send ETH and arbitrary ERC-20 tokens to a DAO-controlled address on Arbitrum One.

Deploying your AEP fee router contracts​

An Orbit chain is responsible for deploying all ChildToParentRouters necessary for their AEP funds to arrive at the ParentToChildRouter on Ethereum.

This includes:

  • Deploying a ChildToParentRouter on their Orbit chain configured for their gas token and configured to send funds to either:
    • The ParentToChildRouter on Ethereum (assuming the network is a Layer-2)
    • Another ChildToParentRouter configured to the same gas token and configured to send funds to a successive parent chain (this is the case for a Layer-3 network or higher)
  • Deploying a RewardDistributor contract configured to forward 10% of fees to the ChildToParentRouter and 90% to the chain owner’s preferred reward-receiving address.

In the event that a ChildToParentRouter does not connect to the ParentToChildRouter on Ethereum, an Orbit chain must deploy successive ChildToParentRouter contracts until a connection to ParentToChildRouter is established.

And optionally, an Orbit chain can decide to deduct assertion costs by following the instructions in the Deducting Assertion Costs section:

Deployment scripts​

The Orbit SDK provides a configurable script that allows a chain operator to deploy quickly and set up the AEP fee router contracts.

Note for L3 chains with custom gas tokens

The standard script deploys and sets up the AEP fee router contracts to route funds to the parent chain. L2 chains are expectd to route funds to the ParentToChildRouter contract living on Ethereum. L3 chains (or further layers) might need to specify a different target address on the parent chain depending on the gas token of the chain. If the chain uses ETH as the gas token, and a ChildToParentRouter contract is deployed in the parent chain, they can route their funds to that contract. If the chain uses a different gas token, please contact the Arbitrum Foundation to confirm the target address to withdraw the AEP fees to.

The script performs the following operations:

  1. Obtain the rollup and inbox contract of the chain. These are needed to execute the next steps.
  2. Obtain the current fee collectors of the chain: Orbit base fee collector, Orbit surplus fee collector, and Parent chain surplus fee collector.
  3. Deploy the ChildToParentRouter contract, configured to send the amounts received to the appropriate target address on the parent chain.
  4. Deploy a RewardDistributor contract for each different fee collector account, configured to distribute 90% of the amounts received to the current fee collector, and 10% to the ChildToParentRouter contract deployed in the previous step.
  5. Set each of the fee collectors to the RewardDistributor contracts
info

Note that if the same address collects all three fee types, only one RewardDistributor contract will be deployed, which will collect all those fees.

To configure the script, you need to specify the following environment variables:

  • ROLLUP_ADDRESS: address of the rollup contract
  • CHAIN_OWNER_PRIVATE_KEY: private key of the account with executor privileges in the UpgradeExecutor admin contract for the chain
  • ORBIT_CHAIN_ID: chain id of the Orbit chain
  • ORBIT_CHAIN_RPC: RPC of the Orbit chain
  • PARENT_CHAIN_ID: chain id of the parent chain, which shouldn't be an Arbitrum chain
  • PARENT_CHAIN_TARGET_ADDRESS: address on the parent chain where 10% of the revenue will be sent to. You can find the potential target addresses in the canonical contracts section of this document. If the parent chain is not on that list, or if your chain uses a gas token different than the one the router is configured for, contact the Arbitrum Foundation to obtain a specific target address for your chain.

Finally, follow these steps to execute the script (from the examples/setup-aep-fee-router folder):

  1. Install dependencies
yarn install
  1. Create .env file and add the env vars
cp .env.example .env
  1. Run the script
yarn dev