Using the Standard Bridge

... About 3 min

Certain interactions, like transferring SYS and ERC-20 tokens between the two networks, are common enough that we've built the "Standard Bridge" to make moving these assets between L1 and L2 as easy as possible.

The standard bridge functionality provides a method for an ERC-20 token to be deposited and locked on L1 in exchange of the same amount of an equivalent token on L2. This process is known as "bridging a token", e.g. depositing 100 USDC on L1 in exchange for 100 USDC on L2 and also the reverse - withdrawing 100 USDC on L2 in exchange for the same amount on L1. In addition to bridging tokens the standard bridge is also used for SYS.

The Standard Bridge is composed of two main contracts the L1StandardBridge (opens new window) (for Layer 1) and the L2StandardBridge (opens new window) (for Layer 2).

Here we'll go over the basics of using this bridge to move ERC-20 assets between Layer 1 and Layer 2.

# Deposits


We're working hard to get more smart contract wallet software deployed and tested on Rollux. However, as a safety measure, we currently block smart contract wallets from calling the depositETH and depositERC20 functions. If you want to deposit using a smart contract wallet and you know what you're doing, you can use the depositETHTo and depositERC20To functions instead.

# Depositing ERC20s

ERC-20 deposits into L2 can be triggered via the depositERC20 and depositERC20To functions on the L1StandardBridge (opens new window). You must approve the Standard Token Bridge to use the amount of tokens that you want to deposit or the deposit will fail.

Use the standard bridge contract only with standard bridge tokens

The standard bridge can only be used with tokens that have a properly configured ERC-20 version on Rollux. If you send any other type of token to the standard bridge directly (not using the user interface or the API), it gets stuck there and you lose that value.

Note that if you use the Rollux bridge UI (opens new window), or the SDK it automatically chooses the correct bridge contract, so this problem does not happen.

How to check for sure if a token can use the standard bridge:

  1. The token is present in the Rollux token list (opens new window), and has

"Ask" the L2 token contract by calling it. ERC-20 tokens can use the standard bridge if they:

  • Have an l2Bridge method
  • That method returns 0x4200...0010.

The Rollux explorer (opens new window) can be used to view a verified token's methods and place the call.

Note that you cannot query the L1 token contract the same way. L2 contracts know the identity of their L1 counterpart, but L1 contracts only need to implement the standard ERC-20 methods.

# Depositing SYS

SYS deposits into L2 can be triggered via the depositETH and depositETHTo functions on the L1StandardBridge (opens new window). SYS deposits can alternatively be triggered by sending SYS directly to the L1StandardBridge. Once your deposit is detected and finalized on Rollux, your account will be funded with the corresponding amount of SYS on L2.

# Withdrawals

# Withdrawing ERC-20s

ERC-20 withdrawals can be triggered via the withdraw or withdrawTo functions on the L2StandardBridge (opens new window). If you'd like to see this contracts in action, you should check out the L1 ⇔ L2 deposit-and-withdraw example (opens new window).

# Withdrawing SYS

Unlike on L1, we do not have a separate function on L2 for withdrawing SYS. Instead, you can use the withdraw or withdrawTo functions on the L2StandardBridge (opens new window) and use the address 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000 as the L2 token address.

# Adding an ERC-20 token to the Standard Bridge


To add your token to the standard bridge, see the guide Adding an ERC-20 token to the Standard Bridge (opens new window).

# The Rollux token list

The Standard bridge allows a one-to-many mapping between L1 and L2 tokens, meaning that there can be many Rollux implementations of an L1 token. However there is always a one-to-one mapping between L1 and L2 tokens in the Rollux token list (opens new window). The token list is used as the source of truth for the Rollux Portal (opens new window) which is the main portal for moving assets between Layer 1 and Layer 2.

If you want to have your token added to the token list, you must make a pull request against the token list repository (opens new window). You'll need the addresses for both the L1 and L2 tokens, as well as a logo for the token.