CCIP Best Practices

Before you deploy your cross-chain dApps to mainnet, make sure that your dApps follow the best practices in this document. You are responsible for thoroughly reviewing your code and applying best practices to ensure that your cross-chain dApps are secure and reliable. If you have a unique use case for CCIP that might involve additional cross-chain risk, contact the Chainlink Labs Team before deploying your application to mainnet.

Verify destination chain

Before calling the router's ccipSend function, ensure that your code allows users to send CCIP messages to trusted destination chains.

Verify source chain

When implementing the ccipReceive method in a contract residing on the destination chain, ensure to verify the source chain of the incoming CCIP message. This verification ensures that CCIP messages can only be received from trusted source chains.

Verify sender

When implementing the ccipReceive method in a contract residing on the destination chain, it's important to validate the sender of the incoming CCIP message. This check ensures that CCIP messages are received only from trusted sender addresses.

Note: Depending on your use case, this verification might not always be necessary.

Verify router addresses

When you implement the ccipReceive method in the contract residing on the destination chain, validate that the msg.sender is the correct router address. This verification ensures that only the router contract can call the ccipReceive function on the receiver contract and is for developers that want to restrict which accounts are allowed to call ccipReceive.

Setting gasLimit

The gasLimit specifies the maximum amount of gas CCIP can consume to execute ccipReceive() on the contract located on the destination blockchain. It is the main factor in determining the fee to send a message. Unspent gas is not refunded.

To transfer tokens directly to an EOA as a receiver on the destination blockchain, the gasLimit should be set to 0 since there is no ccipReceive() implementation to call.

To estimate the accurate gas limit for your destination contract, consider the following options:

• Leveraging Ethereum client RPC by applying eth_estimateGas on receiver.ccipReceive(). You can find more information on the Ethereum API Documentation and Alchemy documentation.
• Conducting Foundry gas tests.
• Using Hardhat plugin for gas tests.
• Using a blockchain explorer to look up the gas consumption of a particular internal transaction.

Using extraArgs

The purpose of extraArgs is to allow compatibility with future CCIP upgrades. To get this benefit, make sure that extraArgs is mutable in production deployments. This allows you to build it off-chain and pass it in a call to a function or store it in a variable that you can update on-demand.

If extraArgs are left empty, a default of 200000 gasLimit will be set with no strict sequencing.

Sequencing

CCIP always processes messages sent from a specific sender to a specific destination blockchain in the order they were sent. If you set strict: true in the extraArgs part of the message, and if the ccipReceive fails (reverts), it will prevent any following messages from the same sender from being processed until the current message is successfully executed.

You should be very careful when using this feature to avoid unintentionally stopping messages from the sender from being processed. If you use strict: true, you should foresee the following mitigations:

• On the Receiver contract: You should be able to change the state of the dApp by taking out some restricting action, allowing for successful manual execution of the message. For example, you can implement a function enabling you to "skip" a specific message so that the rest of the messages can proceed.
• On the Sender contract: Give up on the messages that are in progress from the sender by upgrading the Sender contract.

The sender must make sure that the receiver is the correct one. Test without using strict: true first before setting it.

Evaluate the security and reliability of the networks that you use

Although CCIP has been thoroughly reviewed and audited, inherent risks might still exist based on your use case, the blockchain networks where you deploy your contracts, and the network conditions on those blockchains.

Review and audit your code

Before securing value with contracts that implement CCIP interfaces and routers, ensure that your code is secure and reliable. If you have a unique use case for CCIP that might involve additional cross-chain risk, contact the Chainlink Labs Team before deploying your application to mainnet.

Soak test your dApps

Be aware of the Service Limits and Rate Limits for Supported Networks. Before you provide access to end users or secure value, soak test your cross-chain dApps. Ensure that your dApps can operate within these limits and operate correctly during usage spikes or unfavorable network conditions.

Monitor your dApps

When you build applications that depend on CCIP, include monitoring and safeguards to protect against the negative impact of extreme market events, possible malicious activity on your dApp, potential delays, and outages.

Create your own monitoring alerts based on deviations normal activity. This will notify you when potential issues occur so you can respond to them.