Ethereum networks (mainnet, testnet) in Blockchain / Solidity

Introduction

Ethereum networks let you run and test blockchain programs safely. The mainnet is the real network with real money. Testnets are practice networks where you can try things without risk.

When you want to deploy a real Ethereum app that users will use with real money.

When you want to test your smart contract code without spending real Ether.

When you want to learn how Ethereum works without risking funds.

When you want to simulate transactions and see how your app behaves before going live.

Syntax

Blockchain / Solidity

network = 'mainnet'  # or 'testnet' like 'goerli', 'sepolia', 'rinkeby'

The mainnet is the live Ethereum network with real value.

Testnets like goerli or sepolia are copies of Ethereum for testing.

Examples

This sets the network to mainnet for real transactions.

Blockchain / Solidity

network = 'mainnet'
print(f"Connected to {network} - real Ethereum network")

This sets the network to Goerli testnet to test without real money.

Blockchain / Solidity

network = 'goerli'
print(f"Connected to {network} - test network for safe testing")

Sample Program

This program shows how to connect to different Ethereum networks and explains their purpose.

Blockchain / Solidity

def connect_to_network(network):
    if network == 'mainnet':
        return 'Connected to Ethereum mainnet with real Ether'
    elif network in ['goerli', 'sepolia', 'rinkeby']:
        return f'Connected to {network} testnet for safe testing'
    else:
        return 'Unknown network'

# Example usage
print(connect_to_network('mainnet'))
print(connect_to_network('goerli'))
print(connect_to_network('unknown'))

Important Notes

Always test your smart contracts on testnets before deploying to mainnet to avoid losing real money.

Testnets use fake Ether that you can get for free from faucets.

Mainnet transactions cost real Ether and are permanent.

Summary

Mainnet is the real Ethereum network with real value.

Testnets are safe places to practice and test your code.

Use testnets first, then deploy to mainnet when ready.

Practice

1. Which Ethereum network should you use to test your smart contracts without risking real money?

easy

A. Private network

B. Mainnet

C. Testnet

D. Production network

Solution

1. Step 1: Understand the purpose of testnets

   Testnets are designed for testing and development without real value at risk.

2. Step 2: Compare with mainnet

   Mainnet is the live network where real transactions and value exist, so testing there risks real money.

3. Final Answer:

   Testnet -> Option C

4. Quick Check:

   Testnet = Safe testing network [OK]

Hint: Testnets are for safe practice, mainnet is for real use [OK]

Common Mistakes:

• Confusing mainnet with testnet
• Thinking private network is the default test environment
• Assuming production network is safe for testing

2. Which of the following is the correct way to specify the Ethereum mainnet network ID in your configuration?

easy

A. "networkId": 1

B. "networkId": 3

C. "networkId": 42

D. "networkId": 4

Solution

1. Step 1: Recall Ethereum network IDs

   Mainnet uses network ID 1, testnets have other IDs like 3 (Ropsten), 4 (Rinkeby), 42 (Kovan).

2. Step 2: Match the ID to mainnet

   Network ID 1 corresponds to the Ethereum mainnet.

3. Final Answer:

   "networkId": 1 -> Option A

4. Quick Check:

   Mainnet networkId = 1 [OK]

Hint: Mainnet always uses network ID 1 [OK]

Common Mistakes:

• Using testnet IDs for mainnet
• Confusing networkId with chainId
• Assuming networkId 0 is valid

3. Given the following code snippet to connect to an Ethereum network, what network will it connect to?

const provider = new ethers.providers.JsonRpcProvider("https://rinkeby.infura.io/v3/YOUR_PROJECT_ID");
const network = await provider.getNetwork();
console.log(network.name);

medium

A. "mainnet"

B. "rinkeby"

C. "ropsten"

D. "kovan"

Solution

1. Step 1: Identify the RPC URL

   The URL contains "rinkeby.infura.io", indicating the Rinkeby testnet.

2. Step 2: Understand provider.getNetwork()

   This method returns the network info based on the RPC URL, so it will return "rinkeby".

3. Final Answer:

   "rinkeby" -> Option B

4. Quick Check:

   RPC URL domain = rinkeby [OK]

Hint: Check the RPC URL domain for network name [OK]

Common Mistakes:

• Assuming default is mainnet
• Confusing testnet names
• Ignoring the URL and guessing

4. You wrote this code to deploy a contract on Ropsten testnet but get an error:

const provider = new ethers.providers.JsonRpcProvider("https://mainnet.infura.io/v3/YOUR_PROJECT_ID");
const signer = provider.getSigner();
// deploy contract code here

What is the main issue?

medium

A. Incorrect contract deployment syntax

B. Provider does not support getSigner()

C. Using mainnet RPC URL instead of Ropsten testnet URL

D. Missing private key for signer

Solution

1. Step 1: Examine the signer line

   JsonRpcProvider.getSigner() fails because public RPC providers like Infura do not expose signing accounts or private keys.

2. Step 2: Correct approach for deployment

   Create a wallet signer: const wallet = new ethers.Wallet('0x-your-private-key', provider); const signer = wallet.connect(provider);

3. Final Answer:

   Missing private key for signer -> Option D

4. Quick Check:

   Use Wallet(privateKey, provider) for signing [OK]

Hint: Use ethers.Wallet(privateKey, provider) for signing deployments [OK]

Common Mistakes:

• Using provider.getSigner() without wallet
• Assuming getSigner() works without wallet
• Overlooking private key requirement

5. You want to write a script that deploys a smart contract first on the Goerli testnet and then on the mainnet only if tests pass. Which approach correctly handles this?

hard

A. Deploy on Goerli testnet, run tests, then deploy on mainnet if tests pass

B. Deploy on mainnet first, then test on Goerli

C. Deploy simultaneously on both networks

D. Deploy only on mainnet and skip testnet

Solution

1. Step 1: Understand deployment best practices

   Testnets like Goerli are used to test contracts safely before mainnet deployment.

2. Step 2: Apply conditional deployment logic

   Deploy on Goerli, run tests, and only deploy on mainnet if tests succeed to avoid costly errors.

3. Final Answer:

   Deploy on Goerli testnet, run tests, then deploy on mainnet if tests pass -> Option A

4. Quick Check:

   Test on testnet before mainnet deployment [OK]

Hint: Test on Goerli first, then deploy mainnet if tests pass [OK]

Common Mistakes:

• Deploying on mainnet before testing
• Skipping testnets entirely
• Deploying on both networks at once