Ethereum_overview
Chapter 6: Ethereum Network & Ecosystem
Section titled “Chapter 6: Ethereum Network & Ecosystem”Overview
Section titled “Overview”Ethereum is the most widely-used blockchain for smart contracts and decentralized applications. Understanding Ethereum’s architecture is essential for any blockchain infrastructure engineer, as you’ll likely work with Ethereum nodes in production.
6.1 What is Ethereum?
Section titled “6.1 What is Ethereum?”Ethereum is a programmable blockchain that allows developers to build and deploy smart contracts and decentralized applications (dApps).
Key Facts
Section titled “Key Facts”| Attribute | Value |
|---|---|
| Launch Date | July 30, 2015 |
| Token | ETH (Ether) |
| Block Time | 12 seconds (PoS) |
| Consensus | Proof of Stake (after The Merge) |
| TPS | ~15-30 (L1); rollups scale to 100,000+ via blobspace (EIP-4844) |
| Gas Limit | 30 million gas per block |
6.2 Ethereum Network Types
Section titled “6.2 Ethereum Network Types”┌─────────────────────────────────────────────────────────────────┐│ ETHEREUM NETWORKS │├─────────────────────────────────────────────────────────────────┤│ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ MAINNET │ ││ │ Production - Real value, real applications │ ││ │ Chain ID: 1 │ ││ └─────────────────────────────────────────────────────────┘ ││ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ TESTNETWORKS │ ││ │ │ ││ │ Sepolia ─── New testnet (2022) ─── Recommended │ ││ │ Goerli ─── Old testnet (deprecated) │ ││ │ Holesky ─── Validator testnet │ ││ │ │ ││ └─────────────────────────────────────────────────────────┘ ││ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ LOCAL/PRIVATE NETWORKS │ ││ │ │ ││ │ Ganache, Hardhat, Besu (dev mode) │ ││ │ For local development and testing │ ││ └─────────────────────────────────────────────────────────┘ ││ │└─────────────────────────────────────────────────────────────────┘6.3 Ethereum: The Merge & Beyond
Section titled “6.3 Ethereum: The Merge & Beyond”Timeline of Upgrades
Section titled “Timeline of Upgrades”┌─────────────────────────────────────────────────────────────────────────────┐│ ETHEREUM UPGRADE TIMELINE │├─────────────────────────────────────────────────────────────────────────────┤│ ││ 2015 2016 2017 2019 2020 2022 2023 2024+ ││ │ │ │ │ │ │ │ │ ││ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ││ ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐ ││ │Frontier│ │Homestead│ │Metropolis│ │Istanbul│ │Beacon│ │Merge │ │Shapella│ │ ││ │ │ │ │ │ │ │ │ │Chain │ │ │ │ │ │Surge │ ││ └──────┘ └──────┘ └──────┘ └──────┘ └──────┘ └──────┘ └──────┘ ││ ││ Key Milestones: ││ - Frontier (2015): Initial release ││ - Homestead (2016): First upgrade ││ - The Merge (2022): PoW → PoS ││ - Shapella (2023): Staking withdrawals ││ - Dencun (2024): EIP-4844 blobs (proto-danksharding) for rollups ││ - Surge (roadmap): Rollups + (dan)ksharding, NOT chain-level sharding ││ │└─────────────────────────────────────────────────────────────────────────────┘Post-Merge Architecture
Section titled “Post-Merge Architecture”┌─────────────────────────────────────────────────────────────────────────────┐│ ETHEREUM POST-MERGE ARCHITECTURE │├─────────────────────────────────────────────────────────────────────────────┤│ ││ ┌────────────────────────────────────────────────────────────────────┐ ││ │ EXECUTION CLIENT │ ││ │ (Handles transactions, EVM, state) │ ││ │ │ ││ │ Geth / Erigon / Nethermind / Besu / Reth │ ││ │ │ ││ │ - Transaction Pool (Mempool) │ ││ │ - State Database │ ││ │ - EVM Execution │ ││ │ - Block Building │ ││ │ - JSON-RPC API │ ││ └────────────────────────────────┬───────────────────────────────────┘ ││ │ Engine API ││ ▼ ││ ┌────────────────────────────────────────────────────────────────────┐ ││ │ CONSENSUS CLIENT │ ││ │ (Handles PoS, Beacon Chain, validation) │ ││ │ │ ││ │ Lighthouse / Prysm / Teku / Nimbus / Lodestar │ ││ │ │ ││ │ - Beacon Chain │ ││ │ - Validator Management │ ││ │ - Fork Choice │ ││ │ - Attestations & Proposals │ ││ └────────────────────────────────────────────────────────────────────┘ ││ ││ Execution Client must connect to Consensus Client via Engine API ││ │└─────────────────────────────────────────────────────────────────────────────┘6.4 Ethereum Clients
Section titled “6.4 Ethereum Clients”Execution Clients
Section titled “Execution Clients”| Client | Language | Developers | Status |
|---|---|---|---|
| Geth | Go | Ethereum Foundation | Stable |
| Erigon | Go | Erigon Team | Stable |
| Nethermind | C#/.NET | Nethermind | Stable |
| Besu | Java | Hyperledger | Stable |
| Reth | Rust | Paradigm | Beta |
Consensus Clients
Section titled “Consensus Clients”| Client | Language | Developers | Status |
|---|---|---|---|
| Lighthouse | Rust | Sigma Prime | Stable |
| Prysm | Go | Prysmatic Labs | Stable |
| Teku | Java | ConsenSys | Stable |
| Nimbus | Nim | Status | Stable |
| Lodestar | TypeScript | ChainSafe | Stable |
6.5 Ethereum Virtual Machine (EVM)
Section titled “6.5 Ethereum Virtual Machine (EVM)”The EVM is a runtime environment for executing smart contracts on Ethereum.
EVM Architecture
Section titled “EVM Architecture”┌─────────────────────────────────────────────────────────────────┐│ ETHEREUM VIRTUAL MACHINE │├─────────────────────────────────────────────────────────────────┤│ ││ Smart Contract Bytecode ││ ┌─────────────────────────────────────────────────────────┐ ││ │ PUSH1 0x60 PUSH1 0x60 ADD PUSH1 0x00 SSTORE │ ││ └─────────────────────────────────────────────────────────┘ ││ │ ││ ▼ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ OPCODES │ ││ │ │ ││ │ Stack Operations: PUSH, POP, DUP, SWAP │ ││ │ Arithmetic: ADD, SUB, MUL, DIV, MOD │ ││ │ Comparison: LT, GT, EQ, ISZERO │ ││ │ Storage: SLOAD, SSTORE │ ││ │ Memory: MLOAD, MSTORE, MSIZE │ ││ │ Control: JUMP, JUMPI, JUMPDEST │ ││ │ Logging: LOG0, LOG1, LOG2, LOG3, LOG4 │ ││ │ System: CREATE, CALL, DELEGATECALL, STATICCALL │ ││ │ │ ││ └─────────────────────────────────────────────────────────┘ ││ │ ││ ▼ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ GAS CALCULATION │ ││ │ │ ││ │ Each opcode has a gas cost: │ ││ │ - ADD: 3 gas │ ││ │ - SLOAD: 2100 gas (cold) / 100 gas (warm) │ ││ │ - SSTORE: 20000 gas (set) / 5000 gas (modify) │ ││ │ - CALL: 2600 gas + value transfer │ ││ │ │ ││ └─────────────────────────────────────────────────────────┘ ││ │└─────────────────────────────────────────────────────────────────┘6.6 Gas & Fees
Section titled “6.6 Gas & Fees”Gas in Ethereum
Section titled “Gas in Ethereum”Gas is the unit of computation on Ethereum. Each operation requires a specific amount of gas.
┌─────────────────────────────────────────────────────────────────┐│ GAS MECHANICS │├─────────────────────────────────────────────────────────────────┤│ ││ Transaction Fee = Gas Used × Gas Price ││ ││ Components: ││ ┌─────────────────────────────────────────────────────────┐ ││ │ Gas Limit: Maximum gas you're willing to spend │ ││ │ (e.g., 21,000 for simple ETH transfer) │ ││ ├─────────────────────────────────────────────────────────┤ ││ │ Gas Used: Actual gas consumed by execution │ ││ ├─────────────────────────────────────────────────────────┤ ││ │ Gas Price: Price per unit of gas │ ││ │ - Base fee (network determined) + Priority fee │ ││ │ - Measured in Gwei (1 Gwei = 10^-9 ETH) │ ││ ├─────────────────────────────────────────────────────────┤ ││ │ Max Fee: Maximum you're willing to pay │ ││ │ - 2 * (base + priority) typically │ ││ └─────────────────────────────────────────────────────────┘ ││ ││ EIP-1559 (London Upgrade): ││ ┌─────────────────────────────────────────────────────────┐ ││ │ Base Fee: Burned, adjusts dynamically │ ││ │ Priority Fee: Goes to validator (tips) │ ││ │ │ ││ │ Formula: │ ││ │ total_fee = gas_limit * (base_fee + priority_fee) │ ││ └─────────────────────────────────────────────────────────┘ ││ │└─────────────────────────────────────────────────────────────────┘Gas Costs for Common Operations
Section titled “Gas Costs for Common Operations”| Operation | Gas Cost |
|---|---|
| Simple Transfer | 21,000 |
| ERC-20 Transfer | ~65,000 |
| Swap (Uniswap) | ~150,000-300,000 |
| Deploy Contract | ~1,000,000+ |
| Storage Write | 20,000+ |
6.7 Account Types
Section titled “6.7 Account Types”Ethereum has two types of accounts:
┌─────────────────────────────────────────────────────────────────┐│ ETHEREUM ACCOUNTS │├─────────────────────────────────────────────────────────────────┤│ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ EXTERNALLY OWNED ACCOUNT (EOA) │ ││ │ │ ││ │ - Controlled by private key │ ││ │ - Can send transactions │ ││ │ - Can hold ETH and tokens │ ││ │ - Has nonce (transaction counter) │ ││ │ │ ││ │ Address: 0x742d35Cc6634C0532925a3b844Bc9e7595f1e3E4 │ ││ └─────────────────────────────────────────────────────────┘ ││ ││ ┌─────────────────────────────────────────────────────────┐ ││ │ SMART CONTRACT ACCOUNT │ ││ │ │ ││ │ - Controlled by code (smart contract) │ ││ │ - Has executable code │ ││ │ - Has storage │ ││ │ - Can hold ETH and tokens │ ││ │ - Can be called by EOAs or other contracts │ ││ │ │ ││ │ Address: 0x... (created via CREATE/CREATE2) │ ││ └─────────────────────────────────────────────────────────┘ ││ ││ Both types have: balance, nonce, codeHash, storageRoot ││ │└─────────────────────────────────────────────────────────────────┘6.8 Transaction → Block Lifecycle
Section titled “6.8 Transaction → Block Lifecycle”Understanding the full journey of a transaction — from wallet to finalized block — is the single best way to show end-to-end understanding in an interview. Here is the Ethereum (post-Merge) flow.
The Journey of a Transaction
Section titled “The Journey of a Transaction”┌─────────────────────────────────────────────────────────────────┐│ TX → BLOCK LIFECYCLE (Ethereum, post-Merge) │├─────────────────────────────────────────────────────────────────┤│ ││ ┌─────────┐ ┌──────────┐ ┌──────────────────┐ ││ │ Wallet │───▶│ Mempool │───▶│ Block Proposal │ ││ │ dApp │ │(txpool) │ │ (CL + EL) │ ││ └─────────┘ └────┬─────┘ └────────┬─────────┘ ││ │ │ ││ ▼ ▼ ││ ┌──────────────┐ ┌──────────────────┐ ││ │ Propagation │ │ Execution │ ││ │ (devp2p) │ │ (EVM, state │ ││ │ │ │ root change) │ ││ └──────────────┘ └────────┬─────────┘ ││ ▼ ││ ┌──────────────────┐ ││ │ Broadcast block │ ││ │ + import by all │──────────────▶││ │ nodes │ ││ └────────┬─────────┘ ││ ▼ ││ ┌──────────────────┐ ││ │ Finality (Casper │ ││ │ FFG, ~2 epochs) │ ││ └──────────────────┘ ││ │└─────────────────────────────────────────────────────────────────┘Step by Step (Ethereum)
Section titled “Step by Step (Ethereum)”| Step | What happens | Where |
|---|---|---|
| 1. Submission | eth_sendRawTransaction — node checks signature, nonce, balance, gas, EIP-155 chain id | RPC layer → txpool |
| 2. Mempool entry | Tx lands in txpool_pending (or txpool_queued if nonce-gapped); relayed to peers via devp2p gossip | txpool, P2P |
| 3. Block building | The consensus client picks the next proposer; the EL builds the block payload (ordered txs, execution) and hands it to the CL via the Engine API | Engine API (engine_forkchoiceUpdatedV3, engine_getPayloadV3) |
| 4. Execution | EVM runs each tx: state transitions, gas metering, logs; per-tx receipts are produced | EVM / state trie |
| 5. State root | All state changes collapse into the world-state stateRoot committed in the new header | Patricia-Merkle trie (ch28) |
| 6. Broadcast/import | The CL-wide new block is gossiped; every other node validates (header, execution, state root) and imports it | P2P, block validation |
| 7. Finality | Casper FFG finalizes the block once two epochs of attestations reference it (~12.8 min); before that it is only justified and can be reorged | Consensus layer |
Interview talking point: “A transaction is included in a block after step 3, executed in step 4, canonical-but-reorgable after step 6, and final after step 7. When someone says ‘my tx is pending forever’, I check the txpool first (is it gossiping?), then gas/nonce, then whether the node is synced.”
Cross-Protocol Comparison
Section titled “Cross-Protocol Comparison”Different ecosystems move a tx to a block differently — never generalize Ethereum specifics to other chains:
| Protocol | Mempool | Who builds the block | Finality |
|---|---|---|---|
| Ethereum | txpool (gas-price ordered) | PoS proposer (CL selects, EL executes) | Casper FFG — final after ~2 epochs (~12.8 min) |
| Bitcoin | mempool (fee-rate ordered) | Miner solves PoW | Probabilistic — ~6 confirmations (~1 h) convention |
| Cosmos (CometBFT) | mempool | Round-robin proposer per height | Instant upon commit — 2/3+ precommits; reorgs possible only in rare pegged rounds |
| Solana | TPU ingest queue | Leader schedule (PoH) | Finalized after ~2 slots + confirmation (~a few hundred ms) |
| Polkadot | txpool | BABE slot producer for the relay chain | GRANDPA — finalizes in batches with authority-set signatures |
6.9 Interview Questions
Section titled “6.9 Interview Questions”| Question | Answer |
|---|---|
| What is The Merge? | Transition from PoW to PoS on Ethereum |
| What are execution vs consensus clients? | Execution handles transactions/EVM; consensus handles PoS |
| What is gas in Ethereum? | Unit of computation for transaction fees |
| What is EIP-1559? | London upgrade that burns base fees |
| Walk me through a transaction’s lifecycle | See 6.8: submit → mempool → proposal → execute → state root → broadcast → finality |
Summary
Section titled “Summary”- Ethereum is the leading smart contract platform
- Uses dual-client architecture (execution + consensus)
- Multiple client implementations exist for diversity
- Gas fees are paid in ETH (Gwei)
- Post-Merge uses Proof of Stake
Next Chapter
Section titled “Next Chapter”In Chapter 7: Geth Client - Setup & Configuration, we’ll dive into the most popular Ethereum client - Geth.
Last Updated: 2026-02-20