> ## Documentation Index
> Fetch the complete documentation index at: https://docs.optimism.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Legacy Geth configuration options

> Reference for Legacy Geth (l2geth) environment variables and the RPC methods routed to it.

This page catalogues the environment variables Legacy Geth (`l2geth`) accepts and the RPC methods your execution client routes to it.
For what Legacy Geth is and how to set it up, see the [Legacy Geth guide](/node-operators/guides/configuration/legacy-geth).

Legacy Geth is required only for upgraded networks like OP Mainnet to serve historical execution traces from before the Bedrock upgrade.

## Environment variables

Legacy Geth accepts the following environment variables:

| Variable                   | Description                    | Default                               |
| -------------------------- | ------------------------------ | ------------------------------------- |
| `USING_OVM`                | **Required**. Enables OVM mode | N/A (must be set to `true`)           |
| `ETH1_SYNC_SERVICE_ENABLE` | Enables L1 sync service        | `true` (set to `false` for read-only) |
| `RPC_API`                  | Enabled RPC APIs               | `eth,net,web3`                        |
| `RPC_ADDR`                 | RPC listening address          | `localhost`                           |
| `RPC_CORS_DOMAIN`          | CORS domains                   | `localhost`                           |
| `RPC_ENABLE`               | Enable RPC server              | `false`                               |
| `RPC_PORT`                 | RPC port                       | `8545`                                |
| `RPC_VHOSTS`               | Virtual hosts                  | `localhost`                           |

<Warning>
  It is imperative that you specify the `USING_OVM=true` environment variable.
  Failing to specify this will cause `l2geth` to return invalid execution traces or panic at startup.
</Warning>

## Execution-client routing flag

Both op-reth and op-geth use the same `--rollup.historicalrpc` flag to route pre-Bedrock execution requests to Legacy Geth.
The flag takes the URL of the Legacy Geth RPC endpoint, for example `--rollup.historicalrpc=http://localhost:8545`.

## Historical execution vs. historical data

Only requests for **historical execution** will be routed to Legacy Geth.
Everything else will be served by your execution client directly.

### Historical execution RPC methods

These methods require transaction execution and are routed to Legacy Geth for pre-Bedrock blocks:

* `eth_call`
* `eth_estimateGas`
* `debug_traceBlockByNumber`
* `debug_traceBlockByHash`
* `debug_traceCall`
* `debug_traceTransaction`

### Historical data RPC methods

These methods only read data from the database and are served by your execution client:

* `eth_getBlockByNumber`
* `eth_getBlockByHash`
* `eth_getTransactionByHash`
* `eth_getTransactionReceipt`
* `eth_getLogs`