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+# Creating Cardano testnets 
+
+In [Shelley genesis](shelley-genesis.md) we discussed how to manually create a Shelley blockchain
+and how to create a testnet semi-automatically using the `cardano-cli genesis create` command. That explainer
+did not cover the steps needed to create a testnet that starts in the Byron era and is updated to the latest
+era. This process requires a fair amount of manual work: converting genesis and delegate keys from Byron to
+Shelley, creating genesis files, handling file hashing, manually updating the configuration file, etc.
+
+Creating a testnet that starts in Byron and can transition to Shelley and later eras is possible with the
+`cardano-cli genesis create-cardano` command. Note that on mainnet, we need to use the manual method
+described in [Shelley genesis](shelley-genesis.md).
+
+The `create-cardano` command automatically generates the Byron, Shelley and Alonzo genesis files, including
+the needed genesis keys, delegate keys, and UTXO keys. This command also handles all the hashing and
+generates the configuration file for the node.
+
+The `create-cardano` command also requires us to provide template files for the node configuration file,
+Byron genesis, Shelley genesis and Alonzo genesis. These template files contain the parameters needed for
+the testnet, all eras, and the configuration file for the nodes. You can find template files in the
+[cardano-world repository](https://github.com/input-output-hk/cardano-world/tree/master/nix/cardano/environments/testnet-template)
+and adjust them to your needs.
+
+By calling help for `create-cardano`, you will see the needed parameters:
+
+```bash
+$ cardano-cli genesis create-cardano
+
+--genesis-dir DIR        The genesis directory containing the genesis template
+                         and required genesis/delegation/spending keys.
+--gen-genesis-keys INT   The number of genesis keys to make [default is 3].
+--gen-utxo-keys INT      The number of UTXO keys to create [default is 0].
+--start-time UTC-TIME    The genesis start time in YYYY-MM-DDThh:mm:ssZ
+                         format. If unspecified, will be the current time +30
+                         seconds.
+--supply LOVELACE        The initial coin supply in lovelace which will be
+                         evenly distributed across initial, non-delegating
+                         stake holders.
+--security-param INT     Security parameter for the genesis file [default is 108].
+--slot-length INT        Slot length (ms) parameter for genesis file [default
+                         is 1000].
+--slot-coefficient RATIONAL
+                         Slot coefficient for the genesis file [default is .05].
+--mainnet                Use the mainnet magic ID.
+--testnet-magic NATURAL  Specify a testnet magic ID.
+--byron-template FILEPATH
+                         JSON file with genesis defaults for each Byron.
+--shelley-template FILEPATH
+                         JSON file with genesis defaults for each Shelley.
+--alonzo-template FILEPATH
+                         JSON file with genesis defaults for each Alonzo.
+--node-config-template FILEPATH
+                         The node config template
+
+```
+
+There are also a few things to consider:
+
+* The _maximum supply_ is hardcoded to 45 billion ada (like on mainnet). The amount in `--supply` is distributed evenly across initial UTXO keys. The difference between 45 billion and `--supply` will be available on the _Reserves_ when updating to the Shelley era.
+
+* `--slot-length`, `--security-param` and `--slot-coefficient` together determine the epoch length on the resulting network. Byron epochs last _10k_ slots, and Shelley epochs last _10k/f_ slots. Where _k_ is the security parameter and _f_ is the slot coefficient.
+
+### Example
+
+For a network with three genesis keys, three delegate nodes, two non-delegated UTXO keys with five billion each and 10 minutes epochs, run:
+
+```bash
+$ cardano-cli genesis create-cardano \
+--genesis-dir cluster \
+--gen-genesis-keys 3 \
+--gen-utxo-keys 2 \
+--supply 10000000000000000 \
+--security-param 300 \
+--slot-length 100 \
+--slot-coefficient 5/100 \
+--testnet-magic 42 \
+--byron-template byron.json \     
+--shelley-template shelley.json \
+--alonzo-template alonzo.json \
+--node-config-template config.json
+```
+
+This creates the following:
+
+* The 'cluster' directory
+* Byron, Shelley and Alonzo genesis files
+* The node configuration file
+* Three Byron era genesis keys
+* Three Shelley era genesis keys (converted from Byron keys)
+* Three delegate Byron keys
+* Three delegation certificates
+* Three operational certificates and operational certificate counters
+* Three cold, KES, and VRF keys
+* Two Byron era non-delegated UTXO keys
+* Two Shelley era UTXO keys (converted from Byron keys)  
+
+```bash
+$ tree cluster/
+cluster/
+├── alonzo-genesis.json
+├── byron-genesis.json
+├── delegate-keys
+│   ├── byron.000.cert.json
+│   ├── byron.000.key
+│   ├── byron.001.cert.json
+│   ├── byron.001.key
+│   ├── byron.002.cert.json
+│   ├── byron.002.key
+│   ├── shelley.000.counter.json
+│   ├── shelley.000.kes.skey
+│   ├── shelley.000.kes.vkey
+│   ├── shelley.000.opcert.json
+│   ├── shelley.000.skey
+│   ├── shelley.000.vkey
+│   ├── shelley.000.vrf.skey
+│   ├── shelley.000.vrf.vkey
+│   ├── shelley.001.counter.json
+│   ├── shelley.001.kes.skey
+│   ├── shelley.001.kes.vkey
+│   ├── shelley.001.opcert.json
+│   ├── shelley.001.skey
+│   ├── shelley.001.vkey
+│   ├── shelley.001.vrf.skey
+│   ├── shelley.001.vrf.vkey
+│   ├── shelley.002.counter.json
+│   ├── shelley.002.kes.skey
+│   ├── shelley.002.kes.vkey
+│   ├── shelley.002.opcert.json
+│   ├── shelley.002.skey
+│   ├── shelley.002.vkey
+│   ├── shelley.002.vrf.skey
+│   └── shelley.002.vrf.vkey
+├── genesis-keys
+│   ├── byron.000.key
+│   ├── byron.001.key
+│   ├── byron.002.key
+│   ├── shelley.000.skey
+│   ├── shelley.000.vkey
+│   ├── shelley.001.skey
+│   ├── shelley.001.vkey
+│   ├── shelley.002.skey
+│   └── shelley.002.vkey
+├── node-config.json
+├── shelley-genesis.json
+└── utxo-keys
+   ├── byron.000.key
+   ├── byron.001.key
+   ├── shelley.000.skey
+   ├── shelley.000.vkey
+   ├── shelley.001.skey
+   └── shelley.001.vkey
+
+4 directories, 53 files
+```
+
+Starting the cluster requires topology files for each of the nodes. For example:
+
+```JSON
+{
+   "Producers": [
+     {
+       "addr": "127.0.0.1",
+       "port": 3001,
+       "valency": 1
+     },
+     {
+       "addr": "127.0.0.1",
+       "port": 3002,
+       "valency": 1
+     }
+   ]
+ }
+```
+Note: For details about topology files please refer to [Understanding configuration files](../getting-started/understanding-config-files.md).
+
+
+Then, run the nodes with block production keys, for example:
+
+```bash
+$ cardano-node run \
+--config node-config.json \
+--topology topology.json \
+--database-path db \
+--socket-path node.socket \
+--port 3000 \
+--delegation-certificate delegate-keys/byron.000.cert.json \
+--signing-key delegate-keys/byron.000.key
+```  
+
+Updating the testnet to later eras can be done using update proposals, please refer to [Cardano governance](./cardano-governance.md) to learn how to do it.