A blog post from the Ethereum Foundation was recently released regarding the testnet Morden. The testnet has been reset, so Morden is no more. The new testnet is called Ropsten. Morden was named for a terminus subway station in London, and Ropsten is another end station on a subway, but located in Stockholm, Sweden.
Talk of resetting the testnet had already been going on in the Ethereum community, mainly because restarting the test network from a new genesis block would enable clients to fully sync to the network more easily. A shorter blockchain makes syncing less resource intensive since there is less information to download. Also, due to the difficulty bomb (which will eventually force Ethereum to switch from a Proof-of-Work protocol to a Proof-of-Stake model), the block times were increasing on the testnet due to the low difficulty of mining on Morden. Block times would have only continued to grow, so an eventual restart was inevitable.
The Morden testnet was always eventually going to be reset, but it was a recent consensus issue that caused the testnet to be restarted, and reborn as Ropsten. Ropsten is an entirely new blockchain, started from its own genesis block. The issue that lead to the quick implementation of this new testnet was on the old testnet only, and was related to hard fork No. 4.
With the upcoming Spurious Dragon hard fork, the Morden testnet was set to fork first, at block 1,885,000. The reason to fork the testnet first was to ensure implementing the hard fork in the main net would go smoothly. While the fork occurred as planned, there was a small issue that later arose. At block 1,885,074 there was a consensus issue between Geth and Parity. The issue sprung from replay-attack protection and new rules (proposed in EIP 161) regarding nonces. The Ethereum blog post explains:
“The Morden testnet has been running since the launch of the Ethereum blockchain (July 2015). At that time, concerns about replay-attacks between Morden and Mainnet were addressed by using a nonce-offset. All accounts on Morden used a starting nonce of 2^20 instead of 0, ensuring that any transaction valid on one chain would not be valid on the other.
EIP 161 specifies new EVM rules regarding nonces. The implementation of those rules, in combination with Morden-specific nonce-rules, resulted in Geth and Parity creating incompatible blocks at block 1885074.”
While consensus issues between Ethereum clients would normally be a serious problem, these issues were specific to the Morden testnet only. There are no known issues that would affect the main net.
So the Spurious Dragon hard fork should occur without issue, and now that the testnet is reset (and rebranded Ropsten), it should be functioning normally as well. For any developers looking to start working on Ropsten, the genesis file can be downloaded here.
ETHNews will be actively following this story for potential updates.