What is the oldest Node that could still connect to the network (v0.9.1)?
The oldest nodes I've found to date [have been v0.9.1](https://bitnodes.io/nodes/leaderboard/?q=Satoshi%3A0.9.1). Based on protocol rules and backward compatibility, what is the oldest node that would be allowed on the network? Was there something between 0.8.0 and 0.9.1 that broke older clients?
I'm interested in the old clients as an educational exercise. v0.1.5 is only 20k lines and very simple to understand. v0.9.1 is 71k lines and much harder to get my head around. v0.20.1 is 200k lines and well beyond what I can simply passively study.
Any thoughts on creating a bitcoin time machine? Any ideas on how to get something like that off the ground? Could I just `dd` the genesis block by hand for those older version and just set up a VLAN with two nodes?
* Old bins: https://bitcoincore.org/bin/
* Old source: https://github.com/bitcoin/bitcoin/tags?after=v0.2.9