[Ethereum] Geth: bootnode tool and –nodiscover

I think it had previously been a part of the "Geth and Tools" release package, but it's gone missing... An issue was raised a couple of days ago: #3703

With regards to what it does, further up the page you linked to there's a description of each of the standalone tools (yes, they're separate executables):

bootnode

Stripped down version of our Ethereum client implementation that only takes part in the network node discovery protocol, but does not run any of the higher level application protocols. It can be used as a lightweight bootstrap node to aid in finding peers in private networks.

Finally it worked. I still don't really know what did it but I will list here some of the changes that got it to work. When I figure out what exactly did it I will update my answer.

• Use the --v5disc flag for node discovery.
• The bootnode took ages to start with the --v5 flag so instead of using a bootnode I chose a random node as bootnode. I started my node with the --bootnodes referring to this regular node but didn't seem to work until I manually added it. Probably using static-nodes.json would have worked as well.
• Use a small networkId. I think I was too optimistic on the size of this value. Once I ran geth and realized that it was using a different NetworkID from the one I entered. This was not a good sign but instead of choosing a smaller value I chose as the value that geth was suggesting. I only realized there was something wrong going on when I got this error Protocol eth/63 failed id=X conn=inbound err="NetworkId mismatch - 3853220132 (!= 1245324517197969700)". I am now using a 10-digit networkId and this is what seems to have done the trick.
• [Possibly not necessary] Run a node in miner mode (personal.newAccount("pw"), miner.setEtherbase(eth.accounts[0]) & miner.start())

I am more inclined to think it was the networkId that was causing some sort of problem. At least switching to v5 made it more easy to detect.