Go-Ethereum – Does –nodekey Work with Geth or Only Bootnode?

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.

There are a couple of issues here, that I hadn't outlined when I posted the question.

1. The first is that you may have other nodes running in your LAN that you may or may not be aware of - the external IP will be the same for all of them.
2. The second is that you should consider that being behind a router you want to route traffic to your node when it is required.
3. The third is that the question is more or less about being discovered on the network.

The question is therefore about if you want to host a permanent node or not.

Permanent Node

One reason to host a permanent node is if you want to host a bootnode for a network that can be connected to by anyone outside your LAN. You therefore need an external IP address, and you need to assure that there are no other nodes running behind your router that will also use the external IP address if not directly at least indirectly.

This solution in Parity requires setting the --nat extip:<your_external_ip> argument when you start up the node on the command line. This will force your node to startup and create an enode using your external IP and port.

This enode can then be included in your genesis.json file and will be used by other nodes to sync to the blockchain and other stuff.

Non-permanent node

This implies that you are starting and stopping your node at any time and you don't care too much about being available to the network or not.

Here you must consider what your router is doing. In this case you need to configure your router to have the port 30303 open (for ethereum or another value for your own private network) and port forwarding enabled for this port for both TCP and UDP.

This allows your node to both communicate with the network and be discoverable (UDP).