Howard Wu

I would advocate for `allow-external-peers` or `no-external-peers` (preferred) as the default flag

`--allow-external-peers` works for me. This means the default behavior is to not allow external peers. @joske can you update this PR to reflect this change?

> Yes, was waiting for confirmation on the final name :) Please see above: --allow-external-peers is confirmed

@joske can you update all instances of `false` to `true`? This includes the tests.

You'll want to do the same for the `Message` type as well.

Note for future readers: Setting to 5 blocks (from 1 block) would improve sync times, however if a range of blocks contain several large transactions, this could cause a spillover...

@raychu86 we could further improve the design: We could allow `BlockRequest` to send say `100` to `200`. The receiver could choose to send say `3` chunks of `BlockResponse` (i.e. `100-121`,...

At 5 block chunks, I can confirm that 1000 blocks (i.e. 3 hours of blocks) syncs in 30 minutes. So 24 hours of blocks syncs in 4 hours based on...

> Are there any benchmark testing that we can perform before doing this change? Yes, this PR is far from ready in my view. We still need to expand `BlockResponse`...

Can this be per IP?