Currently we bucket peers (or potential peers) based on /16 network groups which directly correlate to the IP-addresses. This is done to diversify connections every node maintains, for example to avoid connecting to the nodes all belonging to the same region/provider.

Currently peers.dat (serialized version of addrman) does not store ip->bucket mappings explicitly, and all the known ips from peers.dat are re-hashed and re-bucketed at every restart (although it's very cheap).

Idea

It was recently suggested by @TheBlueMatt to use ASN-based bucketing instead. This is strictly better because if the goal is to diversify connections: the distribution of IPs among the ASNs is not uniform, and because of that netgroup-based bucketing may result in having 8 peers from just 2 large ASNs.
If we allow connecting to each ASN at most once, this would increase the security of the network.

We have @sipa's script to create a compressed representation of mapping (ip->ASN), which is less than 2 megabytes.

However, there are integration-related design questions.

Distribution of the .map file

During the meeting there was a rough consensus (not unanimous though, @jnewbery ) that mapping file should be distributed along with the release, instead of becoming part of the binary.

If you want to question these, feel free to comment below.

Legacy /16 bucketing

There was a suggestion of having an old method as well. I think we should do it.

Loading the map

Maybe there will be concerns here, I have an understanding for now.