doc: Add initial asmap data documentation

doc/asmap-data.md

@@ -0,0 +1,59 @@
+# Embedded ASMap data
+
+## Background
+
+The ASMap feature (available via `-asmap`) makes it possible to use a peer's AS Number (ASN), an ISP/hoster identifier,
+in netgroup bucketing in order to ensure a higher diversity in the peer
+set. When not using this, the default behavior is to have the buckets formed
+based on IP prefixes but this does not
+prevent having connections dominated by peers at the same large-scale hoster,
+for example, since such companies usually control many diverse IP ranges.
+In order to use ASMap, the mapping between IP prefixes and AS Numbers needs
+to be available. This mapping data can be provided through an external file
+but Bitcoin Core also embeds a default map in its builds to make the feature
+available to users when they are unable to provide a file.
+
+## Data sourcing and tools
+
+ASMap is a mapping of IP prefix to ASN, essentially a snapshot of the
+internet routing table at some point in time. Due to the high volatility
+of parts of this routing table and the known vulnerabilities in the BGP
+protocol it is challenging to collect this data and prove its consistency.
+Sourcing the data from a single trusted source is problematic as well.
+
+The [Kartograf](https://github.com/asmap/kartograf) tool was created to
+deal with these uncertainties as good as possible. The mapping data is sourced from RPKI, IRR and
+Routeviews. The former two are themselves used as security mechanisms to
+protect against BGP security issues, which is why they are considered more secure and
+their data takes precedence. The latter is a trusted collector of BGP traffic
+and only used for IP space that is not covered by RPKI and IRR.
+
+The process in which the Kartograf project parses, processes and merges these
+data sources is deterministic. Given the raw download files from these
+different sources, anyone can build their own map file and verify the content
+matches with other users' results. Before the map is usable by Bitcoin Core
+it needs to be encoded as well. This is done using `asmap-tool.py` in `contrib/asmap`
+and this step is deterministic as well.
+
+When it comes to obtaining the initial input data, the high volatility remains
+a challenge if users don't want to trust a single creator of the used ASMap file.
+To overcome this, multiple users can start the download process at the exact
+same time which leads to a high likelihood that their downloaded data will be
+similar enough that they receive the same output at the end of the process.
+This process is regularly coordinated at the [asmap-data](https://github.com/asmap/asmap-data)
+project. If enough participants have joined the effort (5 or more is recommended) and a majority of the
+participants have received the same result, the resulting ASMap file is added
+to the repository for public use. Files will not be merged to the repository
+without at least two additional reviewers confirming that the process described
+above was followed as expected and that the encoding step yielded the same
+file hash. New files are created on an ongoing basis but without any central planning
+or an explicit schedule.
+
+## Release process
+
+As an upcoming release approaches the embedded ASMap data should be updated
+by replacing the `ip_asn.dat` with a newer ASMap file from the asmap-data
+repository so that its data is embedded in the release. Ideally, there may be a file
+already created recently that can be selected for an upcoming release. Alternatively,
+a new creation process can be initiated with the goal of obtaining a fresh map
+for use in the upcoming release.

doc/release-process.md

@@ -30,6 +30,7 @@ Release Process
 
 * Update translations see [translation_process.md](/doc/translation_process.md#synchronising-translations).
 * Update hardcoded [seeds](/contrib/seeds/README.md), see [this pull request](https://github.com/bitcoin/bitcoin/pull/27488) for an example.
+* Update embedded asmap data at `/src/node/data/ip_asn.dat`, see [asmap data documentation](./asmap-data.md).
 * Update the following variables in [`src/kernel/chainparams.cpp`](/src/kernel/chainparams.cpp) for mainnet, testnet, and signet:
   - `m_assumed_blockchain_size` and `m_assumed_chain_state_size` with the current size plus some overhead (see
     [this](#how-to-calculate-assumed-blockchain-and-chain-state-size) for information on how to calculate them).