Ip2Asn 1.0.0

Ip2Asn

Offline IP → ASN lookup for .NET. Point it at an iptoasn.com TSV dump and resolve any IPv4 or IPv6 address to its AS number, country and AS name. No API keys, no network calls, no rate limits.

dotnet add package Ip2Asn

Get the data

Download ip2asn-combined.tsv.gz from iptoasn.com (covers IPv4 + IPv6). .gz files work as-is — no need to unpack.

Use it

using Ip2Asn;

// Load once at start-up, then reuse. Thread-safe for concurrent lookups.
var db = Ip2AsnDatabase.LoadFromTsv("ip2asn-combined.tsv");

if (db.TryLookup("142.250.199.132", out AsnRecord record))
{
    Console.WriteLine(record.Asn);          // 15169
    Console.WriteLine(record.CountryCode);  // US
    Console.WriteLine(record.Description);  // GOOGLE
    Console.WriteLine(record.RangeStart);   // 142.250.199.0
    Console.WriteLine(record.RangeEnd);     // 142.250.199.255
}

Other ways to ask:

uint? asn = db.GetAsn("142.250.199.132");           // 15169, or null
AsnRecord? hit = db.Lookup(IPAddress.Parse("1.1.1.1"));

Bulk

// A whole batch at once — large batches are spread across cores.
AsnLookupResult[] results = db.LookupBatch(logRows.Select(r => r.VisitedIp).ToList());

foreach (var r in results)
    Console.WriteLine($"{r.Input} -> {(r.Found ? "AS" + r.Record.Asn : "unknown")}");

// Or stream, for input too big to hold in memory.
foreach (var r in db.LookupMany(File.ReadLines("ips.txt")))
    Console.WriteLine($"{r.Input}\t{r.Asn}");

Accepted input

All of these resolve to the same answer — a port, CIDR prefix, zone id, brackets or surrounding whitespace are ignored:

142.250.199.132        142.250.199.132:443     142.250.199.132/24
::ffff:142.250.199.132   2606:4700::1          [2606:4700::1]:443
2606:4700::1/48        2606:4700::1%eth0        " 2606:4700::1 "

Unknown addresses

TryLookup returns false (and GetAsn returns null) both for input that isn't an address and for addresses nobody announces — private ranges like 10.250.14.7, reserved and unallocated space.

To tell those two apart, keep the dataset's "not routed" rows:

var db = Ip2AsnDatabase.LoadFromTsv("ip2asn-combined.tsv",
    new Ip2AsnOptions { SkipUnroutedRanges = false });

if (!db.TryLookup(ip, out AsnRecord r))  Console.WriteLine("not a valid IP");
else if (!r.IsRouted)                    Console.WriteLine("private / not routed");
else                                     Console.WriteLine($"AS{r.Asn} {r.Description}");

Faster start-up

Loading the 45 MB TSV takes ~380 ms. Convert it once to a binary index and load that instead:

Ip2AsnDatabase.LoadFromTsv("ip2asn-combined.tsv").SaveIndex("ip2asn.bin");

var db = Ip2AsnDatabase.LoadIndex("ip2asn.bin");   // ~155 ms, 15 MB file

ASP.NET Core

builder.Services.AddSingleton<IIp2AsnLookup>(
    _ => Ip2AsnDatabase.LoadFromTsv("ip2asn-combined.tsv"));

Options

Also available: LoadFromTsvAsync, LoadFromTsv(Stream), LoadFromTsv(TextReader), and Count / IPv4RangeCount / IPv6RangeCount / SkippedLineCount.

Numbers

Full ip2asn-combined.tsv (717k rows), .NET 8, one core unless noted:

Try it

dotnet run --project samples/Ip2Asn.Sample -- ip2asn-combined.tsv 1.1.1.1 8.8.8.8:443
cat ips.txt | dotnet run --project samples/Ip2Asn.Sample -- ip2asn-combined.tsv

Targets netstandard2.0 and net8.0. MIT licensed. The ip2asn dataset itself is published by iptoasn.com under its own terms and is not redistributed here.