IP2ASN

What is IP2ASN?

IP2ASN is a free service that maps IP addresses (both IPv4 and IPv6) to their origin Autonomous System Numbers (ASNs). An Autonomous System is a collection of IP networks and routers under the control of a single organization that presents a common routing policy to the internet.

REST API

Endpoint

GET /json?ip=<address>

Parameters

Response Format

Successful response (HTTP 200):

{
  "origins": [15169]
}

The origins array contains the unique ASNs found in the BGP routing table for the given IP address. Multiple ASNs may be returned if the IP is multi-homed.

Error Responses

Examples

cURL

curl https://ip2asn.net/json?ip=8.8.8.8

Python

import requests

response = requests.get('https://ip2asn.net/json?ip=8.8.8.8')
data = response.json()
print(f"ASNs: {data['origins']}")

JavaScript

fetch('https://ip2asn.net/json?ip=8.8.8.8')
  .then(response => response.json())
  .then(data => console.log('ASNs:', data.origins));

Go

resp, err := http.Get("https://ip2asn.net/json?ip=8.8.8.8")
if err != nil {
    log.Fatal(err)
}
defer resp.Body.Close()

var result struct {
    Origins []int `json:"origins"`
}
json.NewDecoder(resp.Body).Decode(&result)
fmt.Println("ASNs:", result.Origins)

Use Cases

• Network Analysis: Identify the network operator for any IP address
• Security Research: Track IP ownership and routing information
• Geolocation: Supplement IP geolocation with ASN data
• Monitoring: Track changes in BGP routing and network topology
• Abuse Prevention: Identify network sources of malicious traffic

Limitations

• Private, reserved, and multicast IP addresses are rejected (RFC 1918, RFC 4193, etc.)
• Backend timeout is 500ms - requests may fail if routing data is slow to retrieve
• No rate limiting at application level (handled by upstream proxy)
• Results reflect current BGP routing table state - may change over time
• No historical data or time-series analysis available

MCP Server

The service includes a Model Context Protocol (MCP) server at /mcp that exposes IP-to-ASN lookup functionality to AI assistants and other MCP clients.

MCP Tools

• lookup_asn - Look up origin AS numbers for an IP address

MCP Resources

• ip2asn://metrics - Service metrics information

Example MCP Request

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "lookup_asn",
    "arguments": {
      "ip": "8.8.8.8"
    }
  }
}

The MCP server follows the Model Context Protocol specification and supports initialize, tools/list, tools/call, resources/list, and resources/read methods.

Additional Endpoints

• /health - Health check endpoint

Service Metrics

Real-time service statistics: