What the Plugin Does

Architecture

                         +--------------------------+
                         |        CoreDNS           |
                         |   (asnlookup plugin)     |
                         +------------+-------------+
                                      |
                     +----------------+------------------+
                     |                                   |
             Request from ASN 58820               Request from ASN ≠ 58820
            (APIK NETWORKS / Jakarta)                (ex: Telkomsel)
                     |                                   |
       +-------------+-------------+         +-----------+-------------+
       |                           |         |                         |
       v                           |         v                         |
+-------------+                    |   +-------------+                 |
| ASN Lookup  | -- returns --> 58820   | ASN Lookup  | -- returns --> 23693
+-------------+                        +-------------+                 
       |                                        |
       v                                        v
+---------------------------+        +---------------------------+
| Use Zone: example.com.cgk |        | Use Zone: example.com.jog |
| Location: Jakarta (CGK)   |        | Location: Yogyakarta (Jog)|
+-------------+-------------+        +-------------+-------------+
              |                                       |
              v                                       v
   +-----------------------+                +-----------------------+
   | Answer A record:      |                | Answer A record:      |
   |   cdn.example.com --> |                |   cdn.example.com --> |
   |         8.8.8.8       |                |         1.1.1.1       |
   +-----------------------+                +-----------------------+

                       Log Samples (when requests arrive)
                       ---------------------------------
   [INFO] plugin/asnlookup: IP 103.136.17.82 → ASN 58820 (APIK NETWORKS)
   [INFO] plugin/asnlookup: IP 182.0.140.171 → ASN 23693 (Telkomsel)

The asnlookup plugin allows you to retrieve ASN data associated with an IP address. This plugin uses the MaxMind GeoLite2 ASN database to map IP addresses to their ASN and associated organization.

The retrieved data is added to the request context using the metadata plugin. You can then access it programmatically, for example:

import (
    "github.com/coredns/coredns/plugin/metadata"
)
// ...
if getASN := metadata.ValueFunc(ctx, "asnlookup/asn"); getASN != nil {
    fmt.Printf("ASN: %s\n", getASN())
} else {
    fmt.Println("ASN metadata is not set.")
}
// ...

Database

The plugin supports the GeoLite2 ASN database. Ensure you update the database regularly for accurate results.

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