Custom Analyser for IPv4 Mapped IPv6

[Sai_Satwik_Kuppili]

Seems Elasticsearch doesn't allow IPv4 mapped IPv6 with CIDR to index. When I was trying to index IPv4-mapped-IPv6

::ffff:127.12.0.1/108

I am getting the following error.

PUT test
PUT test/_mapping/
{
    "dynamic_templates": [
        {
            "ip_range": {
                "match": "*ip_range",
                "mapping": {
                    "type": "ip_range",
                    "ignore_malformed": true
                }
            }
        }
    ]
}
PUT test/_doc/1
{
  "test1_ip_range": "::ffff:127.12.0.1/108"
}

{
    "error": {
        "root_cause": [
            {
                "type": "mapper_parsing_exception",
                "reason": "failed to parse field [test1_ip_range] of type [ip_range] in document with id '2'. Preview of field's value: '::ffff:127.12.0.1/108'"
            }
        ],
        "type": "mapper_parsing_exception",
        "reason": "failed to parse field [test1_ip_range] of type [ip_range] in document with id '2'. Preview of field's value: '::ffff:127.12.0.1/108'",
        "caused_by": {
            "type": "illegal_argument_exception",
            "reason": "CIDR notation is not allowed with IPv6-mapped IPv4 address [::ffff:127.12.0.1 as it introduces ambiguity as to whether the prefix length should be interpreted as a v4 prefix length or a v6 prefix length"
        }
    },
    "status": 400
}

But when I index IPv4, and when I query on IPv4 mapped IPv6, Elasticsearch query execution is working as expected.

Ex:

PUT test/_doc/2
{
  "test1_ip_range": "127.12.0.1/12"
}

GET test/_doc/_search
{
    "query": {
        "term": {
            "test1_ip_range": "::ffff:127.12.0.2"
        }
    }
}

In this case, search query returning expected results.
From the error thrown by the Elasticsearch, it seems IPv4-mapped IPv6 with CIDR cannot get indexed by Elasticsearch.

So I was thinking if we could write an custom analyser which can convert IPv4-mapped IPv6 with CIDR into IPv4 with CIDR before indexing.

Seems any IPv4 mapped IPv6 with CIDR can be converted to IPv4 by just removing prefix ::ffff: and by substracting 96 from CIDR value

Example: IPv4 for ::ffff:127.12.0.1/108 is 127.12.0.1/12.

Could someone help me if we can do this with custom analyser or by making some changes to Elasticsearch template? Any help is appreciated. Thanks in advance.