adding example for CIDR block in Data Prepper

_data-prepper/pipelines/cidrcontains.md

@@ -22,3 +22,82 @@ cidrContains('/client.ip', '192.168.0.0/16', '10.0.0.0/8')
 {% include copy.html %}
 
 This function returns `true` if the IP address matches any of the specified CIDR blocks or `false` if it does not.
+
+## Example
+
+The following pipeline drops any documents that are not part of the specified CIDR blocks:
+
+```yaml
+cidr-allowlist-pipeline:
+  source:
+    http:
+      path: /events
+      ssl: true
+      sslKeyCertChainFile: "certs/dp.crt"
+      sslKeyFile: "certs/dp.key"
+  processor:
+    - drop_events:
+        # Drop events whose client IP is NOT in specific CIDR allowlist
+        drop_when: 'not cidrContains(/client/ip, "10.0.0.0/8", "192.168.0.0/16", "fd00::/8")'
+  sink:
+    - opensearch:
+        hosts: ["https://opensearch:9200"]
+        insecure: true
+        username: admin
+        password: "admin_pass"
+        index_type: custom
+        index: "logs-%{yyyy.MM.dd}"
+```
+{% include copy.html %}
+
+You can test this pipeline using the following command:
+
+```bash
+curl -ksS -X POST "https://localhost:2021/events" \
+  -H "Content-Type: application/json" \
+  -d '[
+    {"client":{"ip":"10.23.45.6"},"msg":"allowed 10/8"},
+    {"client":{"ip":"8.8.8.8"},"msg":"should be dropped"},
+    {"client":{"ip":"fd00::1234"},"msg":"allowed ULA IPv6"}
+  ]'
+```
+{% include copy.html %}
+
+The documents stored in OpenSearch contain the following information:
+
+```json
+{
+  ...
+  "hits": {
+    "total": {
+      "value": 2,
+      "relation": "eq"
+    },
+    "max_score": 1,
+    "hits": [
+      {
+        "_index": "logs-2025.10.14",
+        "_id": "Ng1i4pkBLPEKXekW48BU",
+        "_score": 1,
+        "_source": {
+          "client": {
+            "ip": "10.23.45.6"
+          },
+          "msg": "allowed 10/8"
+        }
+      },
+      {
+        "_index": "logs-2025.10.14",
+        "_id": "Nw1i4pkBLPEKXekW48BU",
+        "_score": 1,
+        "_source": {
+          "client": {
+            "ip": "fd00::1234"
+          },
+          "msg": "allowed ULA IPv6"
+        }
+      }
+    ]
+  }
+}
+```