feat: add support for NetBox custom fields

README.md

@@ -33,6 +33,23 @@ To create A/AAAA records for octoDNS, you need to manage the mapping between IP
 
 Starting with [Netbox v2.6.0](https://github.com/netbox-community/netbox/issues/166), Netbox now has a `dns_name` field in IP address records. But we **do not** use this field by default because this `dns_name` field can only store **single** FQDN. To use a `dns_name` field, set `field_name: dns_name` in [the configuration](#examples).
 
+### Custom fields
+
+You can also use NetBox custom fields to store DNS names. This is useful when you want to keep the `dns_name` field for the primary hostname and use a custom field for additional aliases.
+
+To use a custom field, prefix the field name with `cf_`. For example, if you have a custom field named `additional_dns` on IP addresses, configure it as:
+
+```yaml
+providers:
+  netbox-aliases:
+    class: octodns_netbox.NetboxSource
+    url: https://ipam.example.com
+    token: env/NETBOX_TOKEN
+    field_name: cf_additional_dns
+```
+
+The custom field should contain comma-separated FQDNs, just like the `description` field.
+
 ### PTR records
 
 `octodns-netbox` also supports PTR records. By default, only the first FQDN in the field is used to generate the PTR record, but you can enable multiple PTR records for a single IP by setting the `multivalue_ptr` parameter to `true` in [the configuration](#examples).
@@ -92,6 +109,10 @@ providers:
     # The `description` does not have any limitations so by default
     # we use the `description` field to store multiple FQDNs, separated by commas.
     # Other tested values are `dns_name`.
+    #
+    # Custom fields are also supported by using the `cf_` prefix.
+    # For example, if you have a custom field named `additional_dns`,
+    # set `field_name: cf_additional_dns`.
     field_name: description
 
     # Tag Name (Optional)

octodns_netbox/__init__.py

@@ -299,7 +299,7 @@ def _build_ptr_records(
             )
             # Potentially multiple FQDNs in the designated field
             fqdns = self._parse_fqdns_list(
-                ipam_record[self.field_name],
+                self._get_field_value(ipam_record),
                 len_limit=None if self.multivalue_ptr else 1,
             )
             for fqdn in fqdns:
@@ -385,7 +385,7 @@ def _build_records_for_ipam_record(
         record_type: Literal["A", "AAAA"] = "A" if ip_address.version == 4 else "AAAA"
 
         # Parse out any FQDNs listed in the desired NetBox field
-        fqdns = self._parse_fqdns_list(ipam_record[self.field_name])
+        fqdns = self._parse_fqdns_list(self._get_field_value(ipam_record))
 
         # For each FQDN, determine if it belongs to this zone and create records
         for fqdn in fqdns:
@@ -465,3 +465,30 @@ def _parse_fqdns_list(
             if fqdn.strip()
         ]
         return fqdns[:len_limit] if len_limit else fqdns
+
+    def _get_field_value(self, ipam_record: typing.Any) -> str:
+        """
+        Retrieves the value of the configured field from an IPAM record.
+
+        Supports both standard fields (e.g., 'dns_name', 'description') and
+        custom fields (prefixed with 'cf_'). Custom fields are accessed via
+        the 'custom_fields' dictionary on the IPAM record.
+
+        Args:
+            ipam_record (Any): A single IPAM record from NetBox.
+
+        Returns:
+            str: The field value, or an empty string if the field is not set.
+
+        Examples:
+            - field_name='dns_name' -> ipam_record['dns_name']
+            - field_name='cf_additional_dns' -> ipam_record.custom_fields['additional_dns']
+        """
+        if self.field_name.startswith("cf_"):
+            # Custom field: strip 'cf_' prefix and access via custom_fields
+            custom_field_name = self.field_name[3:]
+            custom_fields = getattr(ipam_record, "custom_fields", {}) or {}
+            return custom_fields.get(custom_field_name, "") or ""
+        else:
+            # Standard field: access directly
+            return ipam_record[self.field_name] or ""