Fixes #3722: Allow the underscore character in IPAddress DNS names

docs/release-notes/version-2.6.md

@@ -6,6 +6,7 @@
 * [#3457](https://github.com/netbox-community/netbox/issues/3457) - Display cable colors on device view
 * [#3329](https://github.com/netbox-community/netbox/issues/3329) - Remove obsolete P3P policy header
 * [#3663](https://github.com/netbox-community/netbox/issues/3663) - Add query filters for `created` and `last_updated` fields
+* [#3722](https://github.com/netbox-community/netbox/issues/3722) - Allow the underscore character in IPAddress DNS names
 
 ## Bug Fixes
 

netbox/ipam/validators.py

@@ -2,7 +2,7 @@ from django.core.validators import RegexValidator
 
 
 DNSValidator = RegexValidator(
-    regex='^[0-9A-Za-z.-]+$',
-    message='Only alphanumeric characters, hyphens, and periods are allowed in DNS names',
+    regex='^[0-9A-Za-z.-_]+$',
+    message='Only alphanumeric characters, hyphens, periods, and underscores are allowed in DNS names',
     code='invalid'
 )