/b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)b/

export class AppComponent implements OnInit {

      testForm: FormGroup;
      constructor(private fb: FormBuilder) {}

      ngOnInit(): void {
        const ipPattern =
        '/b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)b/';
        this.testForm = this.fb.group({
          inp: ['128.129.80.66', Validators.pattern(ipPattern)]
        });
      }
    }

<form novalidate [formGroup]="testForm">
  <input formControlName="inp"/>
  {{testForm.status}}
</form>

const ipPattern =
    "(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)";