<div class="ui-inputgroup">
  <span style="margin-right: 18px">{{title}} </span>
  <input [disabled]="fixed >= 0"type="text" pInputText placeholder="127" maxlength="3" [(ngModel)]="first" value="{{first}}" (keyup)="onIpInput($event)">
  <span class="ui-inputgroup-addon">.</span>
  <input [disabled]="fixed > 1" type="text" pInputText placeholder="0" maxlength="3" [(ngModel)]="second" value="{{second}}" (keyup)="onIpInput($event)">
  <span class="ui-inputgroup-addon">.</span>
  <input [disabled]="fixed > 2" type="text" pInputText placeholder="0" maxlength="3" [(ngModel)]="third" value="{{third}}" (keyup)="onIpInput($event)">
  <span class="ui-inputgroup-addon">.</span>
  <input type="text" pInputText placeholder="1" maxlength="3" [(ngModel)]="fourth" value="{{fourth}}" (keyup)="onIpInput($event)">
</div>