ngonit method of component getting called twice which holds the router-outlet

I have a route requirement like localhost:4200/1234 where 1234 is mapped to adNo.

And i have child route like localhost:4200/ad1 and localhost:4200/ad2. landComponent oninit method gets the parameter and decides where it has to redirect internally.

Issue is that oninit method is called twice when page is loaded first i.e when localhost:4200/1234 is loaded, how can this be prevented.Calling twice happens when navigateByUrl is invoked. Below is the route code.

Root Route
export const appRoutes: Routes = [
  { path: ':adNo', component: landComponent },
];

Child Route

export const subRoutes: Routes = [
  {
    path: '',
    component: landComponent,
    children: [{ path: 'ad1', component: infoComponent },
    { path: 'ad2', component: typeComponent }]
  }
];

LandComponent
ngOnInit() {    
   // logic to get the adNo and make service call
  let adNo = this._activatedRoute.snapshot.params['adNo'];
   console.log('working');
   this._router.navigateByUrl('ad1', { skipLocationChange: true });
}