RouterModule não exporta corretamente

Opa, No app.routing.module.ts o módulo RouterModule quando exportado não funciona. Tive que importa-lo manualmente no app.module. Pode ser algum erro tosco meu de sintaxe.

app.routing.module.ts:

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';

import { PhotoListComponent } from './photos/photo-list/photo-list.component';
import { PhotoFormComponent } from './photos/photo-form/photo-form.component';

const routes: Routes = [
    { path:'p/add' , component:PhotoFormComponent }, 
    { path:'user/flavio', component: PhotoListComponent}
];


@NgModule({
    imports:[RouterModule.forRoot(routes)],
    exports: [RouterModule]

})

export class AppRoutingModule{}

app.module.ts:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app.routing.module';
import { AppComponent } from './app.component';
import { PhotosModule } from './photos/photos.module';
import { RouterModule } from '@angular/router';


@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    RouterModule,
    AppRoutingModule,
    PhotosModule,
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }