How to trace routing in Angular 2?

You can pass in a second argument with options:

imports: [
    RouterModule.forRoot(
      routes,
      { enableTracing: true } // <-- debugging purposes only
    )
]

Angular will then log all events to the browser's console, per the documentation:

enableTracing?: boolean
When true, log all internal navigation events to the console. Use for debugging.

As the comments in the most accepted answer suggest, this enableTracing doesn't work in the forChild method. A simple work around is to subscribe to all routing events in AppModule like so:

export class AppModule {

  constructor(
    private readonly router: Router,
  ) {
    router.events
      .subscribe(console.log)
  }

}

Although I am late to answer this. But it might be useful to newbies in Angular.

There are two ways with which you can trace angular route changes.

1. RouterModule (enableTracing)

You can set enableTracing to RouterModule which will log you all the route change events.

RouterModule.forRoot(routes, { 
  enableTracing: true,    /* <-- Set this to true */
}),

2. Subscribe to Router.events

If you don't want to trace all the router change events then you can subscribe to Router.events. With which you can filter specific route change events.

constructor(
  private router: Router,
  /* Other dependencies */
) {

  this.router.events
    .pipe(
      // You can also use traditional if else in the subscribe 
      filter(event => event instanceof NavigationStart)
    )
    .subscribe(event => {
      console.group(`Router event: ${event.constructor.name}`);
      console.log(event);
      console.groupEnd();
    });
}

In addition to devqons excellent answer: Debugging your route definitions will be much easier if you temporarily out-comment wildcard routes. Wildcard routes are handy in production to show e.g. a NotFound component, but are a pain while debugging.

For example:

const routes: Routes = [
    ... (your route definions)

    // If you have a catch-all route defined, outcomment is like below
    // {
    //     path: '**',
    //     redirectTo: '/error/not-found',
    // },
];

After outcommenting your catch-all route, the router will not swallow your error and show in your browser console exactly what route could not be matched against your definitions.

For example, when the following error is shown:

core.js:4002 ERROR Error: Uncaught (in promise): Error: Cannot match any routes. URL Segment: 'projects/123'
Error: Cannot match any routes. URL Segment: 'projects/123'
    at ApplyRedirects.push../node_modules/@angular/router/fesm5/router.js.ApplyRedirects.noMatchError (router.js:2459)

you immediately known that there is a problem with matching 'projects/123' in your route definitions.