Umbraco URL Provider for frontpage set in "the ultimate site structure" (https://cultiv.nl/blog/tip-of-the-week-the-ultimate-site-structure-setup/)

FrontpageUrlProvider.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Umbraco.Core;
using Umbraco.Web;
using Umbraco.Web.Routing;

namespace MyWebsite.Core.UrlProviders
{
    public class FrontpageUrlProviderApplicationEventHandler : ApplicationEventHandler
    {
        protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            UrlProviderResolver.Current.InsertTypeBefore<DefaultUrlProvider, FrontpageUrlProvider>();
        }
    }

    public class FrontpageUrlProvider : IUrlProvider
    {
        public string GetUrl(UmbracoContext umbracoContext, int id, Uri current, UrlProviderMode mode)
        {
            var content = umbracoContext.ContentCache.GetById(id);
            if (content != null && content.AncestorOrSelf(1).HasValue("umbracoInternalRedirectId") && content.AncestorOrSelf(1).GetProperty("umbracoInternalRedirectId").DataValue.ToString() == content.Id.ToString())
            {
                return content.AncestorOrSelf(1).Url;
            }

            return null;
        }

        public IEnumerable<string> GetOtherUrls(UmbracoContext umbracoContext, int id, Uri current)
        {
            return Enumerable.Empty<string>();
        }
    }
}