Companies Using Application Request Routing

I run the crawler that stores the response headers of every domain we visit, and Application Request Routing is a row that announces itself by default, version number included. A domain counts when a response carries X-Powered-By: ARR/ followed by a version. Our October 2026 crawl puts that at 2,670 domains, 7th of 12 rows, with 1,622 matched to a company. On 16 October 2026 I re-requested every hostname in the clean list, 2,724 of them, and resolved each one's address and CNAME chain to see who runs the proxy.

What the header means

ARR is a module for Microsoft's IIS web server. The IIS.net product page describes rule-based routing, client and host name affinity, load balancing and disk caching, for IIS 7 through IIS 10. Microsoft's download centre still lists ARR 3.0 as version 3.0.5311, free, on a page dated 15 July 2024. The header is on unless someone turns it off: a 2013 post on Microsoft's IIS.net blogs shows the arrResponseHeader setting that removes it. So 2,670 is a floor. The version token is the installed release, and on 16 October 2,206 hostnames reported ARR/3.0 and 130 ARR/2.5.

Sales signal: every domain here has a Windows server with IIS somewhere in its path, and an administrator who left a default setting alone.

Who puts it there

Four operators account for 858 of the 2,724 hostnames. SCHOOLinSITES, a K-12 school website platform, has 420 (15.42%); 226 of them resolve through a hostname literally named arr-connect6.schoolinsites.com, on a Microsoft-network address. One operator's network of near-identical "Airtaxi" city sites adds 200 (7.34%), all behind Cloudflare. Aderian CoreIT, a Swedish IT firm, hosts 124 (4.55%) on a web cluster whose servers say coreit. The platform behind Italy's BCC cooperative banks serves 114 (4.19%) through Imperva, and still on ARR/2.5. Smaller groups follow: Billit's Belgian accounting portals (53), Slovenian municipal sites (51), the UK host Razorblue (49), Microsoft's own Sway (35) and D2L Brightspace course sites (26).

"A school district in Georgia and a cooperative bank in Puglia send the same ARR header for the same reason: their platform's Windows server put it there." - David Thomson, CTO at TechnologyChecker.io

One thing I checked because readers ask: Azure App Service is not the source. Only 5 of the 2,724 hostnames pointed at azurewebsites.net.

Sales signal: for about a third of this list, the buyer of anything server-side is a platform (SCHOOLinSITES, CoreIT, the BCC group's provider), not the school or bank whose name is on the site.

How much of it is current

2,336 of the 2,724 hostnames (85.76%) still sent the header on 16 October 2026, and a separate random draw of 50 gave 41. 103 didn't answer. Two groups have mostly moved off: Brazilian store checkouts on Fbits, where 3 of 65 still send it, and Intermountain Health's sites, where none of 55 do. Error pages are rare, 16 server errors and 30 titled like dead pages. The monthly total went from 1,727 in June to 2,670 in October. Part of that is our side: the set of domains we crawl turns over every month, dead sites out and newly found ones in, and our detection widens. Since tracking began on 16 March 2026, 384 domains dropped the header on at least one hostname, and 33 still send it from another.

Sales signal: an 86% live rate makes this a usable list, but filter out the Fbits and Intermountain rows before you use it.

Who and where

This base is far older than Apache APISIX's. 18.12% of matched companies with a founding year predate 1960, and 51.05% predate 2000, against 9.9% on the APISIX page. Sizes spread out: 40.04% have 1 to 10 employees, 26.67% have 11 to 50 and 16.98% have 51 to 200. The United States has 474 matched companies, 227 of them SCHOOLinSITES schools. Italy has 135, 100 of them BCC banks; Sweden 109, 87 on CoreIT; Brazil 104, 58 of them Fbits checkouts. IT services (5.55%) and banking (4.97%) lead the industries.

Sales signal: school districts, municipalities and cooperative banks buy through procurement and through their platform. Reach them through the platform, or with the public-sector paperwork ready.

The self-run side

Take out the platforms and about half the hostnames remain: Windows shops running ARR on their own servers, usually on one subdomain. That's where the names come from. Samsung's design site, ING's German securities pages, Purolator's freight portal, Persimmon's housebuilding site, Dometic's business site, Milestone Systems, the City of Edmonton's GIS portal, Land Oberösterreich's site and Türk Tuborg's supplier portal all sent the header on 16 October. Six universities on our list, McGill among them, appear only because their D2L Brightspace course sites send it.

Sales signal: a company proxying one subdomain through IIS has a Windows team that owns the box. That team is the buyer for migration, monitoring and managed hosting, and the subdomain tells you which application to talk about.

Overlap and movement

We publish no switching rows for ARR, because none passed our gates. Overlap is thin: 21 domains run an ARR host and an Azure Front Door host today (27 ever), 14 Envoy and 12 Amazon ALB. An answer from Microsoft's external support staff on Microsoft Q&A in July 2023 said ARR may be considered a legacy product, without official confirmation, and named HAProxy and NGINX as options. Our data doesn't show an exit yet.

"ARR isn't being replaced by another row in this table. Where we saw it go, the whole platform changed with it." - David Thomson, CTO at TechnologyChecker.io

Sales signal: pitch the rebuild. Few teams shop for a new reverse proxy while the old IIS box still works.

The stack around it

Across the 2,748 clean domains, IIS shows its own banner on 36.97% and ASP.NET on 12.01%, and SCHOOLinSITES is 420 of the IIS domains. Elsewhere ARR fronts other servers: WordPress runs on 17.94% (124 of those domains on CoreIT's hosting), Next.js on 7.79%, Nginx on 6.8% and Apache on 6.59%. Kestrel, the ASP.NET Core server, shows on 1.56%. Cloudflare sits in front of 29.26%, and jQuery CDN (19.83%) and cdnjs (20.49%) are the common script hosts. DNN (1.97%) and Sitecore (1.49%) are the Windows-native CMSs.

Sales signal: a Windows proxy in front of WordPress or Next.js is a mixed estate with two teams. That's the opening for consolidation and hosting offers.

Key takeaways

• 2,670 domains, 0.77% of Load Balancers & Proxies, 7th of 12, and a floor because the header can be switched off.
• SCHOOLinSITES (15.42%), an Airtaxi site network (7.34%), Aderian CoreIT (4.55%) and the BCC banks' platform (4.19%) send almost a third of it.
• 85.76% still sent the header on 16 October 2026; 2,206 report ARR/3.0.
• 51.05% of matched companies predate 2000: schools, councils and banks.
• No switching rows; the bulk exits we saw were platform changes.

Sales applications

Outreach template: "Your [subdomain] still answers through IIS Application Request Routing 3.0. If that box is on your list to retire, here's how teams like yours move it in a quarter." Use it on the self-run half.

Targeting strategy: drop the SCHOOLinSITES, Airtaxi, CoreIT and BCC rows, then filter for companies with 51 or more staff. That leaves Windows teams with budget.

Competitive angle: you're competing with the rebuild budget, and Envoy or Front Door enter only when that project starts. For the platform rows, talk to the platform.

The full list of 2,670 domains and 1,622 matched companies, with size, country, industry and stack, is on TechnologyChecker.io.