Reverse IP Lookup

Enter a domain or IP address to see other sites known to be hosted on the same web server. Knowing the other sites sharing a server is useful from both an SEO and web-filtering perspective, particularly for shared-hosting plans.

Background

Every web site is served by a web server identified by an IP address. Since the introduction of the Host header in HTTP/1.1, a single IP can serve many domains, and most do. The vast majority of active domains share an IP with at least one other site, and a large share live on servers running fifty or more neighbors.

Reverse IP lookup answers the question: given this IP or domain, what else lives next to it?The answer is useful in three different contexts — search engine optimization, web filtering, and incident response.

SEO — how search engines treat shared IPs

Search engines weight a page’s rank partly by the number and quality of inbound links. To inflate that signal, a low-effort site operator might spin up dozens of low-content domains all pointing back at a target site. One way search engines push back is to detect when those interlinked domains share an IP or IP range — cheap to host together, easy to flag together — and devalue the links accordingly.

For an ordinary site running a few projects on the same VPS, this isn’t something to worry about. As Matt Cutts, formerly head of Google’s Webspam team, put it:

“If you are an average webmaster and just running a few sites, I wouldn’t worry about them being on the same IP address and I definitely wouldn’t worry about them being on the same server. That’s something that everybody does.”

Web filtering — overblocking

IP-based filtering — the kind used by some corporate firewalls, school filters, and country-level blocks — treats an entire IP as a single unit. If one of the fifty sites on a shared IP is blocked, the other forty-nine go down with it. This is called overblocking, and it’s the most common false-positive failure mode of network-level content filtering.

Reverse IP lookup makes overblocking auditable: if a site is suddenly unreachable, the question “is this an actual block on us, or did a neighbor get blocked and we’re collateral?” becomes answerable in seconds.

What to do about it

If your site is hosted on a shared IP and you want to move off, ask your host for a dedicated IP — specifically a fresh one, not a recycled IP a previous tenant may have gotten blacklisted. Dedicated IPs typically run a small monthly upcharge. For most sites it isn’t worth the cost, but for sites that already have inbound deliverability or filtering problems, it can be the cleanest fix.

About this tool

Results are sourced from Connected’s domain/IP association graph, which records both currently-resolving and historical mappings observed by Connected’s ongoing scan of the open internet. Each row shows the domain, when it was first and last seen on the IP, whether it’s currently active, and where the observation came from (Connected’s own scan, or a bulk-imported source).

Sources