A TCP check attempts to open a connection to your host on a specified port and measures the time until the handshake completes. Unlike ping, it goes through firewall rules and routing policies the same way real application traffic does. This makes it useful for verifying that a port is actually reachable from German networks — not just that a host responds to ICMP.

Common use cases from Germany: checking that a mail server (port 25, 587, 993), game server, VPN endpoint, or custom application port is reachable for German users. Some German ISPs apply outbound filtering on specific ports, particularly port 25 for residential connections. A TCP check from our German nodes lets you verify that none of the ISPs represented in our test pool are blocking the port you depend on.

A failed TCP check from Germany when the port is open from other regions usually means one of three things: the IP is geo-blocked, a firewall or security group is blocking the source ASN, or there is asymmetric routing causing the return path to fail. Cross-referencing against nodes in neighboring countries — Netherlands, France, Switzerland — helps narrow down whether the block is Germany-specific or broader.

Frankfurt is the center of gravity for European internet traffic. DE-CIX Frankfurt is the world's busiest internet exchange by peak throughput, routinely exceeding 20 Tbit/s during peak hours. It connects over 1,000 networks including major carriers, cloud providers, CDNs, and content networks through direct peering — which is why Frankfurt-hosted servers tend to have unusually low latency to destinations across Europe without needing to transit through intermediary cities.

Frankfurt also hosts several other IXPs operating in parallel. KleyReX and LocIX serve networks that prefer smaller, community-oriented peering fabrics. ECIX maintains a Frankfurt presence alongside locations in Hamburg and Düsseldorf. Each of these gives network operators additional peering options beyond DE-CIX, which increases path diversity and resilience at the Frankfurt interconnect level.

Outside Frankfurt, DE-CIX operates regional exchanges in Hamburg, Munich, and Berlin. BCIX (Berlin Commercial Internet Exchange) serves the Berlin carrier ecosystem independently. These regional IXPs matter because not all German traffic routes through Frankfurt — ISPs serving northern Germany often prefer Hamburg peering, and Bavarian providers frequently peer in Munich rather than sending traffic south through Frankfurt first.

Beyond Frankfurt, German hosting infrastructure spreads to Nuremberg, Berlin, Munich, Hamburg, and Düsseldorf. Hetzner (AS24940) runs two of Europe's largest data centers in Nuremberg and Falkenstein. Deutsche Telekom (AS3320) operates the national backbone across all major cities. OVH (AS16276) maintains capacity in Frankfurt and Limburg. Smaller but well-connected providers like GHOSTnet (AS12586), Lumaserv (AS200303), and Packets-Decreaser (AS214243) add diversity at the Frankfurt level. The German hosting market is one of the most competitive in Europe, which means multiple redundant paths exist between most city pairs.

Our probe nodes inside Germany run across several of these providers and cities. Multi-ISP coverage means a result on one node reflects one carrier's routing — not the whole country. Running a check across all German nodes together gives you a realistic picture of what different user segments in Germany actually see, across both Frankfurt-centric and regional routing paths.