TCP checks from our Istanbul node (AS44620) attempt a SYN-ACK handshake to your host on the specified port and measure connection time. This verifies port-level reachability from Turkish network infrastructure and is useful for confirming that application ports are accessible for Turkish users. TCP checks bypass ICMP handling and reflect actual firewall and routing behaviour on the path from Netlen's Istanbul data center to your target.

Expected TCP handshake times from Istanbul: to Frankfurt-region targets ~44–50 ms, to Amsterdam ~52–60 ms, to London ~58–66 ms, to Moscow ~52–60 ms, to US East Coast ~122–135 ms. A TCP check completing faster than these baselines — say, under 10 ms to a European host — confirms the target is Anycast-routed with a local Istanbul edge, such as a Cloudflare or Akamai-fronted service.

A failed TCP check from Turkey on a port that is reachable from Western Europe can indicate geo-restriction, ASN-based firewall rules, or Turkish national-level filtering. Netlen (AS44620) is a legitimate Turkish commercial ISP and its address space should not trigger standard commercial WAF rules. If a TCP block is observed specifically from our Istanbul node, comparing against our Israel and German nodes will help determine whether the block is Turkey-specific or affects a broader Middle East / non-EU IP range.

Istanbul is Turkey's internet hub and one of the most strategically positioned network cities in the world. It sits on the geographic boundary between Europe and Asia, and cable routes between the two continents physically pass through or near the city. Terrestrial fiber crossing the Bosphorus links European and Asian network segments, making Istanbul a natural transit point for traffic moving between Central Europe, the Middle East, and South and Central Asia. DE-CIX opened an Istanbul platform specifically because of this geographic leverage, giving carriers a neutral peering point at the Europe-Asia crossroads.

The Turkish internet backbone is anchored by Turk Telekom (AS9121), which operates the dominant fixed-line infrastructure and holds significant transit market share. TTNET is its internet subsidiary. Vodafone Turkey (AS15897), Turkcell (AS47331), and a range of commercial ISPs and hosting providers compete below the Turk Telekom tier. Our probe node runs on Netlen Internet (AS44620), a Turkish colocation and ISP with data center infrastructure in Istanbul. Netlen operates within the Istanbul carrier ecosystem and peers at TurkIX and DE-CIX Istanbul.

DE-CIX Istanbul provides a neutral peering fabric that sits alongside TurkIX and ISTIX. The presence of a DE-CIX platform in Istanbul has improved peering efficiency for international carriers that already peer at DE-CIX Frankfurt or Madrid — they can extend the same peering policies to Istanbul without a separate bilateral arrangement. This matters for latency: a CDN with Istanbul peering can serve Turkish users directly rather than routing through Frankfurt and back, saving 80–100 ms in round-trip time.

Istanbul to Frankfurt runs approximately 43–50 ms on well-routed paths. Istanbul to Moscow is around 50–60 ms. Istanbul to Cairo runs approximately 38–45 ms. Istanbul to Dubai is roughly 50–65 ms. These figures reflect Istanbul's physical position between Europe and the Middle East — the city has shorter RTTs to Moscow and Cairo than most Western European capitals do. Istanbul to New York is approximately 120–135 ms via trans-Atlantic routing through European transit.

Our probe node in Istanbul (AS44620, Netlen Internet) is located in Netlen's data center in Istanbul. Results from this node reflect connectivity through a mid-tier Turkish commercial ISP with local peering at Istanbul exchanges. For targets that have CDN or hosting presence in Turkey, results will be significantly faster than for targets served only from Western Europe. The node is useful for diagnosing whether a service is properly peered for Turkish users or whether all Turkish traffic is routing the long way through Frankfurt.