How do I check if a TCP port is open online?

Enter your server's IP address or domain followed by a colon and the port number (e.g. 1.1.1.1:80 or example.com:443) and run a TCP check. The tool attempts a TCP handshake from 50+ global nodes and reports whether each connection succeeded, was refused, or timed out.

What is the difference between a port being refused versus timing out?

A refused connection (TCP RST) means the port is actively closed — the server replied to reject the connection. A timeout means no reply was received at all, which typically indicates a firewall is silently dropping packets before they reach the server or application.

Which TCP ports can I test?

Any valid TCP port from 1 to 65535. Common examples include port 80 (HTTP), 443 (HTTPS), 22 (SSH), 25 (SMTP), 3306 (MySQL), 5432 (PostgreSQL), and 3389 (RDP). No login or special permissions required — the check only verifies whether the TCP handshake completes.

My port is open locally but fails from external nodes — why?

If a port works locally but fails from external nodes, something between the internet and your server is blocking it — commonly a cloud security group, iptables rule, upstream ISP filter, or geoblocking policy. Running the check from multiple regions helps identify whether the block is global or specific to certain countries or ASNs.

check-host.cc:80 的 TCP 端口检测

Name: Check-Host check-host.cc:80 TCP 端口连通性测试
Author: Check-Host

高级设置

显示世界地图

Info Ping HTTP TCP UDP MTR DNS

TCP 通路连通性硬核侦探 (TCP Probe) check-host.cc:80

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探针发哨要塞	握手回馈判决	协商耗费时长 (RTT)	心电图抖动波形 (Jitter)	提取的明文 IP
Albania Tirana
Australia Sydney
Bosnia and Herzegovina Novi Travnik
Bulgaria Sofia
Canada Montreal
Switzerland Bern
Chile Santiago
China Hohhot
Germany Nuernberg
Germany Frankfurt am Main
Germany Frankfurt am Main
Germany Limburg
Germany Frankfurt am Main
Germany Duesseldorf
Denmark Glostrup Municipality
Spain Bilbao
Finland Helsinki
Finland Helsinki
France Gravelines
France Paris
United Kingdom London
Georgia Tbilisi
Greece Athens
Hong Kong Hong Kong
Croatia Zagreb
Hungary Budapest
Indonesia Jakarta
Israel Petach Tikwa
Israel Netanja
India New Delhi
Iceland Reykjavik (Miðborg)
Italy Como
Kuwait Kuwait City
Lithuania Pilaite
Latvia Riga
Moldova Chisinau
Netherlands Amsterdam
Netherlands Amsterdam
Netherlands Amsterdam
Netherlands Amsterdam
Norway Oslo
Poland Warsaw
Romania Bacău
Romania Bucharest
Serbia Belgrade
Russia St Petersburg
Singapore Singapore
Turkey Istanbul
Taiwan Taipei
United States Miami
United States Dallas
United States Kansas City
United States Dallas
South Africa Johannesburg

运用自主分布阵列实施全球 TCP 端口审计扫荡

相较于脆弱且屡屡失陷于各路防火墙屏障的 ICMP (Ping) 回音脉冲，TCP (传输控制协议) 探针探测才是一把能够粗暴捅进服务器内脏，撬开诸如 Web、Mail 等守护进程门禁看门狗的铁撬棍。依靠建立最神圣不容推翻的 TCP 约定礼仪——“三次握手协定 (SYN-SYN ACK-ACK)”——我们在所有防御规则中撕开口子，斩钉截铁地宣告目标机器内在的血肉活力到底还在不在运作。

撕裂藏匿于防火墙后的暗网及粗暴带宽钳制

TCP 侦察返回数据在秒级界标上荒谬的回旋迟滞，常常是不经意间露出的敌情马脚：也许这头巨兽的资源早已饥渴耗竭致死，亦或是前端布罩着阻截洪水猛兽的 DDoS 流量清洗高墙 (强制限速 Rate Limit)，甚至你已经被粗暴的地域版块锁国法案 (Geo-Blocking 地理围栏) 排挤到了黑网单中拒绝准入。

审判冷醋的 “连接遭拒 (Connection Refused)” 与灵异消失的 “死寂超时 (Timeout)”

监测雷达对故障症状的描述字字珠玑。倘若宣判是“连接遭拒 (Connection Refused)”，这表明大门框架完整，但里面的守门人 (应用层服务) 早已卷铺盖走人，或者粗暴地把客房上了锁。而一旦堕入无边深渊般的“超时 (Timeout)”，则暗示你的连接包早就被横跨在半路的幽灵判官——云端入侵防御系统 (IPS) 或者是无影无踪的内网深层过滤筛子——悄然无声地撕碎了。

看破 Anycast 路由迷阵下 BGP 区块负载的分流乱象

对于豪掷千金部署了 CDN 超级节点网络 (譬如 Cloudflare 或 Fastly 之类的 Anycast BGP 大一统路由分发技术) 的霸主而言，借助来自多个不同大洲侦探节点的轮番 TCP 突刺，网络架构总司令便可高枕无虞地审查：各地投石问路的数据请求，究竟有没有完美切中分配给区域最近前哨站的 “靶心 (Edge Proxy)”，抑或是在茫茫网海中迷失了方向。