指定埠上的遠端 linux 伺服器沒有響應
我有一個遠端 CentOS 6.5 伺服器，它在埠 54321 上執行一個 tomcat 8 Web 伺服器（AKA servlet），我無法從我的電腦訪問它，儘管我正在建立一個成功的 SSH 連接（這就是所有以下日誌/命令範例）以及在埠 80 上退出 Apache Web Sever 時的公共 HTTP 請求。
Tomcat 部署成功，下面是一些日誌輸出：
07-Apr-2015 21:21:10.286 INFO [main] org.apache.coyote.AbstractProtocol.init Initializing ProtocolHandler ["http-nio-54321"] 07-Apr-2015 21:21:10.301 INFO [main] org.apache.tomcat.util.net.NioSelectorPool.getSharedSelector Using a shared selector for servlet write/read 07-Apr-2015 21:21:10.304 INFO [main] org.apache.catalina.startup.Catalina.load Initialization processed in 538 ms 07-Apr-2015 21:21:10.325 INFO [main] org.apache.catalina.core.StandardService.startInternal Starting service Catalina 07-Apr-2015 21:21:10.325 INFO [main] org.apache.catalina.core.StandardEngine.startInternal Starting Servlet Engine: Apache Tomcat/8.0.21 07-Apr-2015 21:21:10.335 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /home/mark/apache-tomcat-8.0.21/webapps/examples 07-Apr-2015 21:21:10.901 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /home/mark/apache-tomcat-8.0.21/webapps/examples has finished in 566 ms 07-Apr-2015 21:21:10.901 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /home/mark/apache-tomcat-8.0.21/webapps/host-manager 07-Apr-2015 21:21:10.923 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /home/mark/apache-tomcat-8.0.21/webapps/host-manager has finished in 22 ms 07-Apr-2015 21:21:10.923 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /home/mark/apache-tomcat-8.0.21/webapps/docs 07-Apr-2015 21:21:10.937 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /home/mark/apache-tomcat-8.0.21/webapps/docs has finished in 14 ms 07-Apr-2015 21:21:10.937 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /home/mark/apache-tomcat-8.0.21/webapps/ROOT 07-Apr-2015 21:21:10.951 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /home/mark/apache-tomcat-8.0.21/webapps/ROOT has finished in 14 ms 07-Apr-2015 21:21:10.951 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory /home/mark/apache-tomcat-8.0.21/webapps/manager 07-Apr-2015 21:21:10.970 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory /home/mark/apache-tomcat-8.0.21/webapps/manager has finished in 19 ms 07-Apr-2015 21:21:10.973 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-54321"] 07-Apr-2015 21:21:10.978 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in 674 ms當我執行時
lsof -i，我可以看到它正在聽：java 32818 mark 49u IPv4 78494638 0t0 TCP *:54321 (LISTEN) java 32818 mark 68u IPv4 78494652 0t0 TCP localhost:mxi (LISTEN)但是當我執行時
nmap localhost，埠沒有出現：Other addresses for localhost (not scanned): 127.0.0.1 Not shown: 993 closed ports PORT STATE SERVICE 22/tcp open ssh 25/tcp open smtp 80/tcp open http 111/tcp open rpcbind 199/tcp open smux 631/tcp open ipp 1311/tcp open rxmon我檢查了
iptables，它是敞開的：Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination這是
system-config-firewall：# Configuration file for system-config-firewall --disabled --service=ssh我也試過
nc -l 54321了，我也遇到了同樣的問題（nc正在聽，但無法通過 找到nmap）。因此，當我嘗試通過瀏覽器遠端連接到 tomcat 時
212.***.***.***:54321，我得到“伺服器沒有響應”（ERR_CONNECTION_TIMED_OUT）。問題出在哪裡？
編輯：
我跑後
nmap -p 54321 localhost看到埠實際上是打開的。那為什麼我無法訪問它？編輯2：
當我使用遠端
nmap測試（不是來自本地主機）時，我以某種方式被過濾：PORT STATE SERVICE 22/tcp open ssh 25/tcp filtered smtp 80/tcp open http 111/tcp filtered rpcbind 199/tcp filtered smux 631/tcp filtered ipp 1311/tcp filtered rxmon埠 -54321 上的 tomcat 也是如此
可能 SELINUX 正在阻止 Tomcat 程序開始偵聽埠 54321。要檢查是否是這種情況，請發出命令
setenforce 0，重新啟動 Tomcat，然後重新嘗試連接。欲了解更多資訊：http ://wiki.centos.org/HowTos/SELinux如果它與 SELINUX 無關，請嘗試連接到發出命令的 localhost
telnet 127.0.0.1 54321。如果 telnet 打開，那麼當來自外部源時，某些東西正在丟棄您的數據包。由於 iptables 已完全禁用，更有可能是外部防火牆（例如：您公司的網關防火牆和/或託管公司的防火牆）阻止了到埠 54321 的流量。為了確定這一點，請
tcpdump -i any -nnn port 54321在您的伺服器上發出命令並嘗試從外部源連接。如果 tcpdump 沒有記錄任何內容，那麼您和您的伺服器（閱讀：網關防火牆）之間的某些東西正在丟棄您的數據包。