A common way to measure network latency to a remote host is to use thepingapplication. Thepingtool relies on ICMP ECHO request and reply packets to measure the round-trip latency of the remote host. However, in some cases, ICMP traffic may be blocked by a firewall, making thepingapplication useless for hosts behind restricted firewalls. In this case, you will need to rely on layer 3 measurement tools that use TCP/UDP packets, as these layer 3 packets are more likely to bypass common firewall rules.
One such layer 3 measurement tool istcpping. To measure latency,tcppingutilizes the so-calledsemi-open connection technology, based on TCP three-way handshake. That is, it sends a TCP SYN packet to the remote host via the port number (default is 80). If the remote host is listening on that port, it will respond with a TCP ACK packet. Otherwise, it will respond with a TCP RST packet. Either way,tcppingcan measure the round-trip time (RTT) latency of the remote host by timing outgoing SYN packets and incoming ACK (or RST) packets.
tcppingtcppingImplemented as a shell script that responds to external tools to perform and report RTT measurements. Therefore, in order to installtcpping, you first need to install these prerequisites.
tcptracerouteTo install on Ubuntu or Debiantcptraceroute:
$ sudo apt-get install tcptraceroute
To installtcptracerouteon CentOS or RHEL, first set up RepoForge on your system, then run:
$ sudo yum install tcptraceroute
bc使用的另一个工具tcpping是GNUbc，它预装在所有主要的 Linux 发行版上。但是，如果你tcpping在最小 Linux 运行时环境（例如Docker容器、AWS 最小映像 AMI）中运行，则bc可能不会预先安装。在这种情况下，你需要bc自己安装。
在Debian 的 Linux 上安装：
$ sudo apt-get install bc
在 Red Hat 的 Linux 上安装：
$ sudo yum install bc
tcpping安装这些必备工具后，最后继续tcpping从官方源下载。
$ wget http://www.vdberg.org/~richard/tcpping $ cp tcpping /usr/bin $ chmod 755 tcpping
tcpping来衡量延迟要使用 测量网络延迟tcpping，你可以使用以下格式。
tcpping [-d] [-c] [-r sec] [-x count] ipaddress [端口]
-d: 在每个结果之前打印时间戳。-c: 使用分列输出以便于解析。-r：连续探测之间的间隔（以秒为单位）（默认为 1 秒）。-x: 重复 n 次（默认无限制）。[port]: 目标端口（默认为 80）。请注意，你需要 root 权限才能运行，tcpping因为它需要调用特权tcptraceroute命令。
对于任何开放 80 端口的目标 Web 服务器，你可以使用以下方法测量其 RTT 延迟tcpping。
tcpping www.rumenz.com seq 0: tcp response from 42.194.162.109 (42.194.162.109) 33.822 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 1: tcp response from 42.194.162.109 (42.194.162.109) 33.975 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 2: tcp response from 42.194.162.109 (42.194.162.109) 32.010 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 3: tcp response from 42.194.162.109 (42.194.162.109) 32.209 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 4: tcp response from 42.194.162.109 (42.194.162.109) 30.866 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 5: tcp response from 42.194.162.109 (42.194.162.109) 34.866 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 6: tcp response from 42.194.162.109 (42.194.162.109) 32.604 ms traceroute to rumenz.com (42.194.162.109), 255 hops max, 60 byte packets seq 7: tcp response from 42.194.162.109 (42.194.162.109) 30.495 ms
对于任意远程主机，在运行tcpping. 要检查远程 TCP 端口是否打开，你可以使用nc如下命令。
$ nc -vn
-t: 连续 TCPing ，直到使用 Ctrl+C 键停止tcping -t 1.1.1.1 80
-n 5: TCPing 5次后停止tcping -i 5 1.1.1.1 80
-w 0.5: 设置超时时间为 0.5秒（1秒=1000毫秒），单位 秒tcping -w 0.5 1.1.1.1 80
-d:在每行返回信息中加入时间信息tcping -d 1.1.1.1 80
-s: 当 TCPing 测试成功后（在超时时间以内返回 TCPing 延迟数据）自动停止 TCPingtcping -s 1.1.1.1 80
-4: 优先 IPv4（如果一个域名有 IPv4 和 IPv6 解析，那么走 IPv4）tcping -s 1.1.1.1 80
-6:优先 IPv6（如果一个域名有 IPv4 和 IPv6 解析，那么走 IPv6）tcping -6 www.rumenz.com 80
--file: TCPing 将逐行循环遍历文件内的 服务器IP/域名 信息（一行一个，支持端口，例如：1.1.1.1 443）tcping --file rumenz.txt
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