How to solve the problem of ping being successful but the port being unavailable in Linux

Description of port availability detection when ping is successful but the port is not accessible

Introduction to Port Availability Detection Tool

Different operating systems use different tools to detect port availability.

Introduction to port availability detection tools in Linux environment

Traceroute is a network testing tool pre-installed in almost all Linux distributions, used to track the path that Internet Protocol (IP) packets take when they are transmitted to the destination address. You can use the traceroute tool to detect port availability.

Traceroute detects the connectivity of the corresponding port on the entire link from the packet source to the target server by sending TCP packets to the target port.

The common usage of traceroute port availability detection is as follows:

traceroute [-n] -T -p <destination port number> Host

Example

[root@centos~]# traceroute -n -T -p 22 223.5.5.5
traceroute to 223.5.5.5 (223.5.5.5), 30 hops max, 60 byte packets
 1 58.96.171.249 0.431 ms 0.538 ms 0.702 ms
 2 10.88.16.29 0.997 ms 1.030 ms 10.88.16.21 1.309 ms
 3 58.96.160.246 0.393 ms 0.390 ms 58.96.160.250 0.423 ms
 4 63.218.56.237 1.110 ms 202.123.74.122 0.440 ms 0.440 ms
 5 63.223.15.90 1.744 ms 63.218.56.237 1.076 ms 1.232 ms
 6 63.223.15.158 1.832 ms 63.223.15.90 1.663 ms 63.223.15.74 1.616 ms
 7 202.97.122.113 2.776 ms 63.223.15.154 1.585 ms 1.606 ms
 8 * * 202.97.122.113 2.537 ms
 9 202.97.61.237 6.856 ms * *
10 * * *
11 * * *
12 * * 119.147.220.222 8.738 ms
13 119.147.220.230 8.248 ms 8.231 ms *
14 * 42.120.242.230 32.305 ms 42.120.242.226 29.877 ms
15 42.120.242.234 11.950 ms 42.120.242.222 23.853 ms 42.120.242.218 29.831 ms
16 42.120.253.2 11.007 ms 42.120.242.234 13.615 ms 42.120.253.2 11.956 ms
17 42.120.253.14 21.578 ms 42.120.253.2 13.236 ms *
18 * * 223.5.5.5 12.070 ms !X

Parameter Description

-n Use IP addresses directly instead of host names (disables DNS lookup).

-T Probe via TCP.

-p detects the target port number.

Host Target server domain name or IP.

For more information about traceroute, you can refer to the man page.

Introduction to port availability detection tools in Windows environment

In Windows environment, you can use tracetcp to detect port availability.

tracetcp also performs link detection by sending TCP packets to analyze whether any intermediate nodes in the link have blocked the target port.

Download and install

The use of tracetcp depends on the WinPcap library, so you need to download it from the official website.

Click here to go to the official website to download the latest version of tracetcp. Alternatively, you can download the attached v1.0.2 of tracetcp (which may not be the latest version).

Unzip the downloaded tracetcp related files directly to the C:\Windows directory. (If you unzip to a non-system directory, you need to manually modify the system environment variables to ensure that the command can be called directly)

How to use

Double-click to open the tracetcp application. Common uses of tracetcp are as follows:

tracetcp <target server domain name or IP>:<port number to be detected>

Example

C:\ >tracetcp www.aliyun.com:80
Tracing route to 140.205.63.8 on port 80
Over a maximum of 30 hops.
1 3 ms 4 ms 3 ms 30.9.176.1
2 13 ms 3 ms 4 ms 10.64.200.33
3 3 ms 3 ms 2 ms 10.64.1.1
4 4 ms 3 ms 3 ms 42.120.74.4
5 5 ms 4 ms 7 ms 42.120.253.233
6 6 ms 5 ms 7 ms 42.120.247.97
7 8 ms 8 ms 8 ms 42.120.247.97
8 10 ms 10 ms 8 ms 123.56.34.246
9 9 ms 9 ms 11 ms 42.120.243.117
10 * * * Request timed out.
11 Destination Reached in 8 ms. Connection established to 140.205.63.8
Trace Complete.

You can use tracetcp -? to obtain and view more tracetcp parameter descriptions.

Port availability detection steps

Typically, you can:

According to the foregoing description, use the corresponding tool to detect the availability of the target port of the target address.

Check and analyze the detection results to identify abnormal nodes.

Obtain the corresponding node's operator and network through IP address query websites such as ip.taobao.com.

Or you can submit a work order and Alibaba Cloud will report the problem to the relevant operator for you.

Brief description of link test result analysis

Abnormal node determination method: If the relevant port is blocked at a certain hop, no data will be returned at the subsequent hops. Based on this, abnormal nodes can be identified.

Example 1

C:\>tracetcp www.aliyun.com:135
Tracing route to 115.239.210.27 on port 135
Over a maximum of 30 hops.
1 3 ms 3 ms 3 ms 30.9.176.1
2 4 ms 3 ms 3 ms 10.64.200.33
3 3 ms 3 ms 3 ms 10.64.1.1
4 * * * Request timed out.
5 * * * Request timed out.
6 * * * Request timed out.
7 * * * Request timed out.
8 * * * Request timed out.
9 * * * Request timed out.
10 * * * Request timed out.
11 * * * Request timed out.
12 * * * Request timed out.
13 * * * Request timed out.
14 * * * Request timed out.
15 * * * Request timed out.
16 * * * Request timed out.
17 * * * Request timed out.
18 * * * Request timed out.
19 * * * Request timed out.
20 * * * Request timed out.
21 * * * Request timed out.
22 * * * Request timed out.
23 * * * Request timed out.
24 * * * Request timed out.
25 * * * Request timed out.
26 * * * Request timed out.
27 * * * Request timed out.
28 * * * Request timed out.
29 * * * Request timed out.
30 * * * Request timed out.
Trace Complete.

In the above detection data, the target port does not return any data after the third hop. Indicates that the corresponding port is blocked on this node.

Example conclusion: Because the node is an intranet IP, it may be caused by local network security policies. You need to contact the local network administrator for further investigation and analysis.

Example 2

[root@mycentos ~]# traceroute -T -p 135 www.baidu.com
traceroute to www.baidu.com (111.13.100.92), 30 hops max, 60 byte packets
 1 * * *
 2 192.168.17.20 (192.168.17.20) 4.115 ms 4.397 ms 4.679 ms
 3 111.1.20.41 (111.1.20.41) 901.921 ms 902.762 ms 902.338 ms
 4 111.1.34.197 (111.1.34.197) 2.187 ms 1.392 ms 2.266 ms
 5 * * *
 6 221.183.19.169 (221.183.19.169) 1.688 ms 1.465 ms 1.475 ms
 7 221.183.11.105 (221.183.11.105) 27.729 ms 27.708 ms 27.636 ms
 8 * * *
 9 * * *
10 111.13.98.249 (111.13.98.249) 28.922 ms 111.13.98.253 (111.13.98.253) 29.030 ms 28.916 ms
11 111.13.108.22 (111.13.108.22) 29.169 ms 28.893 ms 111.13.108.33 (111.13.108.33) 30.986 ms
12 * * *
13 * * *
14 * * *
15 * * *
16 * * *
17 * * *
18 * * *
19 * * *
20 * * *
twenty one * * *
twenty two * * *
twenty three * * *
twenty four * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *

In the above detection data, the target port does not return any data after the 11th hop. Indicates that the corresponding port is blocked on this node.

Example conclusion: Because the node belongs to Beijing Mobile after query, you need to check it yourself or submit a work order for further investigation and analysis.