Иногда сталкиваюсь с такой проблемой «Как проверить UDP порт извне». Бороздя просторы интернета, нашел кое-какой материал.
1. Как проверить TCP порт
Существует я думаю много всяких способов. но вот самые эффективные:
- с помощью telnet
- с помощью nc (netcat)
- с помощью nmap
Ну а теперь разберем по конкретней
С помощью telnet
Если соединение удачно, то увидим такой ответ:
$telnet 11.1.1.11 25
Trying 11.11.11.11...
Connected to mail.domain.com.ua.
Escape character is '^]'.
220 mail.domain.com.ua ESMTP Postfix
Если же неудачное, то такое:
$telnet 11.11.11.11 23
Trying 11.11.11.11...
telnet: connect to address 11.11.11.11: Operation timed out
telnet: Unable to connect to remote host
Иногда в дополнении появляется такое:
telnet: connect to address 11.11.11.11: Operation not permitted
С помощью nc (netcat)
Если соединение удачно, то увидим такой ответ:
$nc -v 11.11.11.11 25
Connection to 11.11.11.11 25 port [tcp/smtp] succeeded!
220 mail.domain.com.ua ESMTP Postfix
Если же неудачное, то такое:
$nc -v 11.11.11.11 23
nc: connect to 11.11.11.11 port 23 (tcp) failed: Operation timed out
С помощью nmap
Если соединение удачно, то увидим такой ответ:
#nmap -p25 11.11.11.11
PORT STATE SERVICE
25/tcp open smtp
Если же неудачное, то такое:
#nmap -p23 11.11.11.11
PORT STATE SERVICE
23/tcp closed telnet
Иногда при сканнировании выводится такое сообщение:
PORT STATE SERVICE
23/tcp filtered telnet
тогда сказать однозначно открыт или закрыт – нельзя.
2. Как проверить UDP порт
Тут есть два способа, с помощью nc (netcat) и с помощью nmap
С помощью nc (netcat)
Если соединение удачно, то увидим такой ответ:
$nc -uv 11.11.11.12 53
Connection to 11.11.11.12 53 port [udp/domain] succeeded!
Если же неудачное, то ничего не выводиться:
$nc -uv 11.1.1.12 50
$
С помощью nmap
Если соединение удачно, то увидим такой ответ:
#nmap -sU -p U:53 11.1.11.12
PORT STATE SERVICE
53/udp open|filtered domain
Если же неудачное, то такое:
#nmap -sU -p U:53 11.1.11.13
PORT STATE SERVICE
53/udp closed domain
Итог
telnet
Преимущества: лёгко и удобно пользоваться, установлена практически на любой ОС, для запуска не требуются права root’a.
Недостатки: нельзя проверять UDP порты
nc (netcat)
Преимущества: лёгко и удобно пользоваться, установлена практически на любой ОС, для запуска не требуются права root’a, есть возможность сканирования UDP-портов
Недостатки: не обнаружено.
nmap
Преимущества: удобно пользоваться, функционал просто радует, есть возможность сканированияUDP-портов
Недостатки: для запуска требуются права root’a, устанавливать приходиться отдельно.
How do I telnet a UDP port in Windows?
Telnet
- Install Telnet if it is not already installed.
- Open the command prompt: Windows: Select Start. Choose Run or Search.
- Enter the command: telnet The Code42 app uses port 443 or 4287 to connect to authority servers and the Code42 cloud. If you are unsure which port to include, test all. Example:
How do I check if port 8443 is open?
Checking Open TCP Ports
- In a Web Browser open URL: http::8873/vab .
- In a Web Browser open URL: http::8443 .
- If TLS/SSL is turned on please repeat the above tests for the appropriate ports (default 8973 & 9443)
How do I telnet to a UDP port?
If you need to connect to udp ports on a certain host, use the netcat command. For udp ports the syntax for netcat is very similar to telnet. The “-u” option connects to udp port.
Does Telnet work on UDP ports?
48.133. Note: Telnet is an application that operates using the TCP protocol. UDP connectivity can not be tested using Telnet.
How do I telnet a udp port?
How do I know if I have TCP or UDP?
Run netstat -an from a Windows command prompt. Download and run TCPView (which also lists UDP) for a GUI view. Run Wireshark.
How do you tell if a port is blocked?
Check for Blocked Port using the Command Prompt
- Type cmd in the search bar.
- Right-click on the Command Prompt and select Run as Administrator.
- In the command prompt, type the following command and hit enter. netsh firewall show state.
- This will display all the blocked and active port configured in the firewall.
Can telnet be used to test UDP ports?
you can’t use telnet to test UDP. telnet is used for testing TCP ports only. you can issue the show crypto ipsec sa if it’s a cisco router.
How to telnet to a port using telnet on Windows 10?
How to telnet to a port using telnet on Windows 10. In Short Answer: To telnet a port you can use the following command: telnet . Example: telnet openport.net 443. Here is a step by step guide:
What is telnet and how to telnet?
Telnet uses a default port for communication, the default telnet port is 23, but you can use telnet on any other port you want. As telnet is a command line interface tool that expects parameters you can set the port you want to connect to. How to telnet a port: First, let’s check if telnet is installed on our system.
What is Telnet port 23 used for?
Telnet is a small application that can be used on your local device to communicate using a textbase, command line, bidirectional interactive terminal. Telnet use port 23 as the default telnet port to send and receive text data over the network. How to telnet to a port using telnet on Windows 10.
What is a simple way in Windows to test if traffic gets through to a specific port on a remote machine?
asked Jul 2, 2009 at 18:01
1
I found a hiddem gem the other day from Microsoft that is designed for testing ports:
Portqry.exe
«Portqry.exe is a command-line utility that you can use to help troubleshoot TCP/IP connectivity issues. Portqry.exe runs on Windows 2000-based computers, on Windows XP-based computers, and on Windows Server 2003-based computers. The utility reports the port status of TCP and UDP ports on a computer that you select. «
answered Jul 2, 2009 at 18:30
Peter MPeter M
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Which version of Windows? For Windows 8/Server 2012 and later, the following works in PowerShell:
Test-NetConnection 128.159.1.1 -Port 80
Some Googling will also turn up alternatives which use the .NET Framework directly (since PowerShell lets you do that) for systems running lower versions of Windows that won’t have Test-NetConnection available.
If you’re not averse to using third-party utilities, Nmap is also a very good friend to have and it works from the command line.
answered Oct 16, 2014 at 6:18
IsziIszi
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Use the telnet command to connect to the server on the specified port, and see if a connection can be established.
Success:
$ telnet my_server 25
220 my_server ESMTP Postfix
Fail:
$ telnet my_server 23632
Connecting To my_server...Could not open connection to the host, on port 23632:
Connect failed
answered Jul 2, 2009 at 18:05
Jørn Schou-RodeJørn Schou-Rode
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Telnet will work for TCP.
Netcat is a better tool for these sorts of things, including UDP, watch out though, some AV softwares consider it an ‘evil hacker tool’
answered Jul 2, 2009 at 18:07
whatsisnamewhatsisname
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Use netcat Windows port:
>nc -zvv www.google.com 80
www.google.com [108.177.96.103] 80 (http) open
sent 0, rcvd 0
>
>nc -zvv www.google.com 888
www.google.com [108.177.96.147] 888 (?): TIMEDOUT
sent 0, rcvd 0: NOTSOCK
>
answered Oct 25, 2016 at 12:48
rustyxrustyx
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the following command will list all ports in use on the machine…
netstat -a
The output contains the protocol, local address, foreign address and current state
Netstat documentation on microsoft.com
answered Jul 11, 2012 at 13:05
BaldyBaldy
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As @iszi’s answer suggested, using the free nmap utility downloadable from nmap.org is a viable option. It could scan for UDP or TCP ports. Example:
nmap -n -P0 -p "80,443" microsoft.com duolingo.com
where
-n never do DNS resolution
-P0 do not ping to test 'up' state
-p this is the list of desired ports
"22,80,443" check in SSH, HTTP and HTTPS in TCP
The port list should be inside quotes in Windows because the comma is interpreted as space in the shell.
Result:
Nmap scan report for microsoft.com (20.53.203.50)
Host is up (0.21s latency).
Other addresses for microsoft.com (not scanned): 20.81.111.85 20.103.85.33 20.84.181.62 20.112.52.29
PORT STATE SERVICE
80/tcp open http
443/tcp open https
Nmap scan report for duolingo.com (184.72.124.184)
Host is up (0.068s latency).
PORT STATE SERVICE
80/tcp open http
443/tcp open https
Nmap done: 2 IP addresses (2 hosts up) scanned in 0.62 seconds
Port 22 is not open on the tested hosts.
Reference: https://nmap.org/book/man.html
answered Oct 27, 2022 at 23:16
FjorFjor
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‘netstat’ is you friend.
answered Jul 2, 2009 at 18:03
2
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To view the TCP/UDP open port state of a remote host, type “portqry.exe –n [hostname/IP]” where [hostname/IP] is replaced with the hostname or IP address of the remote host.
- How do I check if a UDP port is open?
- How do I scan a UDP port?
- How do I know if my port is TCP or UDP?
- How do I find my UDP port number Windows 10?
- Can I Telnet UDP port?
- Do UDP ports listen?
- How many UDP ports are there?
- Why is UDP scan so slow?
- How do I check my ports?
- Does netstat show UDP?
- How do I check if a port is open windows?
- How do I check if a firewall is blocking a port?
How do I check if a UDP port is open?
Follow below steps to check if UDP port is open or closed:
- Open a packet sniffer.
- Send a User Datagram Protocol (UDP) packet.
- After sending the UDP packet, if you receive ‘ICMP port unreachable’ message, then the UDP port is closed.
- If not, then the UDP port is open or something is blocking the ICMP.
How do I scan a UDP port?
Fortunately, Nmap can help inventory UDP ports. UDP scan is activated with the -sU option. It can be combined with a TCP scan type such as SYN scan ( -sS ) to check both protocols during the same run. UDP scan works by sending a UDP packet to every targeted port.
How do I know if my port is TCP or UDP?
Here are a number of methods you can use to determine in real life what transport layer protocol an application is using:
- Run netstat -an from a Windows command prompt.
- Download and run TCPView (which also lists UDP) for a GUI view.
How do I find my UDP port number Windows 10?
Finding an open TCP or UDP port
(For Windows 10, press the Windows button) and type CMD. Now click on Run as Administrator option. When the Command Prompt window opens, type Netstat -ab and press Enter. A list of TCP and UDP ports starts appearing along with the IP address and other details.
Can I Telnet UDP port?
Note: Telnet is an application that operates using the TCP protocol. UDP connectivity can not be tested using Telnet.
Do UDP ports listen?
As mentioned in the comments, UDP is connectionless. Unlike with TCP, it has no concept of «listening», «established», «closed», or anything like that. If a UDP port is open, it appears in the listing; if it’s not open, it doesn’t.
How many UDP ports are there?
Between the protocols User Datagram Protocol (UDP) and Transmission Control Protocol (TCP), there are 65,535 ports available for communication between devices.
Why is UDP scan so slow?
UDP scans are very slow due to the nature of UDP — It’s a stateless protocol that doesn’t acknowledge received packets, so there’s no telling if you’re throwing packets into a black hole, against a firewall, or to a service that just didn’t answer meaningfully.
How do I check my ports?
How to find your port number on Windows
- Type “Cmd” in the search box.
- Open Command Prompt.
- Enter the “netstat -a” command to see your port numbers.
Does netstat show UDP?
netstat displays incoming and outgoing network connections (TCP and UDP), host computer routing table information, and interface statistics.
How do I check if a port is open windows?
On a Windows computer
Press the Windows key + R, then type «cmd.exe» and click OK. Enter «telnet + IP address or hostname + port number» (e.g., telnet www.example.com 1723 or telnet 10.17. xxx. xxx 5000) to run the telnet command in Command Prompt and test the TCP port status.
How do I check if a firewall is blocking a port?
Checking Windows Firewall for blocked ports
- Launch Command Prompt.
- Run netstat -a -n.
- Check to see if the specific port is listed. If it is, then it means that the server is listening on that port.
Most likely your server is a Linux server, if its a windows server then download wireshark and start captureing packets… If your using linux though…
First check if your server is listening on the correct ports:
# netstat -ntlp
# netstat -nulp
-n dont resolve names, u/t udp or tcp, l show listening ports, p show the program pid
You should see your server up and running, if not try to start it up:
sysvinit
/etc/init.d/<service name> stop
/etc/init.d/<service name> start
systemd(using systemctl)
systemctl stop <service>
systemctl start <service>
systemctl status <service>
We will use tcpdump to see if traffic arrives (extremely random note: if your using rsyslog, you can see if traffic arrives by monitoring the syslog file – more on this randomness in another article). We will use netcat (network cat) to send traffic across to udp or tcp ports. Its like the good ol’ telnet test (which telnet can only test tcp, with netcat we can test both)
MONITOR TRAFFIC WITH TCPDUMP (EXAMPLE WITH RSYSLOG)
(How to setup rsyslog: HERE)
ON SERVER (WHERE LISTENING PORT IS AT)
using port 514 as example:
# tcpdump -i eth0 “tcp port 514” -X
or for absolute seq numbers
# tcpdump -i eth0 “tcp port 514” -XS
OR VERY VERBOSE:
# tcpdump -i eth0 “tcp port 514” -vvX
or for absolute seq numbers
# tcpdump -i eth0 “tcp port 514” -vvXS
Legend:
-X show ascii output, vv very verbose, S show absolute seq numbers, -i interface
ON CLIENT
On another pc (client)
TCP:
# nc -vt <ip> <port>
# telnet <ip> <port>
NOTE: telnet works from MS WIN cmd prompt
or
# nc -vu <ip> <port>
Quick Notes on Flags:
then start typing, note on tcpdumps flags
Flag
[S] = Syn
[.] = Ack
[P] = Push
[F] = Fin
UDP traffic intesrting: we dont have an ac for everything and we dont have 3 way connection obviously