Questions tagged [netcat]
Netcat is a featured networking utility which reads and writes data across network connections, using the TCP/IP protocol.
186
questions
0
votes
0
answers
49
views
Can't see udp packets with nc command, works with tcpdump
I'm trying to capture UDP data using the nc (netcat) command but it doesn't output anything. What options/parameters do I need to pass to the nc command to get the output?
tcpdump does show the UDP ...
1
vote
2
answers
249
views
Netcat successfully sends UDP packet despite all UDP traffic being blocked via Network ACL
I've created an AWS instance in the default VPC and I've blocked all UDP traffic in the Network ACLs. Here's how my outbound rules look:
Rule number
Type
Protocol
Port range
Destination
Allow/Deny
...
- 141
0
votes
1
answer
577
views
How to start netcat listening server in Ansible?
I'm working on larger Ansible playbook. One of the tasks I'd like to use is to do "TCP ping" using netcat. On one of the hosts, I'd like to start a netcat 'server', and then start the '...
- 23
1
vote
1
answer
104
views
IPv6 port scanners hang after scanning a closed port
I am testing nftables firewall rules using two virtual machines, one with the active firewall and one that tries to connect to it.
For example with netcat and no firewall:
nc -6 fe80::9d08:b3e2:47fa:...
- 11
0
votes
0
answers
229
views
How can I print the payload received with ncat?
I'm creating an UDP server with the following command:
ncat -ulk -p 3333 -c "echo asd" -vv
It does receive connections and answers to them correctly, but it doesn't print the UDP payload ...
- 145
0
votes
1
answer
433
views
Netcat UDP server is not sending a response
I'm trying to get OpenBSD netcat to listen to UDP connections on a particular port (3333) and interface (10.42.0.1) and send a fixed response. To achieve this I do:
echo "asd" | nc -k -u -l -...
- 145
0
votes
0
answers
65
views
listen and redirect TCP stream to file with multi client support in the background
is there any tool I can listen on some port and accept any client and redirect the stream to a file. I know it can be done using netcat but it seems netcat cannot keep running in the background.
I did ...
1
vote
0
answers
124
views
xnatd + netcat + ssh = 100% CPU usage
I have a Raspberry PI with a Syncthing Admin-Web-UI binding to localhost:8384.
I can access this UI from my laptop using SSH-tunnel:
$ ssh me@raspberrypi -Llocalhost:8384:localhost:8384
$ chrome http:/...
- 111
0
votes
1
answer
766
views
nc tool not showing any output on busybox for localhost
Any ideas why nc is not showing anything when ran on a busybox based container image?
The problem appears when trying to connect to port on 127.0.0.1/localhost.
/app # nc -v 127.0.0.1 12345
/app # nc -...
- 131
0
votes
1
answer
889
views
traceroute shows stars but netcat reaches the port
I have several (virtual) machines with Centos 7 in the same subnet with several instances of my app running on each of them. I need to test how the apps can reach each other by UDP.
I'm trying to ...
- 223
0
votes
0
answers
22
views
Unable to stream data from Google Cloud to local machine
I'm trying to stream stdout from a VM on Google Cloud Compute Engine to a local machine using nc:
$ mycommand | nc mydomain.net 12345
And listening on the local machine
$ nc -l 12345 | analysis-...
- 1
0
votes
0
answers
307
views
netcat no reaction to syn packet crafted with gopacket
I want to do some experiments with TCP packets. Therefore I am using the gopacket (v1.1.19) to craft packets and send them onto an interface.
I have this code for creating a SYN packet and putting it ...
- 101
0
votes
0
answers
310
views
UDP to Serial port
I look for some solution for connect serial/UART port by UDP connection to another PC.
Now I use socat and have connection , but with lost packages, and slow transfer.
Can I use netcat for this, maybe ...
0
votes
0
answers
97
views
Udp punchhole between two instances behind two different cloud NAT on GCP
Hi I'm trying to achieve UDP punchhole concept between two compute instances (on different networks with no public IP) behind two different cloud NATs for their respective networks. It seems that in ...
1
vote
1
answer
930
views
Scanning a range of ports with Ncat?
I'm aware that Nmap is the obvious choice for this task, however I would still like to know if it's possible to scan a range of ports with Ncat.
I see that I'm able to scan one port, but with a range ...
- 111
0
votes
0
answers
266
views
transfer file at iperf bandwidth/throughput
I need to transfer a file between 2 servers, the output of iperf is:
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[ 3] local X.X.X.X port 58986 ...
- 568
1
vote
0
answers
2k
views
Netcat on MacOS failing with simple commands
I'n trying to follow a tutorial here.
As an example we can say that we need a friend of ours to help us with something on our work system(Windows). To be able to receive a connection from us first ...
1
vote
0
answers
534
views
'socat' not displaying incoming UDP packets, but Wireshark does
The link is an image of a Wireshark dump of an incoming 60-byte Ethernet frame which contains a UDP packet. The packet payload is the single word 'hello' (sorry, I don't have enough rep to paste the ...
- 183
2
votes
1
answer
10k
views
What does `Accept-Encoding: gzip,deflate` mean?
Can someone explain what it means when I see Accept-Encoding: gzip,deflate when listening with ncat?
Does it mean the body is compressed? And if so, how can I decompress it?
$ nc -lnvp 4000
Ncat: ...
- 10.3k
0
votes
1
answer
3k
views
Alternative for "nc -z localhost 3300" for windows [netcat]
I have a sh that is meant to run in linux.
But im using windows, and I must be able to run it in windows
Theres a piece of code that does the following
while ! nc -z localhost 3300; do
echo "...
- 117
0
votes
0
answers
345
views
All traffic on port 5060 gets lost in whole network
I am having issues forwarding port 5060 in my firewall/router to a FreeSWITCH server.
Our firewall/router is an Uniquiti Edge Router X. The server's local IP is 10.0.0.216, the router's 10.0.0.1. ...
0
votes
1
answer
2k
views
netcat-openbsd in RHEL/Centos (RPM)
There are two versions of netcat (nc) utility: netcat-openbsd and GNU netcat. For example, in some distributives like Debian or Arch user could choose which version of the package he/she would like to ...
- 1
3
votes
1
answer
3k
views
Is there a built-in way to proxy SSH through socks5?
I have a Socks5 proxy that uses username/password authentication. I can use it with SSH using NCAT in the ProxyCommand: ssh -o ProxyCommand="ncat --proxy-type socks5 --proxy-auth username:...
- 159
0
votes
1
answer
456
views
Netcat stops listening after Recv-Q fills up
I am running Netcat on an Ubuntu 18.04.3 LTS server, to listen on port 469. This server gets frequent TCP requests from other machines to port 469, which I use to monitor the server for uptime. I ...
- 1
1
vote
1
answer
1k
views
UDP connection i/o timeout while port is reachable
on one server we encountered an issue where all kinds of UDP connections are failing. The same application and tests work on other servers with the same OS and similar setup.
nc -vz -u 83.61.**.** ...
- 203
0
votes
1
answer
624
views
How to check the udp port is accessible in an Ubuntu machine which is protected by a firewall
We were trying to install "Big blue button" in an Ubuntu server with a firewall. For installation, we need these UDP ports ("16384-32768") should be opened in the firewall. But we don't know whether ...
- 57
1
vote
1
answer
2k
views
How to capture UDP traffic so it can be piped to grep
I'm trying to capture UDP traffic which is being sent as StatsD metrics (on port 8125).
The most simple approach I tried is to run nc -ul 8125 which prints the metrics to the terminal...but they are ...
- 113
0
votes
1
answer
211
views
Spawn background process from ncat
How can ncat be used to spawn a process in the background? For example:
ncat -lp 2342 -c "setsid sleep 5 &"
As I understand, setsid and & will make the process run in the background but ncat ...
- 101
3
votes
2
answers
2k
views
Routing TCP packets to a local UDP port
A third party server sends UDP packets to an EC2 instance we've set up and I'm trying to route those packets to my local machine.
The client sends these packets to port 8975
To that effect I first ...
- 153
0
votes
1
answer
1k
views
Simple netcat Responder
Trying to create a simple netcat responder:
The "server" would be:
$ while true; do { ./secret.sh; } | sudo netcat -k -q -1 -l 123; done
secret.sh is:
#!/bin/bash
read line
if [ "$line" == "open" ]...
- 416
1
vote
1
answer
113
views
nc prints (?). What does (?) mean?
When I use nc to test a port as followed, it prints out a result with '(?)' in it. I've looked up the man page and also online but I can't find an answer. Can someone please shed some lights? Thanks.
...
- 165
1
vote
0
answers
343
views
Netcat gives different responses based on IP I give it
I'm currently trying to diagnose why my build of Libreoffice online keeps giving '504 Timed Out' errors on my nginx reverse proxy. I shutdown the entire daemon, hoping to see an error along the lines ...
- 11
2
votes
1
answer
6k
views
Connection refused from localhost to localhost
I started a tcp listener using nc -l 127.0.0.1 900 and then attempted to connect to it using nc 127.0.0.1 900 when I got the connection refused error. The same happens when connecting using telnet. ...
- 25
2
votes
3
answers
2k
views
Why am I only achieving 2.5Gbps over a 10Gbe direct connection between 2 machines?
I have 2 machines directly connected to each other with a 7 foot Cat6a ethernet cable (included in the box of the NIC cards). The PCIe x4 NIC I bought and in both machines is this: https://www.amazon....
- 121
2
votes
3
answers
4k
views
Achieving very fast (300+MB/sec) file transfer on Linux
I'm working with high end hardware, however I'm hitting cpu bottlenecks in all situations when attempting to move large amounts of data.
Specifically, I'm moving large virtual machine image (VHD) ...
- 406
2
votes
1
answer
448
views
SSH tunnel and reverse SSH tunnel at the same time on the same port
I have a computer A, a server B (Azure VM) and a second computer C. I want to connect from A to C through the server B.
Setup:
A: ssh -i location_of_private_key -L 12000:public_IP_of_B:20000 user@...
- 133
2
votes
2
answers
8k
views
netcat host not found when listening
i am trying to connect two hosts using netcat. i have downloaded netcat for windows, but when i run the command nc -L -vv -p 4444, it fails with the error nc: forward host lookup failed: h_errno 11001:...
- 21
0
votes
1
answer
2k
views
Send data recieved by netcat to script
I'm trying to take data I receive over a netcat connection to a script that will send each line to another server via a curl post command.
Heres where I am.
This works: nc -lk 9272 > test.log
...
- 137
0
votes
1
answer
506
views
EHLO returns nothing with postfix initialized working on port 25
So I reinstalled postfix several times because of different issues.
Turns out it starts well and seems to be working on port 25:
I make netstat -nltp | grep 25
tcp 0 0 127.0.0.1:25 ...
- 101
1
vote
1
answer
2k
views
Netcat connection refused apache2 localhost
I have installed webserver (apache) but I can't seem to make netcat connect to it.
$ curl localhost:80 | head
% Total % Received % Xferd Average Speed Time Time Time Current
...
- 143
1
vote
2
answers
9k
views
Connect to an SSH server over an HTTP proxy using plink and netcat
I'm trying to connect to an SSH server from a Windows PC behind a corporate HTTP proxy.
The trick works under Debian using OpenSSH client with ncat from the nmap package, but it does not work under ...
- 11
0
votes
0
answers
77
views
Restore linux partition from remote server
I have a running server with /dev/sda1 partition and a remote server with /dev/sda1 partion also.
I want to clone the partition of running server to remote server.
I want to try this:
On remote ...
- 3
5
votes
1
answer
6k
views
How can I set the source port for an SSH command-line client? [closed]
I am creating a web challenge, and due to a firewall, I need to be able to bind an SSH client source socket to a fixed port to pass its traffic through the firewall.
Is there any way to do this using ...
- 55
0
votes
0
answers
564
views
Link VPS Dedicated IP / Port to Internal Tinc VPN IP Port
After a couple of days research I've completely rewritten my question to make it easier to answer, and hopefully clearer of what I'm looking for.
I have an Ubuntu 18.04 VPS server with a dedicated ...
- 1
0
votes
0
answers
469
views
Can I use netcat for centralized logging?
I have multiple Apache servers and I want to centralize their access logs. I wonder if I can use named pipes and netcat for that, however I am afraid that 2 things may happen:
The central log will be ...
- 1
2
votes
0
answers
1k
views
How to send binary data in netcat to an already established connection?
I can do the following to send binary data in netcat:
echo -e '\x80' | nc host port
But I don't want to do it like this, what I want is to connect to a server:
nc 192.168.1.115 12345
And then send ...
- 21
0
votes
1
answer
15k
views
How to connect netcat from one local computer to another local computer
I want to connect two computers using netcat that are on the different subnets
The problem is when I start Netcat to listen on one computer, I am unable to connect to it from another computer which ...
1
vote
0
answers
336
views
Some clients time out when making a simple TCP proxy with netcat
I have made a simple TCP proxy that rewrtites requests using netcat like so:
nc -q -1 -k -l 8080 < myfifo | sed -u 's/something/something_else/' | nc -q -1 example.com 80 > myfifo
However, ...
user422391
1
vote
1
answer
304
views
How to write and read from the same file using two netcats?
I'd like to use a file as a temporary buffer to connect two netcat processes. I need to use a buffer because data is sent and requested on each end at different intervals. I want to use a file instead ...
- 465
0
votes
1
answer
8k
views
Check if HTTP Methods have been Allowed and Enabled on Localhost
I’m running Apache/2.2.15 (Unix) on a RHEL system. My LAMP is running on localhost.
I want to check if the HTTP methods:
POST
GET
PUT
DELETE
are allowed and enabled.
I’ve read that they can be ...
- 109