Netcat - Httqm's Docs

This situation described here is specific to a misconfiguration on my workstation. This error may happen for other reasons.

nc -v www.myCompany.tld 443

nc: getaddrinfo for host "www.myCompany.tld" port 443: Name or service not known

Am I using an alias ?
type nc
```
nc is aliased to `nc -nvzw5'
```
Where is the Netcat binary ?
which nc
```
/usr/bin/nc
```
Explicitly specifying the absolute path to a binary file circumvents the alias definition.
Let's try executing that binary with our own options and see what happens :
1. options of the alias ;
  /usr/bin/nc -nvzw5 www.myCompany.tld 443
```
nc: getaddrinfo for host "www.myCompany.tld" port 443: Name or service not known
```
  Same error.
2. /usr/bin/nc -v www.myCompany.tld 443
```
Connection to www.myCompany.tld (12.34.56.78) 443 port [tcp/https] succeeded!
```
  No more error . It was caused by the -n flag.

Netcat is known as the "network Swiss-army knife".

nc [flags] destination destinationPort

destinationPort can be :
- a single port number
- a service name
- a range of ports : start-end (both included)

Flag	Usage
-l	listen mode
-n	numeric-only IP addresses, no DNS
-p sourcePort	use the source port sourcePort, subject to privilege restrictions and availability
-q n	after EOF on stdin, wait n seconds, then quit
-s 12.34.56.78	use 12.34.56.78 as the source address
-u	UDP mode (default is TCP)
-v	verbose output (Use this to see error messages)
-w n	wait n seconds before timeout
-z	zero-I/O mode : scan for listening processes without sending any data to them

Scan ports of a host :

Ports list :: nc -vzw5n 12.34.56.78 80 443
Ports range :: nc -z 12.34.56.78 1-1023

Check a remote port is open :

An iptables rule such as :

REJECT	all	--	0.0.0.0/0	0.0.0.0/0	reject-with icmp-host-prohibited

will make this test fail displaying :

No route to host

TCP :

nc -vz ipAddress tcpPort
nc -w 5 -z 12.34.56.78 25 && echo OPEN || echo NOT OPEN

UDP :

nc -vzu host.example.com 160

Test hosts + ports via SSH :

sourceServers='server1 server2 server3'; destinationList='ip.add.ress.1 ip.add.ress.2 ip.add.ress.3'; portList='80 443'; for server in $sourceServers; do for destination in $destinationList; do for port in $portList; do echo -e "\nTESTING FROM '$server' TO '$destination:$port'"; ssh -q $server "nc -nvw3z $destination $port"; done; done; done

Transfer files :

Make the receiver (192.168.3.112) listen on port 8888 :

nc -l -p 8888 > destinationFile
nc -l -p 8888 | pv -W > destinationFile

On the sender side :

nc 192.168.3.112 8888 < sourceFile
cat sourceFile | nc -q 5 192.168.3.112 8888
pv sourceFile | nc 192.168.3.112 8888
cat sourceFile | pv -b | nc 192.168.3.112 8888

Setup a remote shell (source) :

Make the remote host (192.168.3.112) listen on port 8888 :: nc -l -p 8888 -v -e /bin/bash
From the local host :: nc 192.168.3.112 8888

Go through an HTTP proxy (source) :

nc localhost 8080

GET www.google.com/
HEAD www.google.com/
HEAD www.google.com/ HTTP/1.0
HEAD www.google.com/ HTTP/1.1

==> the final 'HTTP/1.x' causes an HTTP 504 (???)






telnet localhost 8080
HEAD http://www.google.com/	+  + 
	==> HTTP/1.1 302 Found

HEAD http://www.google.com/ HTTP/1.0	+  + 
	==> HTTP/1.1 302 Found

HEAD http://www.google.com/ HTTP/1.1	+  + 
	==> HTTP 302

HEAD http://www.google.fr/ HTTP/1.1	+  + 
	==> HTTP 200

Strange output message : nc: timeout cannot be negative

nc -vz 10.27.26.68 22
nc: timeout cannot be negative

nc -vz -w 3 10.27.26.68 22
nc: timeout cannot be negative

nc --version
nc: timeout cannot be negative		

type nc
nc is aliased to `nc -vzw5n'

which nc
/usr/bin/nc

/usr/bin/nc -vzw5n 10.27.26.68 22
nc: timeout cannot be negative

/usr/bin/nc -vzw5 10.27.26.68 22		without -n
nc: connect to 10.27.26.28 port 22 (tcp) timed out: Operation now in progress

/usr/bin/nc -vzw5 -n 10.27.26.68 22	with detached -n
nc: connect to 10.27.26.28 port 22 (tcp) timed out: Operation now in progress

This is not definitely sorted out (weirdness peaks ! ), but at least, there's a means of running nc.

Netcat - the TCP/IP Swiss army knife

Error : nc: getaddrinfo for host "www.myCompany.tld" port 443: Name or service not known

Situation

Details

nc (Netcat)

Usage

Flags

Example