即NetCat簡寫，在網路工具中有“瑞士軍刀”美譽，其有Windows和Linux的版本。因為它短小精悍（1.84版本也不過25k，舊版本或縮減版甚至更小）、功能實用，被設計為一個簡單、可靠的網路工具，可通過TCP或UDP協議傳輸讀寫資料。同時，它還是一個網路應用Debug分析器，因為它可以根據需要建立各種不同型別的網路連線。NetCat 官方地址：http://netcat.sourceforge.net/
功能說明：功能強大的網路工具
語 法：nc [-hlnruz][-g<閘道器...>][-G<指向器數目>][-i<延遲秒數>][-o<輸出檔案>][-p<通訊埠>][-s<來源位址>][-v...][-w<超時秒數>][主機名稱][通訊埠...]
參 數：
-g <閘道器> 設定路由器躍程通訊閘道器，最多可設定8個。
-G <指向器數目> 設定來源路由指向器，其數值為4的倍數。
-h 線上幫助。
-i <延遲秒數> 設定時間間隔，以便傳送資訊及掃描通訊埠。
-l 使用監聽模式，管控傳入的資料。
-n 直接使用IP地址，而不通過域名伺服器。
-o <輸出檔案> 指定檔名稱，把往來傳輸的資料以16進位制字碼傾倒成該檔案儲存。
-p <通訊埠> 設定本地主機使用的通訊埠。
-r 亂數指定本地與遠端主機的通訊埠。
-s <來源位址> 設定本地主機送出資料包的IP地址。
-u 使用UDP傳輸協議。
-v 顯示指令執行過程。
-w <超時秒數> 設定等待連線的時間。
-z 使用0輸入/輸出模式，只在掃描通訊埠時使用。1.埠掃描
[root@rusky2 ~]# nc -v 192.168.2.100 -z 11162-11170
Connection to 192.168.2.100 11162 port [tcp/suncacao-jmxmp] succeeded!
Connection to 192.168.2.100 11163 port [tcp/suncacao-rmi] succeeded!
Connection to 192.168.2.100 11164 port [tcp/suncacao-csa] succeeded!
nc: connect to 192.168.2.100 port 11165 (tcp) failed: Connection refused
nc: connect to 192.168.2.100 port 11166 (tcp) failed: Connection refused
nc: connect to 192.168.2.100 port 11167 (tcp) failed: Connection refused
nc: connect to 192.168.2.100 port 11168 (tcp) failed: Connection refused
nc: connect to 192.168.2.100 port 11169 (tcp) failed: Connection refused
nc: connect to 192.168.2.100 port 11170 (tcp) failed: Connection refused
不加-v引數，則只顯示已開啟的埠
[root@rusky2 ~]# nc 192.168.2.100 -z 11162-11170
Connection to 192.168.2.100 11162 port [tcp/suncacao-jmxmp] succeeded!
Connection to 192.168.2.100 11163 port [tcp/suncacao-rmi] succeeded!
Connection to 192.168.2.100 11164 port [tcp/suncacao-csa] succeeded!
2、簡單聊天工具
[root@rusky ~]# nc -l 1234 #rusky開始埠1234
hello rusky
hello rusky2
[root@rusky2 ~]# nc 192.168.2.100 1234 #rusk2連線埠1234
hello rusky
hello rusky2 [root@rusky ~]# netstat -an | grep 1234
tcp 0 0 0.0.0.0:1234 0.0.0.0:* LISTEN
tcp 0 0 192.168.2.100:1234 192.168.2.200:58039 ESTABLISHED
3.。。。。。。。。
[root@YncmIAM-ESP-a ~]# man 1 nc
NC(1) BSD General Commands Manual NC(1)
NAME
nc - arbitrary TCP and UDP connections and listens
SYNOPSIS
nc [-46DdhklnrStUuvz] [-i interval] [-p source_port] [-s source_ip_address] [-T ToS] [-w timeout]
[-X proxy_protocol] [-x proxy_address[:port]] [hostname] [port[s]]
DESCRIPTION
The nc (or netcat) utility is used for just about anything under the sun involving TCP or UDP. It can
open TCP connections, send UDP packets, listen on arbitrary TCP and UDP ports, do port scanning, and
deal with both IPv4 and IPv6. Unlike telnet(1), nc scripts nicely, and separates error messages onto
standard error instead of sending them to standard output, as telnet(1) does with some.
Common uses include:
??¤ simple TCP proxies
??¤ shell-script based HTTP clients and servers
??¤ network daemon testing
??¤ a SOCKS or HTTP ProxyCommand for ssh(1)
??¤ and much, much more
The options are as follows:
-4 Forces nc to use IPv4 addresses only.
-6 Forces nc to use IPv6 addresses only.
-D Enable debugging on the socket.
-d Do not attempt to read from stdin.
-h Prints out nc help.
-i interval
Specifies a delay time interval between lines of text sent and received. Also causes a delay
time between connections to multiple ports.
-k Forces nc to stay listening for another connection after its current connection is completed.
It is an error to use this option without the -l option.
-l Used to specify that nc should listen for an incoming connection rather than initiate a con-
nection to a remote host. It is an error to use this option in conjunction with the -p, -s,
or -z options. Additionally, any timeouts specified with the -w option are ignored.
-n Do not do any DNS or service lookups on any specified addresses, hostnames or ports.
-p source_port
Specifies the source port nc should use, subject to privilege restrictions and availability.
It is an error to use this option in conjunction with the -l option.
-r Specifies that source and/or destination ports should be chosen randomly instead of sequen-
tially within a range or in the order that the system assigns them.
-S Enables the RFC 2385 TCP MD5 signature option.
-s source_ip_address
Specifies the IP of the interface which is used to send the packets. It is an error to use
this option in conjunction with the -l option.
-T ToS Specifies IP Type of Service (ToS) for the connection. Valid values are the tokens
?°lowdelay?±, ?°throughput?±, ?°reliability?±, or an 8-bit hexadecimal value preceded by ?°0x?±.
-t Causes nc to send RFC 854 DON?ˉT and WON?ˉT responses to RFC 854 DO and WILL requests. This
makes it possible to use nc to script telnet sessions.
-U Specifies to use Unix Domain Sockets.
-u Use UDP instead of the default option of TCP.
-v Have nc give more verbose output.
-w timeout
If a connection and stdin are idle for more than timeout seconds, then the connection is
silently closed. The -w flag has no effect on the -l option, i.e. nc will listen forever for
a connection, with or without the -w flag. The default is no timeout.
-X proxy_version
Requests that nc should use the specified protocol when talking to the proxy server. Sup-
ported protocols are ?°4?± (SOCKS v.4), ?°5?± (SOCKS v.5) and ?°connect?± (HTTPS proxy). If the
protocol is not specified, SOCKS version 5 is used.
-x proxy_address[:port]
Requests that nc should connect to hostname using a proxy at proxy_address and port. If port
is not specified, the well-known port for the proxy protocol is used (1080 for SOCKS, 3128 for
HTTPS).
-z Specifies that nc should just scan for listening daemons, without sending any data to them.
It is an error to use this option in conjunction with the -l option.
hostname can be a numerical IP address or a symbolic hostname (unless the -n option is given). In
general, a hostname must be specified, unless the -l option is given (in which case the local host is
used).
port[s] can be single integers or ranges. Ranges are in the form nn-mm. In general, a destination
port must be specified, unless the -U option is given (in which case a socket must be specified).
CLIENT/SERVER MODEL
It is quite simple to build a very basic client/server model using nc. On one console, start nc lis-
tening on a specific port for a connection. For example:
$ nc -l 1234
nc is now listening on port 1234 for a connection. On a second console (or a second machine), connect
to the machine and port being listened on:
$ nc 127.0.0.1 1234
There should now be a connection between the ports. Anything typed at the second console will be con-
catenated to the first, and vice-versa. After the connection has been set up, nc does not really care
which side is being used as a ??server?ˉ and which side is being used as a ??client?ˉ. The connection may
be terminated using an EOF (??^D?ˉ).
DATA TRANSFER
The example in the previous section can be expanded to build a basic data transfer model. Any infor-
mation input into one end of the connection will be output to the other end, and input and output can
be easily captured in order to emulate file transfer.
Start by using nc to listen on a specific port, with output captured into a file:
$ nc -l 1234 > filename.out
Using a second machine, connect to the listening nc process, feeding it the file which is to be trans-
ferred:
$ nc host.example.com 1234 < filename.in
After the file has been transferred, the connection will close automatically.
TALKING TO SERVERS
It is sometimes useful to talk to servers ?°by hand?± rather than through a user interface. It can aid
in troubleshooting, when it might be necessary to verify what data a server is sending in response to
commands issued by the client. For example, to retrieve the home page of a web site:
$ echo -n "GET / HTTP/1.0\r\n\r\n" | nc host.example.com 80
Note that this also displays the headers sent by the web server. They can be filtered, using a tool
such as sed(1), if necessary.
More complicated examples can be built up when the user knows the format of requests required by the
server. As another example, an email may be submitted to an SMTP server using:
$ nc localhost 25 << EOF
HELO host.example.com
MAIL FROM: <user@host.example.com>
RCPT TO: <user2@host.example.com>
DATA
Body of email.
.
QUIT
EOF
PORT SCANNING
It may be useful to know which ports are open and running services on a target machine. The -z flag
can be used to tell nc to report open ports, rather than initiate a connection. For example:
$ nc -z host.example.com 20-30
Connection to host.example.com 22 port [tcp/ssh] succeeded!
Connection to host.example.com 25 port [tcp/smtp] succeeded!
The port range was specified to limit the search to ports 20 - 30.
Alternatively, it might be useful to know which server software is running, and which versions. This
information is often contained within the greeting banners. In order to retrieve these, it is neces-
sary to first make a connection, and then break the connection when the banner has been retrieved.
This can be accomplished by specifying a small timeout with the -w flag, or perhaps by issuing a
"QUIT" command to the server:
$ echo "QUIT" | nc host.example.com 20-30
SSH-1.99-OpenSSH_3.6.1p2
Protocol mismatch.
220 host.example.com IMS SMTP Receiver Version 0.84 Ready
EXAMPLES
Open a TCP connection to port 42 of host.example.com, using port 31337 as the source port, with a
timeout of 5 seconds:
$ nc -p 31337 -w 5 host.example.com 42
Open a UDP connection to port 53 of host.example.com:
$ nc -u host.example.com 53
Open a TCP connection to port 42 of host.example.com using 10.1.2.3 as the IP for the local end of the
connection:
$ nc -s 10.1.2.3 host.example.com 42
Create and listen on a Unix Domain Socket:
$ nc -lU /var/tmp/dsocket
Connect to port 42 of host.example.com via an HTTP proxy at 10.2.3.4, port 8080. This example could
also be used by ssh(1); see the ProxyCommand directive in ssh_config(5) for more information.
$ nc -x10.2.3.4:8080 -Xconnect host.example.com 42
SEE ALSO
cat(1), ssh(1)
AUTHORS
Original implementation by *Hobbit* ?′hobbit@avian.org?μ.
Rewritten with IPv6 support by Eric Jackson ?′ericj@monkey.org?μ.
CAVEATS
UDP port scans will always succeed (i.e. report the port as open), rendering the -uz combination of
flags relatively useless.
BSD