1NCAT(1) Ncat Reference Guide NCAT(1)
2
6 ncat - Concatenate and redirect sockets
7
9 ncat [OPTIONS...] [hostname] [port]
10
12 Ncat is a feature-packed networking utility which reads and writes data
13 across networks from the command line. Ncat was written for the Nmap
14 Project and is the culmination of the currently splintered family of
15 Netcat incarnations. It is designed to be a reliable back-end tool to
16 instantly provide network connectivity to other applications and users.
17 Ncat will not only work with IPv4 and IPv6 but provides the user with a
18 virtually limitless number of potential uses.
19 Among Ncat's vast number of features there is the ability to chain
21 Ncats together; redirection of TCP, UDP, and SCTP ports to other sites;
22 SSL support; and proxy connections via SOCKS4, SOCKS5 or HTTP proxies
23 (with optional proxy authentication as well). Some general principles
24 apply to most applications and thus give you the capability of
25 instantly adding networking support to software that would normally
26 never support it.
27
29 Ncat 7.80 ( https://nmap.org/ncat )
30 Usage: ncat [options] [hostname] [port]
31 Options taking a time assume seconds. Append 'ms' for milliseconds,
33 's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
34 -4 Use IPv4 only
35 -6 Use IPv6 only
36 -U, --unixsock Use Unix domain sockets only
37 --vsock Use vsock sockets only
38 -C, --crlf Use CRLF for EOL sequence
39 -c, --sh-exec <command> Executes the given command via /bin/sh
40 -e, --exec <command> Executes the given command
41 --lua-exec <filename> Executes the given Lua script
42 -g hop1[,hop2,...] Loose source routing hop points (8 max)
43 -G <n> Loose source routing hop pointer (4, 8, 12, ...)
44 -m, --max-conns <n> Maximum <n> simultaneous connections
45 -h, --help Display this help screen
46 -d, --delay <time> Wait between read/writes
47 -o, --output <filename> Dump session data to a file
48 -x, --hex-dump <filename> Dump session data as hex to a file
49 -i, --idle-timeout <time> Idle read/write timeout
50 -p, --source-port port Specify source port to use
51 -s, --source addr Specify source address to use (doesn't affect -l)
52 -l, --listen Bind and listen for incoming connections
53 -k, --keep-open Accept multiple connections in listen mode
54 -n, --nodns Do not resolve hostnames via DNS
55 -t, --telnet Answer Telnet negotiations
56 -u, --udp Use UDP instead of default TCP
57 --sctp Use SCTP instead of default TCP
58 -v, --verbose Set verbosity level (can be used several times)
59 -w, --wait <time> Connect timeout
60 -z Zero-I/O mode, report connection status only
61 --append-output Append rather than clobber specified output files
62 --send-only Only send data, ignoring received; quit on EOF
63 --recv-only Only receive data, never send anything
64 --no-shutdown Continue half-duplex when receiving EOF on stdin
65 --allow Allow only given hosts to connect to Ncat
66 --allowfile A file of hosts allowed to connect to Ncat
67 --deny Deny given hosts from connecting to Ncat
68 --denyfile A file of hosts denied from connecting to Ncat
69 --broker Enable Ncat's connection brokering mode
70 --chat Start a simple Ncat chat server
71 --proxy <addr[:port]> Specify address of host to proxy through
72 --proxy-type <type> Specify proxy type ("http", "socks4", "socks5")
73 --proxy-auth <auth> Authenticate with HTTP or SOCKS proxy server
74 --proxy-dns <type> Specify where to resolve proxy destination
75 --ssl Connect or listen with SSL
76 --ssl-cert Specify SSL certificate file (PEM) for listening
77 --ssl-key Specify SSL private key (PEM) for listening
78 --ssl-verify Verify trust and domain name of certificates
79 --ssl-trustfile PEM file containing trusted SSL certificates
80 --ssl-ciphers Cipherlist containing SSL ciphers to use
81 --ssl-alpn ALPN protocol list to use.
82 --version Display Ncat's version information and exit
83 See the ncat(1) manpage for full options, descriptions and usage examples
85
88 Ncat operates in one of two primary modes: connect mode and listen
89 mode. Other modes, such as the HTTP proxy server, act as special cases
90 of these two. In connect mode, Ncat works as a client. In listen mode
91 it is a server.
92 In connect mode, the hostname and port arguments tell what to connect
94 to. hostname is required, and may be a hostname or IP address. If port
95 is supplied, it must be a decimal port number. If omitted, it defaults
96 to 31337.
97 In listen mode, hostname and port control the address the server will
99 bind to. Both arguments are optional in listen mode. If hostname is
100 omitted, it defaults to listening on all available addresses over IPv4
101 and IPv6. If port is omitted, it defaults to 31337.
102
104 -4 (IPv4 only)
105 Force the use of IPv4 only.
106 -6 (IPv6 only)
108 Force the use of IPv6 only.
109 -U, --unixsock (Use Unix domain sockets)
111 Use Unix domain sockets rather than network sockets. This option
112 may be used on its own for stream sockets, or combined with --udp
113 for datagram sockets. A description of -U mode is in the section
114 called “UNIX DOMAIN SOCKETS”.
115 -u, --udp (Use UDP)
117 Use UDP for the connection (the default is TCP).
118 --sctp (Use SCTP)
120 Use SCTP for the connection (the default is TCP). SCTP support is
121 implemented in TCP-compatible mode.
122 --vsock (Use AF_VSOCK sockets)
124 Use AF_VSOCK sockets rather than the default TCP sockets (Linux
125 only). This option may be used on its own for stream sockets or
126 combined with --udp for datagram sockets. A description of --vsock
127 mode is in the section called “AF_VSOCK SOCKETS”.
128
130 -g hop1[,hop2,...] (Loose source routing)
131 Sets hops for IPv4 loose source routing. You can use -g once with a
132 comma-separated list of hops, use -g multiple times with single
133 hops to build the list, or combine the two. Hops can be given as IP
134 addresses or hostnames.
135 -G ptr (Set source routing pointer)
137 Sets the IPv4 source route “pointer” for use with -g. The argument
138 must be a multiple of 4 and no more than 28. Not all operating
139 systems support setting this pointer to anything other than four.
140 -p port, --source-port port (Specify source port)
142 Set the port number for Ncat to bind to.
143 -s host, --source host (Specify source address)
145 Set the address for Ncat to bind to.
146
148 See the section called “ACCESS CONTROL OPTIONS” for information on
149 limiting the hosts that may connect to the listening Ncat process.
150 -l, --listen (Listen for connections)
152 Listen for connections rather than connecting to a remote machine
153 -m numconns, --max-conns numconns (Specify maximum number of
155 connections)
156 The maximum number of simultaneous connections accepted by an Ncat
157 instance. 100 is the default (60 on Windows).
158 -k, --keep-open (Accept multiple connections)
160 Normally a listening server accepts only one connection and then
161 quits when the connection is closed. This option makes it accept
162 multiple simultaneous connections and wait for more connections
163 after they have all been closed. It must be combined with --listen.
164 In this mode there is no way for Ncat to know when its network
165 input is finished, so it will keep running until interrupted. This
166 also means that it will never close its output stream, so any
167 program reading from Ncat and looking for end-of-file will also
168 hang.
169 --broker (Connection brokering)
171 Allow multiple parties to connect to a centralised Ncat server and
172 communicate with each other. Ncat can broker communication between
173 systems that are behind a NAT or otherwise unable to directly
174 connect. This option is used in conjunction with --listen, which
175 causes the --listen port to have broker mode enabled.
176 --chat (Ad-hoc “chat server”)
178 The --chat option enables chat mode, intended for the exchange of
179 text between several users. In chat mode, connection brokering is
180 turned on. Ncat prefixes each message received with an ID before
181 relaying it to the other connections. The ID is unique for each
182 connected client. This helps distinguish who sent what.
183 Additionally, non-printing characters such as control characters
184 are escaped to keep them from doing damage to a terminal.
185
187 --ssl (Use SSL)
188 In connect mode, this option transparently negotiates an SSL
189 session with an SSL server to securely encrypt the connection. This
190 is particularly handy for talking to SSL enabled HTTP servers, etc.
191 In server mode, this option listens for incoming SSL connections,
193 rather than plain untunneled traffic.
194 In UDP connect mode, this option enables Datagram TLS (DTLS). This
196 is not supported in server mode.
197 --ssl-verify (Verify server certificates)
199 In client mode, --ssl-verify is like --ssl except that it also
200 requires verification of the server certificate. Ncat comes with a
201 default set of trusted certificates in the file ca-bundle.crt.
202 Some operating systems provide a default list of trusted
203 certificates; these will also be used if available. Use
204 --ssl-trustfile to give a custom list. Use -v one or more times to
205 get details about verification failures. Ncat does not check for
206 revoked certificates.
207 This option has no effect in server mode.
209 --ssl-cert certfile.pem (Specify SSL certificate)
211 This option gives the location of a PEM-encoded certificate files
212 used to authenticate the server (in listen mode) or the client (in
213 connect mode). Use it in combination with --ssl-key.
214 --ssl-key keyfile.pem (Specify SSL private key)
216 This option gives the location of the PEM-encoded private key file
217 that goes with the certificate named with --ssl-cert.
218 --ssl-trustfile cert.pem (List trusted certificates)
220 This option sets a list of certificates that are trusted for
221 purposes of certificate verification. It has no effect unless
222 combined with --ssl-verify. The argument to this option is the name
223 of a PEM file containing trusted certificates. Typically, the file
224 will contain certificates of certification authorities, though it
225 may also contain server certificates directly. When this option is
226 used, Ncat does not use its default certificates.
227 --ssl-ciphers cipherlist (Specify SSL ciphersuites)
229 This option sets the list of ciphersuites that Ncat will use when
230 connecting to servers or when accepting SSL connections from
231 clients. The syntax is described in the OpenSSL ciphers(1) man
232 page, and defaults to
233 ALL:!aNULL:!eNULL:!LOW:!EXP:!RC4:!MD5:@STRENGTH
234 --ssl-alpn ALPN list (Specify ALPN protocol list)
236 This option allows you to specify a comma-separated list of
237 protocols to send via the Application-Layer Protocol Negotiation
238 (ALPN) TLS extension. Not supported by all versions of OpenSSL.
239
241 --proxy host[:port] (Specify proxy address)
242 Requests proxying through host:port, using the protocol specified
243 by --proxy-type.
244 If no port is specified, the proxy protocol's well-known port is
246 used (1080 for SOCKS and 3128 for HTTP). When specifying an IPv6
247 HTTP proxy server using the IP address rather than the hostname,
248 the square-bracket notation (for example [2001:db8::1]:8080) MUST
249 be used to separate the port from the IPv6 address. If the proxy
250 requires authentication, use --proxy-auth.
251 --proxy-type proto (Specify proxy protocol)
253 In connect mode, this option requests the protocol proto to connect
254 through the proxy host specified by --proxy. In listen mode, this
255 option has Ncat act as a proxy server using the specified protocol.
256 The currently available protocols in connect mode are http
258 (CONNECT), socks4 (SOCKSv4), and socks5 (SOCKSv5). The only server
259 currently supported is http. If this option is not used, the
260 default protocol is http.
261 --proxy-auth user[:pass] (Specify proxy credentials)
263 In connect mode, gives the credentials that will be used to connect
264 to the proxy server. In listen mode, gives the credentials that
265 will be required of connecting clients. For use with --proxy-type
266 http or --proxy-type socks5, the form should be username:password.
267 For --proxy-type socks4, it should be a username only.
268 --proxy-dns type (Specify where to resolve proxy destination)
270 In connect mode, it provides control over whether proxy destination
271 hostnames are resolved by the remote proxy server or locally, by
272 Ncat itself. Possible values for type are:
273 local - Hostnames are resolved locally on the Ncat host. Ncat exits
275 with error if the hostname cannot be resolved.
276 remote - Hostnames are passed directly onto the remote proxy
278 server. This is the default behavior.
279 both - Hostname resolution is first attempted on the Ncat host.
281 Unresolvable hostnames are passed onto the remote proxy server.
282 none - Hostname resolution is completely disabled. Only a literal
284 IPv4 or IPv6 address can be used as the proxy destination.
285 Local hostname resolution generally respects IP version specified
287 with options -4 or -6, except for SOCKS4, which is incompatible
288 with IPv6.
289
291 -e command, --exec command (Execute command)
292 Execute the specified command after a connection has been
293 established. The command must be specified as a full pathname. All
294 input from the remote client will be sent to the application and
295 responses sent back to the remote client over the socket, thus
296 making your command-line application interactive over a socket.
297 Combined with --keep-open, Ncat will handle multiple simultaneous
298 connections to your specified port/application like inetd. Ncat
299 will only accept a maximum, definable, number of simultaneous
300 connections controlled by the -m option. By default this is set to
301 100 (60 on Windows).
302 -c command, --sh-exec command (Execute command via sh)
304 Same as -e, except it tries to execute the command via /bin/sh.
305 This means you don't have to specify the full path for the command,
306 and shell facilities like environment variables are available.
307 --lua-exec file (Execute a .lua script)
309 Runs the specified file as a Lua script after a connection has been
310 established, using a built-in interpreter. Both the script's
311 standard input and the standard output are redirected to the
312 connection data streams.
313 All exec options add the following variables to the child's
315 environment:
316 NCAT_REMOTE_ADDR, NCAT_REMOTE_PORT
318 The IP address and port number of the remote host. In connect mode,
319 it's the target's address; in listen mode, it's the client's
320 address.
321 NCAT_LOCAL_ADDR, NCAT_LOCAL_PORT
323 The IP address and port number of the local end of the connection.
324 NCAT_PROTO
326 The protocol in use: one of TCP, UDP, and SCTP.
327
329 --allow host[,host,...] (Allow connections)
330 The list of hosts specified will be the only hosts allowed to
331 connect to the Ncat process. All other connection attempts will be
332 disconnected. In case of a conflict between --allow and --deny,
333 --allow takes precedence. Host specifications follow the same
334 syntax used by Nmap.
335 --allowfile file (Allow connections from file)
337 This has the same functionality as --allow, except that the allowed
338 hosts are provided in a new-line delimited allow file, rather than
339 directly on the command line.
340 --deny host[,host,...] (Deny connections)
342 Issue Ncat with a list of hosts that will not be allowed to connect
343 to the listening Ncat process. Specified hosts will have their
344 session silently terminated if they try to connect. In case of a
345 conflict between --allow and --deny, --allow takes precedence. Host
346 specifications follow the same syntax used by Nmap.
347 --denyfile file (Deny connections from file)
349 This is the same functionality as --deny, except that excluded
350 hosts are provided in a new-line delimited deny file, rather than
351 directly on the command line.
352
354 These options accept a time parameter. This is specified in seconds by
355 default, though you can append ms, s, m, or h to the value to specify
356 milliseconds, seconds, minutes, or hours.
357 -d time, --delay time (Specify line delay)
359 Set the delay interval for lines sent. This effectively limits the
360 number of lines that Ncat will send in the specified period. This
361 may be useful for low-bandwidth sites, or have other uses such as
362 coping with annoying iptables --limit options.
363 -i time, --idle-timeout time (Specify idle timeout)
365 Set a fixed timeout for idle connections. If the idle timeout is
366 reached, the connection is terminated.
367 -w time, --wait time (Specify connect timeout)
369 Set a fixed timeout for connection attempts.
370
372 -o file, --output file (Save session data)
373 Dump session data to a file
374 -x file, --hex-dump file (Save session data in hex)
376 Dump session data in hex to a file.
377 --append-output (Append output)
379 Issue Ncat with --append-ouput along with -o and/or -x and it will
380 append the resulted output rather than truncating the specified
381 output files.
382 -v, --verbose (Be verbose)
384 Issue Ncat with -v and it will be verbose and display all kinds of
385 useful connection based information. Use more than once (-vv,
386 -vvv...) for greater verbosity.
387
389 -C, --crlf (Use CRLF as EOL)
390 This option tells Ncat to convert LF line endings to CRLF when
391 taking input from standard input. This is useful for talking to
392 some stringent servers directly from a terminal in one of the many
393 common plain-text protocols that use CRLF for end-of-line.
394 -h, --help (Help screen)
396 Displays a short help screen with common options and parameters,
397 and then exits.
398 --recv-only (Only receive data)
400 If this option is passed, Ncat will only receive data and will not
401 try to send anything.
402 --send-only (Only send data)
404 If this option is passed, then Ncat will only send data and will
405 ignore anything received. This option also causes Ncat to close the
406 network connection and terminate after EOF is received on standard
407 input.
408 --no-shutdown (Do not shutdown into half-duplex mode)
410 If this option is passed, Ncat will not invoke shutdown on a socket
411 after seeing EOF on stdin. This is provided for
412 backward-compatibility with OpenBSD netcat, which exhibits this
413 behavior when executed with its '-d' option.
414 -n, --nodns (Do not resolve hostnames)
416 Completely disable hostname resolution across all Ncat options,
417 such as the destination, source address, source routing hops, and
418 the proxy. All addresses must be specified numerically. (Note that
419 resolution of proxy destinations is controlled separately via
420 option --proxy-dns.)
421 -t, --telnet (Answer Telnet negotiations)
423 Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
424 possible to script Telnet sessions with Ncat.
425 --version (Display version)
427 Displays the Ncat version number and exits.
428
430 The -U option (same as --unixsock) causes Ncat to use Unix domain
431 sockets rather than network sockets. Unix domain sockets exist as an
432 entry in the filesystem. You must give the name of a socket to connect
433 to or to listen on. For example, to make a connection,
434 ncat -U ~/unixsock
436 To listen on a socket:
438 ncat -l -U ~/unixsock
440 Listen mode will create the socket if it doesn't exist. The socket will
442 continue to exist after the program ends.
443 Both stream and datagram domain sockets are supported. Use -U on its
445 own for stream sockets, or combine it with --udp for datagram sockets.
446 Datagram sockets require a source socket to connect from. By default, a
447 source socket with a random filename will be created as needed, and
448 deleted when the program ends. Use the --source with a path to use a
449 source socket with a specific name.
450
452 The --vsock option causes Ncat to use AF_VSOCK sockets rather than
453 network sockets. A CID must be given instead of a hostname or IP
454 address. For example, to make a connection to the host,
455 ncat --vsock 2 1234
457 To listen on a socket:
459 ncat -l --vsock 1234
461 Both stream and datagram domain sockets are supported, but socket type
463 availability depends on the hypervisor. Use --vsock on its own for
464 stream sockets, or combine it with --udp for datagram sockets.
465
467 Connect to example.org on TCP port 8080.
468 ncat example.org 8080
469 Listen for connections on TCP port 8080.
471 ncat -l 8080
472 Redirect TCP port 8080 on the local machine to host on port 80.
474 ncat --sh-exec "ncat example.org 80" -l 8080 --keep-open
475 Bind to TCP port 8081 and attach /bin/bash for the world to access
477 freely.
478 ncat --exec "/bin/bash" -l 8081 --keep-open
479 Bind a shell to TCP port 8081, limit access to hosts on a local
481 network, and limit the maximum number of simultaneous connections to 3.
482 ncat --exec "/bin/bash" --max-conns 3 --allow 192.168.0.0/24 -l
483 8081 --keep-open
484 Connect to smtphost:25 through a SOCKS4 server on port 1080.
486 ncat --proxy socks4host --proxy-type socks4 --proxy-auth joe
487 smtphost 25
488 Connect to smtphost:25 through a SOCKS5 server on port 1080.
490 ncat --proxy socks5host --proxy-type socks5 --proxy-auth joe:secret
491 smtphost 25
492 Create an HTTP proxy server on localhost port 8888.
494 ncat -l --proxy-type http localhost 8888
495 Send a file over TCP port 9899 from host2 (client) to host1 (server).
497 HOST1$ ncat -l 9899 > outputfile
498 HOST2$ ncat HOST1 9899 < inputfile
500 Transfer in the other direction, turning Ncat into a “one file” server.
502 HOST1$ ncat -l 9899 < inputfile
503 HOST2$ ncat HOST1 9899 > outputfile
505
507 The exit code reflects whether a connection was made and completed
508 successfully. 0 means there was no error. 1 means there was a network
509 error of some kind, for example “Connection refused” or “Connection
510 reset”. 2 is reserved for all other errors, like an invalid option or a
511 nonexistent file.
512
514 Like its authors, Ncat isn't perfect. But you can help make it better
515 by sending bug reports or even writing patches. If Ncat doesn't behave
516 the way you expect, first upgrade to the latest version available from
517 https://nmap.org. If the problem persists, do some research to
518 determine whether it has already been discovered and addressed. Try
519 Googling the error message or browsing the nmap-dev archives at
520 http://seclists.org/.
521 Read this full manual page as well. If nothing comes of this, mail a
523 bug report to <dev@nmap.org>. Please include everything you have
524 learned about the problem, as well as what version of Ncat you are
525 running and what operating system version it is running on. Problem
526 reports and Ncat usage questions sent to dev@nmap.org are far more
527 likely to be answered than those sent to Fyodor directly.
528 Code patches to fix bugs are even better than bug reports. Basic
530 instructions for creating patch files with your changes are available
531 at https://svn.nmap.org/nmap/HACKING. Patches may be sent to nmap-dev
532 (recommended) or to Fyodor directly.
533
535 • Chris Gibson <chris@linuxops.net>
536 • Kris Katterjohn <katterjohn@gmail.com>
538 • Mixter <mixter@gmail.com>
540 • Fyodor <fyodor@nmap.org> (http://insecure.org)
542 The original Netcat was written by *Hobbit* <hobbit@avian.org>. While
544 Ncat isn't built on any code from the “traditional” Netcat (or any
545 other implementation), Ncat is most definitely based on Netcat in
546 spirit and functionality.
547
549 Ncat Copyright and Licensing
550 Ncat is (C) 2005–2018 Insecure.Com LLC. It is distributed as free and
551 open source software under the same license terms as our Nmap software.
552 Precise terms and further details are available from
553 https://nmap.org/man/man-legal.html.
554 Creative Commons License for this Ncat Guide
556 This Ncat Reference Guide is (C) 2005–2018 Insecure.Com LLC. It is
557 hereby placed under version 3.0 of the Creative Commons Attribution
558 License[1]. This allows you redistribute and modify the work as you
559 desire, as long as you credit the original source. Alternatively, you
560 may choose to treat this document as falling under the same license as
561 Ncap itself (discussed previously).
562 Source Code Availability and Community Contributions
564 Source is provided to this software because we believe users have a
565 right to know exactly what a program is going to do before they run it.
566 This also allows you to audit the software for security holes (none
567 have been found so far).
568 Source code also allows you to port Nmap (which includes Ncat) to new
570 platforms, fix bugs, and add new features. You are highly encouraged to
571 send your changes to <dev@nmap.org> for possible incorporation into the
572 main distribution. By sending these changes to Fyodor or one of the
573 Insecure.Org development mailing lists, it is assumed that you are
574 offering the Nmap Project (Insecure.Com LLC) the unlimited,
575 non-exclusive right to reuse, modify, and relicense the code. Nmap will
576 always be available open source, but this is important because the
577 inability to relicense code has caused devastating problems for other
578 Free Software projects (such as KDE and NASM). We also occasionally
579 relicense the code to third parties as discussed in the Nmap man page.
580 If you wish to specify special license conditions of your
581 contributions, just say so when you send them.
582 No Warranty
584 This program is distributed in the hope that it will be useful, but
585 WITHOUT ANY WARRANTY; without even the implied warranty of
586 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
587 General Public License v2.0 for more details at
588 http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file
589 included with Nmap.
590 Inappropriate Usage
592 Ncat should never be installed with special privileges (e.g. suid
593 root). That would open up a major security vulnerability as other
594 users on the system (or attackers) could use it for privilege
595 escalation.
596 Third-Party Software
598 This product includes software developed by the Apache Software
599 Foundation[2]. A modified version of the Libpcap portable packet
600 capture library[3] is distributed along with Ncat. The Windows version
601 of Ncat utilized the Libpcap-derived Npcap library[4] instead. Certain
602 raw networking functions use the Libdnet[5] networking library, which
603 was written by Dug Song. A modified version is distributed with Ncat.
604 Ncat can optionally link with the OpenSSL cryptography toolkit[6] for
605 SSL version detection support. All of the third-party software
606 described in this paragraph is freely redistributable under BSD-style
607 software licenses.
608
610 1. Creative Commons Attribution License
611 http://creativecommons.org/licenses/by/3.0/
612 2. Apache Software Foundation
614 http://www.apache.org
615 3. Libpcap portable packet capture library
617 http://www.tcpdump.org
618 4. Npcap library
620 https://npcap.org
621 5. Libdnet
623 http://libdnet.sourceforge.net
624 6. OpenSSL cryptography toolkit
626 http://www.openssl.org
627Ncat 08/12/2019 NCAT(1)