Free tcp ip software for linux

TCP Knocking provides a port knocking implementation.
Often a secure system needs a port open so that only authorized persons can access a particular service and also the service should not exposed to attackers and worms that may use vulnerabilities that exist in the listening server. Port knocking is designed to be used as a complementary service to the existing authentication mechanism. But one of the biggest problems with port knocking is manipulating the firewall with timeouts.
When the correct knock sequence is sent, the firewall is modified for couple of seconds. Having the firewall open automatically for a time period will make any system administrator uncomfortable. TCP knocking attempts to solve the problem by incorporating the knock into the TCP handshake. Tcp knocking is similar to port knocking, but instead sending UDP packets with secret ports, the TCP handshake packets must include secrete codes. It is at least as secure as port knocking and it can be made secure with more hardening.
Modified TCP handshake:
In normal TCP handshake, the client sends the syn packet and chooses a random initial sequence number. The server responds with a packet that has both syn and ack flags set, choosing a random
The modified TCP handshake uses the empty fields in the header. The server does not respond to connection requests without a special code generated along with the syn packet. The server also encrypts the ISN in the ack packet (2) and the final packet of the three-way handshake must have the correct acknowledgment for the servers ISN. The system is further protected from brute-force attacks by closing the connection if the first attempt for the third packet does not have the expected acknowledgment sequence.
Also, rather than use conventional encryption techniques like HMAC for verification, this system uses a file with random numbers as the key. This is because of the limited unused space available in the TCP/IP header which makes HMAC very weak. By using a shared file, the length of the key can be much greater than traditional systems and even though some parts of the key can be revealed by attacks, the server can protect itself from replay attacks.
The handshake:
1) Syn
The syn packet does not use the 32 bit acknowledgment field in the TCP header as it the the first packet to initiate the connection. Further the 16 bit IPID can be used to transmit information. In the current implementation only the 32 bit acknowledgment field is used. Currently the 32 bit ack is derived from a 64 KB file which contains random numbers. The ISN and the source IP address along with the random numbers are used to generate this value.
2) Syn/Ack
The ISN is encrypted using the random numbers from the 64 KB file using the destination IP address as well as a 16 bit random number used as IPID. I do not have code for this part yet.
3) Ack
The client decrypts the syn number from the encrypted syn, the key file, the 16 bit IPID and its own IP address and sends the ack packet. The server closes all connections from the client for couple of minutes if it sends a wrong ack value. Part of the security relies on the fact that the ISN generated by Linux 2.6 is fairly random.
Implementation:
I have implemented only the first part, which is the server expecting secret code along with the first syn packet from the client. Hence it is very possible to brute-force the server. Also the system is designed with the second phase in mind, which is the encrypted Initial Sequence Number in the ack packet and closing the connection if the correct ack is not sent on the first try. I do not have an implementation for that yet. The security will be increased greatly when the second phase is incorporated. Also the ability to detect brute-force attacks can be added to this system.
But the current system can be used for protecting the server from worms and random scanning. The use-case is similar to port knocking but it does not use the ugly system of opening the firewall for a couple of seconds. Vanilla port knocking is susceptible to brute-force attacks as well. Besides, inserting a kernel module to just ssh into your server will increase your mad sysadmin points.
Enhancements:
- TCP knocking with Phase 1 of the protocol was implemented.

libtcp++ is a C++ class library to facilitate the creation of TCP/IP clients and servers. libtcp++ has three classes, TcpClient, TcpServer and TcpIpRuleSet.

TcpServer has build it logging capability peer detection method, and IP-based access control in addition to regular server functionality.

TcpClient supports a user specified timeout on connect(), nice for port/host scanning, and other situations when you may be connecting to a dead host or a firewalled port.

etPan is a console mail user agent based on libEtPan! libEtPan ! is a mail purpose library. Its a library that handles mail at low-level: MAP/NNTP/POP3/SMTP over TCP/IP and SSL/TCP/IP, mbox/MH/maildir, message / MIME parser.
Main features:
- IMAP4rev1 / POP3 / NNTP / mbox / mh / maildir
- virtual folder tree
- multiple folder views and message views
- smart multi-threading
- PGP signing and encryption (using GnuPG as external command)
- S/MIME signing and encryption (using OpenSSL as external command)
- SPAM process (using bogofilter as external command)
- user interface for configuration edition

Empty Clip is a top-down, 2D Action RPG. Empty Clip draws heavily from games such as Crimsonland, Diablo, Alien Swarm, Grand Theft Auto II, and more. There is a campaign, adventure, survival, and primitive deathmatch mode.
Main features:
- 3D hardware accelerated graphics
- Sound and music
- Over 200 different monsters
- Over 400 different items including weapons, armor, and upgrades
- 30+ hours of gameplay
- Travel through mansions, dungeons, forests, caves, cities, skyscrapers, deserts, hell, and alien worlds
- Deathmatch over TCP/IP

external IP shows your current external IP in the browsers statusbar.

External IP is set to check your IP address once every hour.

NBTscan-Ipanto is a command-line tool that scans for NETBIOS devices on a local or remote TCP/IP network.

NBTscan-Ipanto is more powerful than others NETBIOS scanners as it is designed not to flood ARP tables and firewalls. It gives very useful reports, including the username connected on each detected device.

The project is an open source freeware.

Net::TCPwrappers is a Perl interface to tcp_wrappers.

SYNOPSIS

use Net::TCPwrappers qw(RQ_DAEMON RQ_FILE request_init fromhost hosts_access);
...
my $progname = yadd;
while (accept(CLIENT, SERVER)) {
my $req = request_init(RQ_DAEMON, $progname, RQ_FILE, fileno(CLIENT));
fromhost($req);
if (!hosts_access($req)) {
# unauthorized access.
...
}
else {
# service connecting client.
...
}
}

ABSTRACT

Net::TCPwrappers offers perl programmers a convenient interface to the libwrap.a library from tcp_wrappers, Wietse Venemas popular TCP/IP daemon wrapper package. Use it in your perl code to monitor and filter access to TCP-based network services on unix hosts.

Net::TCPwrappers mimics the libwrap.a library fairly closely - the names of the functions and constants are identical, and calling arguments have been altered only slightly to be more perl-like.