01-22-2009
Your router has got a build in firewall.
The firewall is set to allow connections from a pc on the local network to another pc on the local network. ( This is called forwarding ).
By default your ip firewall is set to deny incomming connections to your local network on some ports. the default ports are thos that are used by windows to connect to shared drives.
This is a very important security feature, if you disable these ports or allow traffic on these ports any one on the internet will be able to access your server if the find your public ip address.
Now if you had mail server on your local network and you wanted people to send mail to it on port 25 (SMTP) then you would set a rule in your firewall to allow incomming traffic on port 25 and to forward it to the internal mail server.
So you sepcify what port you allow traffic on and you specify that it can only go to one specific ip address.
Hope this helped
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LEARN ABOUT DEBIAN
dns2tcpc
dns2tcpc(1) General Commands Manual dns2tcpc(1)
NAME
dns2tcpc - A tunneling tool that encapsulate TCP traffic over DNS.
SYNOPSIS
dns2tcpc [ -h ] [ -c ] [ -z domain zone ] [ -d debug_level ] [ -r resource ] [ -k key ] [ -f config_file ] [ -e command ] [ -T request type
] [ -l local_port ] [ server ]
DESCRIPTION
dns2tcpc is a network tool used to encapsulate TCP communications in DNS. When connections are received on a specific port all TCP traffic
is sent to the remote dns2tcpd server and forwarded to a specific host and port. Multiple connections are supported.
dns2tcpc was written for demonstration purposes.
OPTIONS
-h Help Menu
-c Enable DNS compression. When used, be sure that all relay and DNS server support compression and really use it.
-z domain zone
Use this domain as endpoint.
-d debug level
Change debug level. Levels available are 1, 2 or 3.
-r resource
Remote resource to access.
-k key Pre shared key used for authentication (identification).
-f config file
Configuration file to use.
-T request type
Request type to use. Actually only KEY and TXT requests are supported.
-e command
Command to execute, I/O are redirected in the tunnel.
-l local_port
Local port accepting incomming connections (or - for stdin on UNIX systems).
-t connection timeout
Maximum DNS server's answer delay in seconds. A valid delay is between 1 and 240 seconds. Default is 3.
server DNS server to use. The first entry in resolv.conf file will be choosen if the server is not specified.
CONFIGURATION FILES
By default ${HOME}/.dns2tcprc is used if no configuration file is specified. Here is an example :
domain = dns2tcp.hsc.fr
resource = ssltunnel
local_port = 4430
enable_compression = 0
debug_level = 1
key = mykey
# DNS to use
server = ns.hsc.fr
EXAMPLES
dns2tcpc -k mykey -z dns2tcp.hsc.fr mydns
Ask the dns2tcp server to list available resources.
ssh -o 'ProxyCommand dns2tcpc -r ssh -l - -z dns2tcp.hsc.fr -k mykey mydns' myserver
Use dns2tcp as a proxy command with ssh. We try to connect to the ssh resource with the key 'mykey' and the DNS mydns.
dns2tcpc -r socat-resource -e '/bin/bash -i' -k mykey -z dns2tcp.hsc.fr mydns
Use dns2tcp as a reverse shell, the remote shell will appear on the socat-resource.
dns2tcpc -d 1 -f /dev/null -r ssl-tunnel -l 2000 -k mykey -T KEY -z dns2tcp.hsc.fr mydns
Do not use the default configuration file, bind local port 2000 and forward all the traffic on the remote ssl-tunnel resource, use
the first debug level. Use KEY type DNS requests.
AUTHORS
Olivier Dembour <olivier.dembour@hsc.fr>
SEE ALSO
ssltunnel
dns2tcpc(1)