#DNS2SOCKS DNS to SOCKS or HTTP proxy
DNS2SOCKS is a command line utility running to forward DNS requests to a DNS server via a SOCKS or HTTP tunnel.
I know that this is no new idea, but let me explain why I've coded this: Windows supports using a SOCKS server for Internet connections, but it only uses the SOCKS server for the content and not the DNS requests. I found several articles in the Internet referring this issue. There seem to be tools that do exactly the same thing as DNS2SOCKS, but they either need a scripting interpreter or are not available for downloading anymore.
So I've coded an own tool. It's very(!) simple and doesn't use any sophisticated technology.
To use it, just configure your OS to use the DNS server on the local IP address 127.0.0.1 (IPv4) and/or ::1 (IPv6). On Windows: open the properties of your network adapter. For IPv4 open the properties of "Internet Protocol Version 4 (TCP/IPv4)", select "Use the following DNS server addresses" and enter "127.0.0.1" for the "Preferred DNS server". For IPv6 open the properties of "Internet Protocol Version 6 (TCP/IPv6)", select "Use the following DNS server addresses" and enter "::1" for the "Preferred DNS server".
After that run your SOCKS server (must support SOCKS protocol version 5, for example Tor) or HTTP proxy and start DNS2SOCKS using the correct command line switches (see below). Now all DNS requests of your OS (triggered by any application) run through DNS2SOCKS and your SOCKS server or HTTP proxy.
You can additionally configure Windows to use your SOCKS server for Internet connections (for the content, not DNS). To do this open the "Internet Options" of the control panel, select the tab "Connections" and click on "LAN settings". Check "Use a proxy server for your LAN..." and click on "Advanced". Enter your SOCKS server address and port in the field "Socks". Now Internet Explorer and other tools using these settings get web pages via your SOCKS server. This works with most browsers. However, you should rely on IPv4 for Tor here as (most?) Tor exit servers currently don't support IPv6 (see below). The settings are similar for using a HTTP proxy.
The command line call for DNS2SOCKS has the following format:
DNS2SOCKS [/?] [/t] [/d] [/q] [l[a]:FilePath] [/u:User /p:Password] [Socks5ServIP[:Port]] [DNSServIPorName[:Port]] [ListenIP[:Port]]
/? or any invalid parameter outputs the usage text /t to use a HTTP proxy instead of a SOCKS server (here: Socks5ServIP = HttpProxyIP, no support for /u and /p) /d disables the cache /q disables the text output to the console /l:FilePath creates a new log file "FilePath" /la:FilePath creates a new log file "FilePath" or appends to the file if it already exists /u:User user name if your SOCKS server uses user/password authentication /p:Password password if your SOCKS server uses user/password authentication
The default values for the addresses and ports are (in case you don't specify the command line arguments): Default Socks5ServerIP:Port = 127.0.0.1:9050 Default DNSServerIPorName:Port = 213.73.91.35:53 Default ListenIP:Port = 127.0.0.1:53
So the SOCKS server runs locally on the TCP port 9050 (Tor's default port; attention: for Tor Browser Bundle you must change it to 9150). The used DNS server is 213.73.91.35 (dnscache.berlin.ccc.de). The DNS server must support TCP on port 53 as Tor doesn't support UDP via SOCKS. DNS2SOCKS listens on the UDP port 53 of 127.0.0.1 (only locally) - change this to 0.0.0.0 for listening on all available local IPv4 addresses.
You can launch DNS2SOCKS several times with different settings, for example to listen on IPv6 addresses additionally. To specify an IPv6 address, use the typical format like 1234:5678::1234. To add the port number please embed the IP address in square brackets and add the port number separated by the colon, e.g. [::1]:1024
Hint: In the default configuration Tor only listens on 127.0.0.1 for incoming requests. You can change this in Tor's configuration file using the following line SocksListenAddress 192.168.1.1 In this example it listens on 192.168.1.1 Currently Tor doesn't support IPv6 addresses for listening.
Please note that Tor/Vidalia will output warnings that your application doesn't resolve host names via Tor. This is not true, but Tor can't know this as Tor doesn't recognize the tunneled DNS requests. DNS2SOCKS directly uses the IP address of the DNS server while using SOCKS and also your application will do this as it gets the IP address from DNS2SOCKS. Tor expects getting the host names instead of IP addresses and thus outputs these warnings.
However, instead of an IP address you can also specify the DNS server's name instead of its IP address, e.g. DNS2SOCKS 127.0.0.1 dnscache.berlin.ccc.de ::1 Specifying an IPv6 address for the DNS server is also supported by DNS2SOCKS, but it's not recommended to do this as your current Tor exit server would need to support IPv6, which it typically doesn't. So it's better to specify the DNS server name as the exit server can choose IPv4 or IPv6 automatically this way. Directly specifying an IPv4 address might be a bit faster; currently all Tor exit servers should support this.
As DNS requests running through the SOCKS/HTTP tunnel are very slow, the calling application might time out before it gets the answer - in this case just try it again (press "reload" in the browser).
The output of DNS2SOCKS is very simple. On each new request it outputs the requested name prefixed by the current number of entries in the cache (just an increasing number in case the cache is disabled) and a time stamp. DNS2SOCKS caches DNS requests, so the next time it can serve the answer faster. The cache is a very simple list. There is no sophisticated hash algorithm or something like that for the cache and DNS2SOCKS doesn't really interpret the DNS requests and answers - it just forwards them.
DNS2SOCKS runs as long as you don't manually stop it. You can also run several instances of DNS2SOCKS at the same time when using different local ports or IPv4 and IPv6 at the same time, e.g. use a batch file and Window's Start command to do this.
If you think that DNS2SOCKS is not the right tool for you, but you want to route all network traffic of a specific Windows application through a SOCKS tunnel, you might want to try my tool InjectSOCKS.
Now about some technical details: DNS2SOCKS listens on the local UDP and TCP port you specify. In case it gets a request it first searches the cache for an identical request. In case of a cache miss or expiration of the entry, the tool creates a new thread for resolving the request. The new thread opens a TCP connection to the SOCKS server and forwards the DNS request. This time the DNS request always runs on TCP as Tor currently doesn't support UDP via SOCKS. So the DNS server must support TCP. When the thread finally gets the answer, it forwards it via UDP or TCP to the requesting client and stores it in the cache. DNS2SOCKS supports user/password authentication (method 0x02) for SOCKS.
I've tried to comment the source code as good as possible and you can compile it using Visual C++ 2010 Express Edition (or any other edition). I've also tested it on Knoppix and Damn Small Linux and compiled it via
gcc -pthread -Wall -O2 -o DNS2SOCKS DNS2SOCKS.c
or (static compile)
gcc -lpthread -Wall -O2 -Wl,-static -static -static-libgcc -s -o dns2socks DNS2SOCKS.c
It should also run on other *nix variants; maybe with tiny modifications.
Have fun using this software!
ghostmaker
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