tcp – 503: Service Unavailable

socat is a Multipurpose relay (“is a more complex variant of netcat. It is larger and more flexible and has more options that must be configured for a given task” – Wikipedia):

http://www.dest-unreach.org/socat/

Get it here: socat-1.7.2.0.tar.gz

Examples of use:

socat - TCP4:www.domain.org:80

transfers data between STDIO (-) and a TCP4 connection to port 80 of host http://www.domain.org. This example results in an interactive connection similar to telnet or netcat. The stdin terminal parameters are not changed, so you may close the relay with ^D or abort it with ^C.
socat - SSL:server:4443,cafile=server.crt,cert=client.pem

is an OpenSSL client that tries to establish a secure connection to an SSL server. Option cafile specifies a file that contains trust certificates: we trust the server only when it presents one of these certificates and proofs that it owns the related private key. Otherwise the connection is terminated. With cert a file containing the client certificate and the associated private key is specified. This is required in case the server wishes a client authentication; many Internet servers do not.
The first address (‘-‘) can be replaced by almost any other socat address.
socat - UDP4-DATAGRAM:224.255.0.1:6666,bind=:6666,ip-add-membership=224.255.0.1:eth0

transfers data from stdin to the specified multicast address using UDP. Both local and remote ports are 6666. Tells the interface eth0 to also accept multicast packets of the given group. Multiple hosts on the local network can run this command, so all data sent by any of the hosts will be received by all the other ones. Note that there are many possible reasons for failure, including IP-filters, routing issues, wrong interface selection by the operating system, bridges, or a badly configured switch.