I want to test a toy gateway I wrote. The testing will occur on Linux machines. I would like to do this in the easiest way possible, ideally writing no code and using existing utilities. This boils down to two questions:
Is there an existing utility that can send packets with simple stuff in them(like a string that I supply) to a host through a user-specified gateway, without reconfiguring Linux's network settings? If so, what syntax would I use for the utility?
Is there a simple utility I can run on the receiving end to verify that the correct packet was received? If so, what syntax would I use for the utility?
I don't know about the first, but I don't think it's that hard to modify your routing table:
route add -host 1.2.3.4 gw 5.6.7.8
(replace 1.2.3.4 by your target IP and 5.6.7.8 by the IP of your gateway).
For 2.:
On the target server type netcat -l 1234 and on the client then type netcat 1.2.3.4 1234. (1234 is a "random" port number)(depending on your distribution netcat might be called simple "nc".) If a connection gets established you can just type data on the client or the server machine, press enter and see the data arriving on the other machine.
The easiest would probably be the nc(1). Assuming your gateway IP is 192.168.1.1 and you are using TCP, then on the server, listening on port 8888:
~$ nc -k -l 8888
On the client:
~$ nc 192.168.1.1 8888
your input
...
^C
