Thank you all for answers.
To make the testing environment as real as possible I bought that Intel Ethernet card. Actually this was pretty good solution, as this ethernet cards cost around €20-25, which is not too bad.
The only problem is, I cannot use this on a laptop on the field - but ok - I do most of the test stuff in the office anyway.
This package might be useful, however changing all T-blocks just for tests and then back might get annoying in a while. However, I might try it anyway :-)