I am not a penetration tester but I was listening to some SANS lectures that someone has uploaded to the web. The lecturer said that pen testers and their lawyer should be very careful not to break the law of the countries the packets travel through as it might be illegal to send crafted packages in some countries even for pen testing purposes.
How is even possible to avoid having the packages travel via a certain country?
The Short Answer: You can't
The Long Answer: Once the packet leaves your local network you have no control over how it is routed. It becomes the responsibility of your ISP after that. You can, however, make some reasonable assumptions about where your packets will go, as the entire point of the routing process is to take the 'best' or 'shortest' path. If you need specific data, there are several tools available which provide a graphical representation of a traceroute, such as NeoTrace and GTrace. Personally, I have had success with NeoTrace in the past.
NeoTrace: http://www.networkingfiles.com/neotrace/
