- How Can I Read the Route Table?
- How Can I Modify the Route Table?
- How Can I Modify the Route Table to Block Traffic to an Internet Site?
- Recommendations, Caveats, and Other Notes
Recommendations, Caveats, and Other Notes
Modifying the route table the way we suggest does not block unwanted Internet traffic exactly. It redirects IP responses to null addresses disrupting TCP handshakes, thus breaking communication. Newer operating systems and older operating systems with updated patches recover seamlessly from what could be a self-imposed distributed denial-of-service attack. However, older operating systems, particularly ones that are not patched to recover from SYN floods, should not use this method of blocking Internet traffic because it may result in partially connected states. If you have any doubt that your network performance is suffering from hanging connections waiting to close, read our article on the uses of Netstat to help you determine this, patch your OS, and take advantage of this networking trick.
We do not recommend that you delete any of the default routes unless you've researched route tables in greater detail and know exactly what you're doing. However, if you delete a necessary route, rebooting your machine will likely restore that network destination route information to its default values. It's rarely necessary to modify a default route such as the one belonging to the 0.0.0.0 network destination.
Make sure that the IP address you choose to redirect your packets does not belong to a real machine. If it does, the network performance of that machine could potentially degrade as it attempts to handle packets that it has been asked to route.