About ICMP
 

Hi.

I am trying to understand all these kinds of packages. I know C++ but I am not so much familiar with network stuff when I come to packages and layers and so on.

So I thought that I may try to make some different server/klient-kind of programs that would send different packages.

I have done some stuff with iptables before and I noticed that when ICMP in was blocked no one could ping me. Then I have read about different kinds of ICMP. What are these kinds and how can I send/check them? Also how does layers in TCP-packages work and how can I work with them?

Thanks,
MezzyMeat

The main layers to worry about are:

Network layer. For the internet, this is IP, the Internet Protocol. This is an abstraction layer that allows network packets to be sent over any kind of network with a common interface.

Transport Layer. There are two common protocols here, both of which use IP to send information from host to host. UDP is a simple packeted protocol that transmits short packets of information, with a resonable chance that they will get to their destination. TCP is more complex, and provides reliable, streamed connections between the two hosts.

Application layer. These are protocols written for specific applications, such as ICMP. They run over the data link layer protocols; ICMP runs over UDP while HTTP runs over TCP. (There are literally thousands of application layer protocols).

For information relating to specific protocols, look on www.rfc-editor.org where you will find the definitions of all standard Internet protocols, including ICMP.