Linux SOCK_RAW和SOCK_STREAM有什么区别？

Question

I've been studying networking with c code and cryptography lately and upon pondering random questions I stumbled across a block of code that's used for packet sniffing and I had a question on the actual socket that gets used in the function recvfrom() . The socket gets initialized through the following sock function rawSock = socket(AF_INET, SOCK_RAW, 0) .

I understand that SOCK_STREAM and SOCK_RAW are macros that represent an integer; but the question isn't about the values, it's about the results.

When would I use SOCK_STREAM over SOCK_RAW and vice versa?

I understand basic client and server communications using SOCK_STREAM . I'm working with C and in Linux

Answer 1

Read the man page .

For the prototype

int socket(int domain, int type, int protocol);

The types can be

   SOCK_STREAM     Provides sequenced, reliable, two-way, connection-
                   based byte streams.  An out-of-band data transmission
                   mechanism may be supported.

or

   SOCK_RAW        Provides raw network protocol access.

In one line, SOCK_STREAM is for connection oriented sockets, where the underlying OS creates and manages the headers for L4 (TCP), L3 and L2. OTOH SOCK_RAW provides more fine-grained control over header and packet construction, where the user has to construct and supply the headers and can also manage the contents.

To elaborate:

Sockets of type SOCK_STREAM are full-duplex byte streams. They do not preserve record boundaries. A stream socket must be in a connected state before any data may be sent or received on it. A connection to another socket is created with a connect(2) call. Once connected, data may be transferred using read(2) and write(2) calls or some variant of the send(2) and recv(2) calls. When a session has been completed a close(2) may be performed. Out-of-band data may also be transmitted as described in send(2) and received as described in recv(2).

and

SOCK_RAW sockets allow sending of datagrams to correspondents named in sendto(2) calls. Datagrams are generally received with recvfrom(2), which returns the next datagram along with the address of its sender.