IPPROTO_IP与IPPROTO_TCP / IPPROTO_UDP [英] IPPROTO_IP vs IPPROTO_TCP/IPPROTO_UDP

问题描述

我在查找有关 socket 的第三个参数的这些设置之间区别的文档时遇到了一些问题。我知道TCP和UDP及其差异，以及IP是堆栈上的一层（向下？）...我的UDP代码似乎工作相同，无论我将其设置为 IPPROTO_IP 或 IPPROTO_UDP 。

I'm having some trouble finding documentation on what the distinction between these settings for the third argument to socket is. I know about TCP and UDP and their differences and also that IP is one layer up (down?) on the stack... My UDP code seems to work the same whether I set it to IPPROTO_IP or IPPROTO_UDP.

推荐答案

Linux上 socket（）的文档分为各种联机帮助页包括 ip（7），指定你必须使用 0 或 IPPROTO_UDP 用于UDP， 0 或 IPPROTO_TCP 用于TCP。当您使用 0 （恰好是 IPPROTO_IP 的值时，UDP用于 SOCK_DGRAM 和TCP用于 SOCK_STREAM 。

Documentation for socket() on Linux is split between various manpages including ip(7) that specifies that you have to use 0 or IPPROTO_UDP for UDP and 0 or IPPROTO_TCP for TCP. When you use 0, which happens to be the value of IPPROTO_IP, UDP is used for SOCK_DGRAM and TCP is used for SOCK_STREAM.

在我看来，干净的方式是创建UDP或TCP IPv4套接字对象如下：

In my opinion the clean way to create a UDP or a TCP IPv4 socket object is as follows:

int sock_udp = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
int sock_tcp = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

原因是显性通常比隐式更好。在这种特殊情况下，使用 0 或更糟 IPPROTO_IP 第三个参数不会获得任何收益。

The reason is that it is generally better to be explicit than implicit. In this specific case using 0 or worse IPPROTO_IP for the third argument doesn't gain you anything.

还可以设想使用可以同时执行流和数据报的协议，例如 sctp 。通过始终指定 socktype 和协议，您可以避免任何歧义。

Also imagine using a protocol that can do both streams and datagrams like sctp. By always specifying both socktype and protocol you are safe from any ambiguity.

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