sockets - 跟踪路由中的SO_DEBUG和SO_DONTROUTE

Question

谁能解释SO_DEBUG和SO_DONTROUTE之间的区别。这是我的理解

SO_DONTROUTE

            Enable / disable routing bypass for outgoing message

            Routing takes place only when it goes to out of subnet.

            This tell that do not route, directly connect to the destination instead of routing

            SO_DONTROUTE refers to the local routing

            But default it is zero

            Do not route send directly to the connected network

            If the host is not on a directly-attached network
    an error is returned.  This option can be used to ping
    a local host through an interface that has no route.

SO_DEBUG

            When enabled, the kernel keeps track of detailed
    information about the packets sent and received by TCP for the socket

但是在traceroute中，如果我在命令行中提供-d选项，则还启用了SO_DONTROUTE选项。另外，当我启用-r选项时，-d也启用。我可以知道为什么吗？

Answer 1

我没有看到两个标志之间有任何明确的关系，因此(可能)这是一些特定于实现的行为，甚至可能是错误。

我已经在安装了默认traceroute的Ubuntu 14.04计算机上运行了traceroute -d 8.8.8.8-Modern traceroute for Linux, version 2.0.20, Aug 19 2014并设法达到8.8.8.8。使用-r标志，由于机器无法找到Network is unreachable，所以traceroute失败，并显示8.8.8.8错误消息。

查看strace和traceroute -r的traceroute -d，我还验证了一个调用仅 setsockopt(3, SOL_SOCKET, SO_DONTROUTE, [1], 4)，而另一个调用仅 setsockopt(3, SOL_SOCKET, SO_DEBUG, [1], 4)。

Van Jacobson的traceroute的official(？)来源应以相同的方式运行。这是(一部分)解析命令行开关的代码:

case 'r':
    options |= SO_DONTROUTE;
    break;

case 'd':
    options |= SO_DEBUG;
    break;

这是套接字选项:

if (options & SO_DEBUG)
    (void)setsockopt(s, SOL_SOCKET, SO_DEBUG, (char *)&on,
        sizeof(on));
if (options & SO_DONTROUTE)
    (void)setsockopt(s, SOL_SOCKET, SO_DONTROUTE, (char *)&on,
        sizeof(on));

但也许来源是不同的版本。