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copied!<p>When <code>accept()</code> returns <code>-1</code>, <code>errno</code> will be set to indicate what specific error occurred. Please call <code>perror("accept")</code> for an easy way to see what the error was, and update your question with the results.</p> <p>Also, please note that <code>accept()</code> must be called on a socket that has been:</p> <ul> <li>Created using the <code>socket()</code> call. (you should pass <code>PF_INET6</code> for the first argument of your socket to create an IPv6 protocol family socket)</li> <li>Bound, using <code>bind()</code> using a <code>struct sockaddr_in6</code> parameter as the 2nd parameter (with its <code>sin6_family</code> set to <code>AF_INET6</code> for IPv6 to indicate you will be binding to an IPv6 address). Remember to zero out the <code>sin6_zero</code> field first. One strategy would be to zero the entire sockaddr structure, which would set the IPv6 address to IN6ADDR_ANY, which means you would just have to set the port and the address family.</li> <li>Listening, by means of calling <code>listen()</code></li> </ul> <p>If you are still having trouble, post the code you have so far.</p> <p>If I had to guess (since you haven't posted any code), I think if it works with IPv4 and gets to the point where it can <code>accept()</code> a connection, but IPv6 connection <code>accept()</code> calls return <code>-1</code>, I think it's likely that you aren't passing <code>accept()</code> a large enough <code>struct sockaddr</code> for it to work.</p> <p>For example, the following code:</p> <pre><code>printf("sizeof(struct sockaddr_in) = %ld\n", sizeof(struct sockaddr_in)); printf("sizeof(struct sockaddr_in6) = %ld\n", sizeof(struct sockaddr_in6)); </code></pre> <p>Prints (on my system):</p> <pre><code>sizeof(struct sockaddr_in) = 16 sizeof(struct sockaddr_in6) = 28 </code></pre> <p>If you are only giving <code>accept()</code> enough room to write out an IPv4 address, it will fail when it accepts an IPv6 connection. Make sure you allocate either a <code>struct sockaddr_in6</code> or a <code>struct sockaddr storage</code>, and ensure the size argument is correct.</p>

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