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POReading ICMP reply with select in Linux using C++
 

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  1. POReading ICMP reply with select in Linux using C++
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    <p>I am sending an ICMP request using C++ and raw sockets to a router and after that I want to read the ICMP reply. My problem is, select() is not receiving the replay and times-out all the time. I am not getting any error (errno is returning success). The router is sending the ICMP reply, because i can see the response using Wireshark. </p> <p><a href="http://i.imgur.com/0Wra1.png" rel="nofollow">http://i.imgur.com/0Wra1.png</a> <em>wireshark screenshot</em></p> <p>For testing my program I am using Ubuntu 12.10 running on VirtualBox 4.2.6 and GN3 for a virtual network.</p> <p>My source code:</p> <pre><code>char buffer[IP_MAXPACKET]; // for the received ICMP reply struct iphdr *ipRec; // ICMP header timeval tv; // timeout fd_set mySet; // descriptor set ... tv.tv_sec = 3; // default time-out 3s tv.tv_usec = 0; int retval; // select ... do { FD_ZERO(&amp;mySet); FD_SET(mysocket, &amp;mySet); retval = select(mysocket+1, &amp;mySet, NULL, NULL, &amp;tv); cout &lt;&lt; "Errno after select:" &lt;&lt; strerror(errno) &lt;&lt; endl; if(retval == -1) { cerr &lt;&lt; "select error" &lt;&lt; endl; break; } else if (retval) { if((length = recvfrom(mysocket, buffer, MAX, 0, result-&gt;ai_addr, &amp;(result-&gt;ai_addrlen))) == -1) { cerr &lt;&lt; "Error: while receiving data." &lt;&lt; endl; } else { cout &lt;&lt; "good" &lt;&lt; endl; ipRec = (struct iphdr*) buffer; icmpRec = (struct icmphdr*) (buffer + ipRec-&gt;ihl * 4); cout &lt;&lt; "the packet." &lt;&lt; " PID: " &lt;&lt; ntohs(icmpRec-&gt;un.echo.id) &lt;&lt; " Seq: " &lt;&lt; ntohs(icmpRec-&gt;un.echo.sequence) &lt;&lt; endl; if ((icmpRec-&gt;type == ICMP_ECHOREPLY) &amp;&amp; (ntohs(icmpRec-&gt;un.echo.id) == pid) &amp;&amp; (ntohs(icmpRec-&gt;un.echo.sequence) == (seq - 1))) { minBuff = lengthBuff; } } } else { // getting here all the time = select times-out and reads no data cout &lt;&lt; "mysocket:" &lt;&lt; mysocket &lt;&lt; endl; cout &lt;&lt; "retval:" &lt;&lt; retval &lt;&lt; endl; maxBuff = lengthBuff; break; } } while (!((icmpRec-&gt;type == ICMP_ECHOREPLY) &amp;&amp; (ntohs(icmpRec-&gt;un.echo.id) == pid) &amp;&amp; (ntohs(icmpRec-&gt;un.echo.sequence) == (seq - 1)))); if (packet) delete(packet); ... </code></pre> <p>Thank you for any help.</p>
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    1. USMatej Koleják
    1. USMatej Koleják
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      1. USJohn M
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    1. CONote the << operator does not allow a string as its operand. Maybe you are using C++ ?
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      1. POReading ICMP reply with select in Linux using C++
      1. USwildplasser
    2. COyes, my fault, its obviously C++ :)
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      1. USMatej Koleják
    3. COwhat is MAX in recvfrom? shouldn't that be IP_MAXPACKET ?
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      1. USIcarus3
 

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