Reading ICMP reply with select in Linux using C++

Question

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.

https://i.stack.imgur.com/exdAI.png wireshark screenshot

For testing my program I am using Ubuntu 12.10 running on VirtualBox 4.2.6 and GN3 for a virtual network.

My source 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(&mySet);
        FD_SET(mysocket, &mySet);

        retval = select(mysocket+1, &mySet, NULL, NULL, &tv);

        cout << "Errno after select:" << strerror(errno) << endl;

        if(retval == -1) {
            cerr << "select error" << endl;
            break;
        }
        else if (retval) {
            if((length = recvfrom(mysocket, buffer, MAX, 0, result->ai_addr, &(result->ai_addrlen))) == -1) {
                cerr << "Error: while receiving data." << endl;
            }
            else {
                cout << "good" << endl;

                ipRec = (struct iphdr*) buffer;
                icmpRec = (struct icmphdr*) (buffer + ipRec->ihl * 4);

                cout << "the packet." << " PID: " << ntohs(icmpRec->un.echo.id) << " Seq: " << ntohs(icmpRec->un.echo.sequence) << endl;

                if ((icmpRec->type == ICMP_ECHOREPLY) && (ntohs(icmpRec->un.echo.id) == pid) && (ntohs(icmpRec->un.echo.sequence) == (seq - 1))) {
                    minBuff = lengthBuff;
                }
            }
        } else {
            // getting here all the time = select times-out and reads no data

            cout << "mysocket:" << mysocket << endl;
            cout << "retval:" << retval << endl;
            maxBuff = lengthBuff;
            break;
        }
    } while (!((icmpRec->type == ICMP_ECHOREPLY) && (ntohs(icmpRec->un.echo.id) == pid) && (ntohs(icmpRec->un.echo.sequence) == (seq - 1))));

    if (packet)
        delete(packet);
    ...

Thank you for any help.

Note the << operator does not allow a string as its operand. Maybe you are using C++ ? — wildplasser, Dec 29 '12 at 18:02
Fixed the problem. Found the solution in a different thread: http://stackoverflow.com/questions/9688899/icmp-packets-are-not-being-sent-c?rq=1. Changing IPPROTO_RAW to IPPROTO_ICMP fixed it. Now is select reading the ICMP reply packet. — Matej Koleják, Dec 29 '12 at 18:28

score 1 · Accepted Answer · edited May 23 '17 at 11:43

1

Fixed the problem. Found the solution in a different thread: ICMP packets are not being sent C. Changing IPPROTO_RAW to IPPROTO_ICMP fixed it. Now is select reading the ICMP reply packet.

edited May 23 '17 at 11:43

Community

1
1

answered Dec 29 '12 at 18:40

Matej Koleják

123
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Reading ICMP reply with select in Linux using C++

1 Answers1