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  • Router Alert options on IGMPv2 packets

    - by Scakko
    I'm trying to forge an IGMPv2 Membership Request packet and send it on a RAW socket. The RFC 3376 states: IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol number of 2. Every IGMP message described in this document is sent with an IP Time-to-Live of 1, IP Precedence of Internetwork Control (e.g., Type of Service 0xc0), and carries an IP Router Alert option [RFC-2113] in its IP header So the IP_ROUTER_ALERT flag must be set. I'm trying to forge the strict necessary of the packet (e.g. only the IGMP header & payload), so i'm using the setsockopt to edit the IP options. some useful variables: #define C_IP_MULTICAST_TTL 1 #define C_IP_ROUTER_ALERT 1 int sockfd = 0; int ecsockopt = 0; int bytes_num = 0; int ip_multicast_ttl = C_IP_MULTICAST_TTL; int ip_router_alert = C_IP_ROUTER_ALERT; Here's how I open the RAW socket: sock_domain = AF_INET; sock_type = SOCK_RAW; sock_proto = IPPROTO_IGMP; if ((ecsockopt = socket(sock_domain,sock_type,sock_proto)) < 0) { printf("Error %d: Can't open socket.\n", errno); return 1; } else { printf("** Socket opened.\n"); } sockfd = ecsockopt; Then I set the TTL and Router Alert option: // Set the sent packets TTL if((ecsockopt = setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_TTL, &ip_multicast_ttl, sizeof(ip_multicast_ttl))) < 0) { printf("Error %d: Can't set TTL.\n", ecsockopt); return 1; } else { printf("** TTL set.\n"); } // Set the Router Alert if((ecsockopt = setsockopt(sockfd, IPPROTO_IP, IP_ROUTER_ALERT, &ip_router_alert, sizeof(ip_router_alert))) < 0) { printf("Error %d: Can't set Router Alert.\n", ecsockopt); return 1; } else { printf("** Router Alert set.\n"); } The setsockopt of IP_ROUTER_ALERT returns 0. After forging the packet, i send it with sendto in this way: // Send the packet if((bytes_num = sendto(sockfd, packet, packet_size, 0, (struct sockaddr*) &mgroup1_addr, sizeof(mgroup1_addr))) < 0) { printf("Error %d: Can't send Membership report message.\n", bytes_num); return 1; } else { printf("** Membership report message sent. (bytes=%d)\n",bytes_num); } The packet is sent, but the IP_ROUTER_ALERT option (checked with wireshark) is missing. Am i doing something wrong? is there some other methods to set the IP_ROUTER_ALERT option? Thanks in advance.

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