Question

I have written a traceroute program written on OS X.
I am trying to port it to GNU/Linux.

[@osx]
>> sudo bin/traceroute www.google.com

Warning: www.google.com has multiple addresses; using 173.194.69.99
...

To make it compile on GNU/Linux, I added _GNU_SOURCE feature test macro.

[@ubuntu]
>> sudo bin/traceroute www.google.com

error setting socket options: Invalid argument

The issue is at:

 85     send_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
 86     if(send_socket == -1){
 87        fprintf(stderr, "\ncannot create send socket");
 88        freeaddrinfo(dest_addrinfo_collection);
 89        return EXIT_FAILURE;
 90      }
 91     error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(int));
 92     if(error != 0){
 93        perror("\nerror setting socket options");
 94        freeaddrinfo(dest_addrinfo_collection);
 95        return EXIT_FAILURE;
 96      }

Looks like setsockopt(...) cannot recognize IP_TTL as socket option.
However I see IP_TTL as a socket option for IPPROTO_IP level.

I am using SOCK_DGRAM as my sending socket to avoid preparing my own ICMP packet.

Answer 1

My mistake, my ttlvariable was an unsigned short.

-    error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(int));
+    error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(unsigned short));

---

UPDATE

In addition I had to option_len was different for different platforms.

-    error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(unsigned short));
+#if defined(__APPLE__)
+    error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(&ttl));
+#elif defined(__linux)
+    error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
+#endif

---

UPDATE

-  unsigned short          ttl = 1;
+  socklen_t               ttl = 1;

-#if defined(__APPLE__)
-    error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(&ttl));
-#elif defined(__linux)
     error = setsockopt(send_socket, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
-#endif