title: Where is the TTL (Time-To-Live) value defined in the Linux kernel source?
body: <p>I'm having a hard time finding where, in the Linux Kernel source, the TTL is defined. Could someone point out which file that's in?</p>
  
  <p>I'm not sure, but I may have found it at line 820 in <code>net/ipv4/ipconfig.c</code></p>
  
  <pre><code>    /* Construct IP header */
      skb_reset_network_header(skb);
      h = ip_hdr(skb);
      h-&gt;version = 4;
      h-&gt;ihl = 5;
      h-&gt;tot_len = htons(sizeof(struct bootp_pkt));
      h-&gt;frag_off = htons(IP_DF);
      h-&gt;ttl = 64;
  </code></pre>
  
  <p>If I change that and compile the kernel source, would I then be using the new value?</p>
  
  <p>Edit: It may also be defined in <code>include/uapi/linux/ip.h</code> at line 69:</p>
  
  <pre><code>#define IPVERSION   4
  #define MAXTTL      255
  #define IPDEFTTL    64
  </code></pre>