IP Fragmentation

["A. Ramesh" <aramesh@signafor.com>]

 I am not sure why the kernel allocates 15 more bytes when it creates a fragment packet. The piece of kernel code which does the memory allocated for the new fragment is as follows:

 

 

                 /*
                  *      Allocate buffer.
                  */
 
                 if ((skb2 = alloc_skb(len+hlen+dev->hard_header_len+15,GFP_ATOMIC)) == NULL) {
                         NETDEBUG(printk(KERN_INFO "IP: frag: no memory for new fragment!\n"));
                         err = -ENOMEM;
                         goto fail;
                 }

 

For the first fragment

    len=1480;

    hlen=20 (no IP Options);

    dev->hard_header_len = 14;

 but couldn't figure out the significance of 15 more bytes.

 

-Ramesh