From: thedeerhunter1978@movie.uni   
      
   This question is in regards to the iphdr struct that can be found in   
   /usr/include/linux/ip.h and /usr/include/netinet/ip.h.  In some   
   open-source projects, I have seen this header mapped onto packet data,   
   to extract individual IPv4 header fields, like so:   
      
      
       struct iphdr   
       {   
           unsigned int ihl:4;   
           unsigned int version:4;   
           uint8_t tos;   
           uint16_t tot_len;   
           uint16_t id;   
           uint16_t frag_off;   
           uint8_t ttl;   
           uint8_t protocol;   
           uint16_t check;   
           uint32_t saddr;   
           uint32_t daddr;   
       };   
      
      
       struct iphdr* hdr = (struct iphdr*) packet_data;   
        
       uint32_t ipv4_src_addr = hdr->saddr;   
       uint32_t ipv4_dst_addr = hdr->daddr;   
         
         
   Is this safe?  Given that the packet data could start at any memory   
   location, what guarantee is there that the 32-bit 'saddr' and 'daddr'   
   fields are properly aligned in memory at 32-bit boundaries?   
      
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