重温网络基础

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/* tcp.h */
struct tcphdr {
    __be16   source;
    __be16   dest;
    __be32   seq;
    __be32   ack_seq;
#if defined(__LITTLE_ENDIAN_BITFIELD)
    __u16    res1:4,
             doff:4,
             fin:1,
             syn:1,
             rst:1,
             psh:1,
             ack:1,
             urg:1,
             ece:1,
             cwr:1;
#elif defined(__BIG_ENDIAN_BITFIELD)
    __u16    doff:4,
             res1:4,
             cwr:1,
             ece:1,
             urg:1,
             ack:1,
             psh:1,
             rst:1,
             syn:1,
             fin:1;
#else
#error    "Adjust your <asm/byteorder.h> defines"
#endif    
    __be16   window;
    __sum16  check;
    __be16   urg_ptr;
};

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/* ip.h */
struct iphdr {
#if defined(__LITTLE_ENDIAN_BITFIELD)
    __u8    ihl:4,
        version:4;
#elif defined (__BIG_ENDIAN_BITFIELD)
    __u8    version:4,
            ihl:4;
#else
#error    "Please fix <asm/byteorder.h>"
#endif
    __u8    tos;
    __be16  tot_len;
    __be16  id;
    __be16  frag_off;
    __u8    ttl;
    __u8    protocol;
    __sum16 check;
    __be32  saddr;
    __be32  daddr;
    /*The options start here. */
};

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/* udp.h */
struct udphdr {
    __be16   source;
    __be16   dest;
    __be16   len;
    __sum16  check;
};