struct ip和struct iphdr之间的区别 [英] Difference between struct ip and struct iphdr

问题描述

我正在尝试了解网络是如何工作的，我正在做一些测试，发送一些软件包......无论如何

I am trying to understand how the network is working, i'm doing some test, sending some package... anyway

我的意思是我可以'找到协议结构和协议标题结构之间的真正区别。

My point is that i can't find the real difference between "protocol" structure and "protocol header" structure.

对于ip结构，它们都大小为20个字节。
但是例如：

For the ip structure, they both sized 20 bytes. but for exemple:

• struct ip 和 struct iphdr size 20 bytes


• struct icmp size 28 bytes


• struct icmphdr size 8 bytes

• struct ip and struct iphdr sized 20 bytes
• struct icmp sized 28 bytes
• struct icmphdr sized 8 bytes

我猜这是 struct icmp 包含 struct ip / iphdr？？

我所看到的每个协议都有相同的结构。
struct udp / struct udphdr ，

And there is the same kind of structure with every protocol i have seen. struct udp / struct udphdr,

是否链接到 IP_HDRINCL 设置为 setsockopt（）？

所以我的问题是它们之间真正的区别是什么？当使用好的时候。

So my question is What is the real difference between them ? And When use the good one.

ip和iphdr struct：

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;
         __u16  tot_len;
         __u16  id;
         __u16  frag_off;
         __u8   ttl;
         __u8   protocol;
         __u16  check;
         __u32  saddr;
         __u32  daddr;
         /*The options start here. */
};

IP HDR

struct ip {
#if BYTE_ORDER == LITTLE_ENDIAN 
    u_char  ip_hl:4,        /* header length */
        ip_v:4;         /* version */
#endif
#if BYTE_ORDER == BIG_ENDIAN 
    u_char  ip_v:4,         /* version */
        ip_hl:4;        /* header length */
#endif
    u_char  ip_tos;         /* type of service */
    short   ip_len;         /* total length */
    u_short ip_id;          /* identification */
    short   ip_off;         /* fragment offset field */
#define IP_DF 0x4000            /* dont fragment flag */
#define IP_MF 0x2000            /* more fragments flag */
    u_char  ip_ttl;         /* time to live */
    u_char  ip_p;           /* protocol */
    u_short ip_sum;         /* checksum */
    struct  in_addr ip_src,ip_dst;  /* source and dest address */
};

此处的ICMP结构代码： https://www.cymru.com/Documents/ip_icmp.h

ICMP structure code here : https://www.cymru.com/Documents/ip_icmp.h

推荐答案

struct ip 和 struct iphdr 是相同底层结构的两个不同定义，来自不同的地方。

struct ip and struct iphdr are two different definitions of the same underlying structure, brought in from different places.

struct ip 在< netinet / ip.h> <中定义/ code>，这是UNIX系统上合理标准的标头。

struct ip is defined in <netinet/ip.h>, which is a reasonably standard header on UNIX systems.

struct iphdr 在< LINUX / ip.h> 。此标头（和结构）是特定于Linux的，并且不会出现在其他操作系统中。

struct iphdr is defined in <linux/ip.h>. This header (and structure) are Linux-specific, and will not be present in other operating systems.

如果您不确定要使用哪个，请使用 struct ip ;使用此结构的代码更有可能移植到非Linux系统。

If you're not sure which one to use, use struct ip; code which uses this structure is more likely to be portable to non-Linux systems.

struct icmp 和 struct icmphdr 是一个更糟糕的情况：

struct icmp and struct icmphdr are a messier situation:

• < netinet / icmp.h> 定义 struct icmp 和 struct icmphdr 。


• < linux / icmp.h> 也定义 struct icmphdr ，具有类似的结构（但通常是不同的字段名称），作为< netinet / icmp.h> 。



• <netinet/icmp.h> defines both struct icmp and struct icmphdr.
• <linux/icmp.h> also defines struct icmphdr, with a similar structure (but, as usual, different field names) as the definition from <netinet/icmp.h>.

首先：不要包含< linux / icmp.h> 除非你有充分的理由。你不能包含两个标题 - 它们会发生冲突 - 大多数软件都会期望netinet定义。

First: Don't include <linux/icmp.h> unless you have a very good reason. You cannot include both headers -- they will conflict -- and most software will expect the netinet definition.

第二： struct icmphdr 顾名思义就是标题。 struct icmp 定义结构化ICMP消息的内容，如目标无法到达的消息。

Second: struct icmphdr is, as the name implies, the header. struct icmp defines the contents of a structured ICMP message, like a destination unreachable message.

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