讨论，关于怎么理解计算 Internet Checksum

[gloomyfish]

相关rfc文档：refer to RFC1071
In outline, the Internet checksum algorithm is very simple:

(1) Adjacent octets to be checksummed are paired to form 16-bit
integers, and the 1's complement sum of these 16-bit integers is
formed.

(2) To generate a checksum, the checksum field itself is cleared,
the 16-bit 1's complement sum is computed over the octets
concerned, and the 1's complement of this sum is placed in the
checksum field.

(3) To check a checksum, the 1's complement sum is computed over the
same set of octets, including the checksum field. If the result
is all 1 bits (-0 in 1's complement arithmetic), the check
succeeds.
16的校验和开发当初是为用在PDP-11 16位的机器上，你怎么理解RFC文档中上面的第三点
不要给我贴一堆代码，我也会那样！写出你自己的理解~~~
大家乱谈~~~

[nuaawenlin]

checksum = 1+2+3=6=0000 0000 0000 0110
checksum = ~checksum = 1111 1111 1111 1001.


接收后校验

checksum = 1111 1111 1111 1001 + 0000 0000 0000 0110 = 1111 1111 1111 1111 = 0

[gloomyfish]

其他还有人说话吗，楼上的例子好经典~~~

[gloomyfish]

怎么没人回帖，谈谈TCP,IP的checksum目前做法的利弊，怎么在gateway中增量计算
像TTL一样的修改，字节交换的算法，怎么提高改进~~