ICMPv6 Checksum calculation

根據IPv6 (RFC 4443 Section2.3) 和 ICMPv6 (RFC2460 Section8.1)

我們需要將上述做相加並取1’s 補數

以下用wireshark packet 來做相加的解說

IPv6 Packet with hex

1. Source Address = ::
2. Destionation = ff02::1
3. Next Header = 58 (ICMPv6)

58 to hex is 0x3a

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ICMPv6 total length is 24

24 to hex is 0x18

1. Upper-Layer Packet Length = 0x18

2. ICMP Data (checksum is 0)

Data = 8200 + 03e8 (7ac1忽略)

接下來就算ICMPv6 checksum

1. Source Address = ::
2. Destionation = ff02::1
3. Next Header = 0x3a
4. Upper-Layer Packet Length = 0x18
5. ICMPv6 Data = 8200 +03e8

sum = ff02 + 0001 + 0x3a + 0x18 +8200 + 03e8

sum = 0x1853D , 1進位補上

sum = 0x853E, 取1's補數

checksum = 0x7ac1 (跟ICMPv6 封包的checksum 一致)

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