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Packet & bit fields templates

Packet — IPv6 Fixed Header, Forty Bytes

Ten words with two 128-bit addresses, which is the case that makes the wrapping question unavoidable: each address is four whole words and is drawn as such. Useful as a starting point for extension-header diagrams, where the fixed part above stays and the rest changes.

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IPv6 fixed header (RFC 8200)32-bit words · 10 words · 320 bits laid out · 8 fields · ruler shows ABSOLUTE bit indicesMSB-first: bit 0 is the most significant bit of each 32-bit word, drawn leftmost; indices increase to the right.In both orders the most significant bit of a word is the leftmost column — only the numbering flips.Layout checks passed — 8 fields, 10 words, 320 bits: no gaps, no overlaps, nothing past the last word.MSBLSBword 0bits 0–31+0B012345678910111213141516171819202122232425262728293031word 1bits 32–63+4B3233343536373839404142434445464748495051525354555657585960616263word 2bits 64–95+8B6465666768697071727374757677787980818283848586878889909192939495word 3bits 96–127+12B96979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127word 4bits 128–159+16B128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159word 5bits 160–191+20B160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191word 6bits 192–223+24B192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223word 7bits 224–255+28B224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255word 8bits 256–287+32B256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287word 9bits 288–319+36B288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319Versionbits 0–3 = 6Traffic classbits 4–11 · 8bFlow labelbits 12–31 · 20bPayload lengthbits 32–47 · 16bNext headerbits 48–55 · 8bHop limitbits 56–63 · 8bSource address…bits 64–191 · 128b…Source address…bits 64–191 · 128b…Source address…bits 64–191 · 128b…Source addressbits 64–191 · 128bDestination address…bits 192–319 · 128b…Destination address…bits 192–319 · 128b…Destination address…bits 192–319 · 128b…Destination addressbits 192–319 · 128bNo overlaps: each of the 320 checked bits belongs to at most one field.No gaps: bits 0–319 fully covered by 8 fields.Every field ends inside the 10-word layout.

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title "IPv6 fixed header (RFC 8200)"
width 32
bitorder msb
words 10

0-3:   Version = 6
4-11:  Traffic class
12-31: Flow label

32-47: Payload length
48-55: Next header
56-63: Hop limit

64-191:  Source address
192-319: Destination address