confusion about RELAY EXTEND cell payloads & other little Tor questions

[Christian Seberino]

Tor spec says Relay cell payloads consist of:

relay command
streamID
digest
length
data

Yet in another place it says Relay *EXTEND* cell payloads consist of:

address
port
onion skin
indentify fingerprint

Are EXTENDs somehow special & have different payloads than other Relay cells?

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Also, why is address field of EXTEND hard wired to IPv4 only? What about
IPv6?

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Some places talk about seeding a hash.  I assume this means adding unique
stuff to a SHA1 hash?? Where are the details of 'seeding hashes' found?



THANKS!

Chris