When I try to use nmap:
# nmap -sP -6 FE80::1-234
[...] Failed to resolve given IPv6 hostname/IP: FE80::1-234. Note that you can't use '/mask' or '[1-4,7,100-]' style ranges for IPv6.[...]
What other tool can I use?
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There was an interesting presentation from Metasploit on this recently (blog post is here)
From that there are a number of techniques that nmap can use to identify IPv6 hosts on the local network which could be of use to you
Scanning your local subnet for all IPv6-enabled systems in one shot:
Port scanning the top 10000 ports on these assets:
Write a short script to generate the IPv6 range you want to scan, then pass that to nmap using
IPv6 Target File
For the script (if you need help with this part) do a for loop:
The only limit I see with this setup, is that you will have to calculate the appropriate ip range, which might not be simple, depending on the network design.