ip netns add nsx
ip li add vethx type veth peer name peerx netns nsx
ip li set vethx up
ip -6 addr add fd00::1/64 dev vethx
ip netns exec nsx ip li set lo up
ip netns exec nsx ip li set peerx up
ip -6 netns exec nsx ip addr add fd00::2/64 dev peerx
ip netns exec nsx ip -6 route add default via fd00::1 dev peerx

ip -6 rule add fwmark 1088 table 100
ip -6 route add local default dev vethx table 100

ip6tables -t mangle -A PREROUTING -i vethx -p udp -j TPROXY -s fd00::2 --on-ip fd00::1 --on-port 10000 --tproxy-mark 1088

root@localhost:/home/user# glider -verbose -listen tproxy://[fd00::1]:10000 -forward socks5://127.0.0.1:9000
2021/10/11 21:38:25 group.go:186: [group] only 1 forwarder found, disable health checking
2021/10/11 21:38:25 server.go:78: [tproxyu] listening UDP on [fd00::1]:10000
2021/10/11 21:38:25 server.go:78: [tproxyu] listening UDP on 10.0.0.1:10000
2021/10/11 21:39:00 server.go:84: [tproxyu] read error: unable to obtain original destination: %!s(<nil>)
2021/10/11 21:39:05 server.go:84: [tproxyu] read error: unable to obtain original destination: %!s(<nil>)
2021/10/11 21:39:10 server.go:84: [tproxyu] read error: unable to obtain original destination: %!s(<nil>)

root@localhost:/home/user# ip netns exec nsx dig @2606:4700:4700::1111 g.co
; <<>> DiG 9.16.15-Debian <<>> @2606:4700:4700::1111 g.co
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached