Some upstream IPv6 providers reject NDP replies whose source is a
link-local address (what ndppd and Linux proxy_ndp emit) and require the
advertised global address. Replace the distro ndppd prefix-mode data
plane with an in-tree raw AF_PACKET responder whose NA source is the
target's global address, re-reading a panel-writable rules file while it
runs so vps add/del never restarts it.
- add internal/ndp: minimal NDP responder (NS->NA, DAD handling, correct
ICMPv6 checksum/hop-limit/flags); only answers for target blocks inside
the operator's routed prefix (confines the root responder's trust surface)
- main: ipv6-proxy unit (prefix mode) + ipv6-proxy command + ethernetMAC
pre-check at install so a broken ext_if never hot-loops under Restart=always
- ipv6.go: write ndppd.conf atomically (temp+rename), drop all ndppd daemon
management and its sudoers grants
- mgr/routed_ipv6.go: configure guest v6 before publishing the NDP rule;
pin fe80::1 gateway neighbor, UseGateway=false, local /112 route +
vpsmgr-ipv6.service helper in the guest
- 50-image.sh/80-debian-dev-image.sh: bake UseGateway=false into [IPv6AcceptRA]
bluebluesoda
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