On my VPSes, the TAP network interface created by OpenVPN has a
randomly-generated IPv6 address with scope stable-privacy.
This address itself is created randomly to prevent tracking users by their IPv6 addresses. But when building a network in DN42, BGP handshakes may originate from this address (rather than your manually assigned link-local address) and fail for mismatching origin/IP.
The solution is to configure the TAP interfaces with sysctl, and disable the
automatic address generation options. OpenVPN can be configured to run sysctl
automatically when creating the interface:
# Add to OpenVPN's config file
script-security 2
up "/bin/sh -c '/sbin/sysctl -w net.ipv6.conf.$dev.autoconf=0 && /sbin/sysctl -w net.ipv6.conf.$dev.accept_ra=0 && /sbin/sysctl -w net.ipv6.conf.$dev.addr_gen_mode=1'"Depending on your Linux distribution, you may need to adjust the path of
/bin/sh and /sbin/sysctl.