After I have deployed the vMX on a CentOS 7.4 host that has an IPv6 address for management, I noticed that IPv6 stopped working when the vMX was started. In my case, the IPv6 address was originally on the interface bond0. When the vMX starts a bridge interface is created which by default is named br-ext. The host management IP will be moved to the new bridge interface. When checking, the IPv6 address on bond0 remained and the br-ext interface did not have the IPv6 address.
First, I deleted the IPv6 address from bond0:
ip -6 addr del ffff::ffff/64 dev bond0
I then tried to add the IPv6 address to br-ext:
ip -6 addr add ffff::ffff/64 dev br-ext
When I tried to add it I got this error:
RTNETLINK answers: Permission denied
After checking, the interface has IPv6 disabled. I then enabled IPv6 for the interface:
echo 0 > /proc/sys/net/ipv6/conf/br-ext/disable_ipv6
I could then add the IP address to the interface again.