MTU in IPv6 is advertised via router advertisements (RA). However, any try to advertise correct MTU to instances in OSP 7 / kilo, in
IPv6 only (not dual stack) does not seem to work.
None of the below steps (see "Diagnostic Steps") seems to advertise the correct MTU - neither on new networks, nor on networks which were created before the below changes. In fact, tcpdump shows that neutron routers don't advertise MTU at all.
MTU is advertised via IPv6 RA, and not via DHCPv6
This is the documentation for MTU settings in the overcloud: https://access.redhat.com/documentation/en/red-hat-enterprise-linux-openstack-platform/7/networking-guide/chapter-17-configure-mtu-settings
Red Hat Enterprise Linux OpenStack Platform 7.0
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