curtin 0.1.0~bzr425-0ubuntu was installed out of xenial-updates and the non-default MTU does indeed get into /e/n/i.
>From a deployed node's /e/n/i: auto ens7f0 iface ens7f0 inet manual bond-xmit_hash_policy encap3+4 bond-mode 802.3ad bond-master bond2 mtu 9202 bond-lacp_rate fast bond-miimon 100 auto ens7f1 iface ens7f1 inet manual bond-xmit_hash_policy encap3+4 bond-mode 802.3ad bond-master bond2 mtu 9202 bond-lacp_rate fast bond-miimon 100 auto bond2 iface bond2 inet6 manual address fd06:ffe0:6779::2:0:9/64 bond-xmit_hash_policy encap3+4 bond-mode 802.3ad bond-slaves none mtu 9202 bond-lacp_rate fast hwaddress ether 0c:c4:7a:b7:24:34 bond-miimon 100 auto br-bond2 iface br-bond2 inet6 static address fd06:ffe0:6779::2:0:9/64 mtu 9202 hwaddress ether 0c:c4:7a:b7:24:34 bridge_ports bond2 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1609861 Title: IPv6 MTU not applied correctly for pure IPv6 interfaces To manage notifications about this bug go to: https://bugs.launchpad.net/curtin/+bug/1609861/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs