this issue was raised before in bug 1633562, and closed as invalid because a side effect of isc-dhcp doing 'preinit6' is clearing any existing global ipv6 addresses from the interface, which definitely is not desirable when using RA to get the address.
-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to isc-dhcp in Ubuntu. https://bugs.launchpad.net/bugs/1764478 Title: dhclient in 'stateless' mode does not wait for ipv6 dad Status in isc-dhcp package in Ubuntu: New Status in isc-dhcp source package in Trusty: New Status in isc-dhcp source package in Xenial: New Status in isc-dhcp source package in Artful: New Status in isc-dhcp source package in Bionic: New Bug description: [impact] when configuring an interface in ifupdown to use 'inet6 auto' (SLAAC), the option 'dhcp 1' can also be used, which will use isc-dhcp-client to perform 'stateless' dhcpv6, which does not get a dhcpv6 address, only config info, like DNS domain and server, etc. bug 1633479 fixed isc-dhcp-client to properly bring up and wait for the interface's ipv6 Duplicate Address Detection (DAD) to complete, which is required for isc-dhcp-client to be able to open a socket and begin broadcasting DHCPv6 requests. However, that fix is skipped when isc-dhcp-client is used in 'stateless' mode, so it fails in exactly the same way, for the same reason; isc-dhcp-client needs to be updated to perform the 'PREINIT6' call to the dhclient script, which properly sets up the interface for dhclient to use. Without that setup, isc-dhcp-client in DHCPv6 'stateless' mode will always fail immediately when the interface it's using is down. If the interface is up, it will already have completed DAD and dhclient will work. [test case] configure ifupdown with: auto eth0 iface eth0 inet6 auto dhcp 1 replacing eth0 with the interface to test. Make sure the interface is down, then ifup the interface. isc-dhcp-client will fail claiming that: no link-local IPv6 address for eth0 Alternately, ifupdown can be bypassed; for an interface that is currently down, do: $ sudo dhclient -6 -S eth0 which will fail immediately (the -S param uses 'stateless' mode). [regression potential] changing isc-dhcp-client to perform PREINIT6 adds a new point of failure for doing DHCPv6, so there is the potential to break existing DHCPv6 clients if the preinit fails. However, 'normal' DHCPv6 already does preinit6 - this only adds it to 'stateless' DHCPv6, so the failure potential should be limited to only users of 'stateless' DHCPv6, and those users are likely already seeing failures as described in this bug. [other info] This is related to bug 1633479 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1764478/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
