[Bug 1013597] Re: No default route for stateful DHCPv6

[Chong Eva]

Apparently, I've done a stupid thing and forgot my Ubuntu Server in AWS
is Server 14. I've upgraded the ubuntu to 16.04 a few months back, but
forgot that it's supposed to be still Ubuntu Server 14.

So I followed the guide https://docs.aws.amazon.com/vpc/latest/userguide
/vpc-migrate-ipv6.html and followed the steps in Ubuntu Server 16. This
got me locked out of my own server, and no matter what I tried
(rebooting, assigned new private IP, tried pinging from other servers in
the same subnet), I still can't get in. SSH ends up in Operation timed
out. I've locked myself out.

I even tried creating an AMI and launch the image into a new instance
but still it won't work, maybe because the network interfaces files are
backed up into the image as well?

What can I do to regain access to my server?

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to ifupdown in Ubuntu.
https://bugs.launchpad.net/bugs/1013597

Title:
  No default route for stateful DHCPv6

Status in ifupdown package in Ubuntu:
  Fix Released
Status in ifupdown source package in Precise:
  Won't Fix

Bug description:
  The default route cannot be provided via DHCPv6, it must be obtained
  from router advertisements. However, when using the dhcp method for
  inet6 in /etc/network/interfaces (e.g. "iface eth0 inet6 dhcp"), ifup
  will set net.ipv6.conf.<IFACE>.accept_ra=0, resulting in no default
  route for IPv6. Instead, it should explicitly set accept_ra=1.

  A workaround is to set it in a post-up script. However, Linux
  apparently only sends router solicitations when the interface is
  brought up, so if unsolicited RA:s are infrequent the host will be
  without a default route until the next RA.

  Another problem is that when bringing the interface down on dual-stack
  hosts, there will be a long timeout. This is because bringing down
  IPv4 also brings the interface link down, and afterwards dhclient
  cannot release the DHCPv6 lease due to the link being down ("RTNETLINK
  answers: Cannot assign requested address"). The workaround is to bring
  the link back up before bringing IPv6 down.

  So the workarounds (which obviously should not be needed) for a dual-
  stack dhcp client look like this:

  iface eth0 inet dhcp
  iface eth0 inet6 dhcp
      up sysctl net.ipv6.conf.$IFACE.accept_ra=1
      pre-down ip link set dev $IFACE up

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1013597/+subscriptions