On Wed 10 Jun 2020 at 12:05:57 (-0400), Jim Popovitch wrote:
> Something that has always bugged me (and #debian hasn't yet answered)
>
> What establishes the IPv6 loopback ::1 address, and why is there no need
> for "iface lo inet6 loopback" in /etc/network/interfaces?
AFAICT there's code in linux-source-4.19/net/ipv6/addrconf.c to make
sure that the loopback gets set up early enough. The comments are:
/* The addrconf netdev notifier requires that loopback_dev
* has it's ipv6 private information allocated and setup
* before it can bring up and give link-local addresses
* to other devices which are up.
*
* Unfortunately, loopback_dev is not necessarily the first
* entry in the global dev_base list of net devices. In fact,
* it is likely to be the very last entry on that list.
* So this causes the notifier registry below to try and
* give link-local addresses to all devices besides loopback_dev
* first, then loopback_dev, which cases all the non-loopback_dev
* devices to fail to get a link-local address.
*
* So, as a temporary fix, allocate the ipv6 structure for
* loopback_dev first by hand.
* Longer term, all of the dependencies ipv6 has upon the loopback
* device and it being up should be removed.
Cheers,
David.
