Re: [PATCH 1/2] C/R: Support for IPv6 addresses on network devices

[Dan Smith <danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

BH> Can I ask what the addresses were?

I'm not sure what you mean.  You want to know what the duplicated
address was?  My flawed byteorder adjustment caused me to have two
fe80::X addresses on the restored interface.

I've since added a check to ignore non-global scope addresses, which
works nicely.

BH> Did you move from VM to VM so the underlying NIC MAC address
BH> changed?

No, the MAC doesn't change because I reconstruct the interface on the
other side with the original MAC address.  The netns and netdev code
assume that you're migrating your entire network namespace, which
includes all the devices within.

BH> Again, I don't know your typical user for C/R.  For example, with
BH> IPv4 you save all the addresses, but if one of them was configured
BH> via DHCP, you could have an address conflict when you restore it,
BH> since there's no way to know if it's been handed-out to another
BH> system in the meantime.  Or does a typical C/R user only have
BH> static addresses?

I think that the expectation is that if you're migrating network
connections, you are going to have to be in your own netns and have
your own interface.  If DHCP is in play, then you're going to be
migrating dhclient along with your app anyway.

BH> With IPv6 it gets worse because the link-local will get created
BH> automatically, and if you're in a VM it will probably be somewhat
BH> random.  Then when you move to another VM you'll get another
BH> virtual NIC with a different MAC address.  Since the global
BH> address is going to be based off the same lower 64-bits, you'll
BH> wind-up with a second global in most situations (since you're
BH> restoring the original address).

Well, I'm not sure of your use of "VM" in this case.  I think the
typical usage here will be a container that behaves like a VM.  As I
said above, you'll have your own virtual interface and your MAC
address will go with you.

Right now, I migrate sshd and sendmail around by starting them up in a
container with a veth or macvlan device.  Then, I can move them from
machine to machine while keeping the same interface, MAC and IP
addresses, and without severing connections with the outside world.

-- 
Dan Smith
IBM Linux Technology Center
email: danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org