[systemd-devel] [PATCH] sd-dhcp: implement IPv4 link-local support

[Tom Gundersen]

On Fri, Feb 28, 2014 at 9:05 AM, Umut Tezduyar Lindskog
<umut.tezduyar at axis.com> wrote:
>> If an IPv4LL address has been acquired, and then a DHCP server becomes
>> available, do we really want to drop the address entirely? At least for
>> IPv6 there's this concept of "deprecated" addresses for this purpose. I am
>> pretty sure that's actually available for IPv4 as well, so maybe we should keep
>> the ipv4ll adderss around and just mark it "deprecated"?
>> This would allow ongoing TCP conenctions to survive, but the kernel wouldn't
>> use the address as source address anymore.
>
> This is a great topic. Patrik has been repeating the importance of it and if we can implement this, it would be a great advantage. As you are saying, we really don't want to drop the LL address immediately in case clients are already connected and using it. We should keep the current connections and never let any more connections on LL. I have played around with routing table and couldn't find a nice solution. It is possible to add route rules for the IP address of current connections but I think that way is way messy. But I will look in to this "deprecated" concept you are referring. Maybe you can give more information.

IPv6 addresses are 'deprecated' by setting prefferred_lft = 0. I
imagine the same should work for IPv4, but I never actually tried.

Cheers,

Tom