On Thu, 05 Oct 2017 00:20:28 +0200 Thomas Haller <[email protected]> wrote:
> On Wed, 2017-10-04 at 11:07 -0700, Stephen Hemminger wrote: > > On Azure (and probably other VM environments), there is a desire to > > cause guest VM to renew DHCP > > lease in response to host infrastructure changes. These include > > things like spinning up > > lots of VM's then suspending them and later unfreezing them as > > needed. The other scenario > > is doing renew following migration. > > > > The current kernel code has a hack to try and simulate link bounce, > > but it doesn't > > work very well and the old ISC DHCP client does nothing. Network > > manager might be > > able to do something better?? > > Hi, > > > link bounce might not work with NetworkManager, in the current form. > > NM has a 5 seconds grace period, during which it ignores carrier going > away. It does so because the link can go down unexpectedly for unknown > reasons. > Actually, after NM changes the MTU, the 5 seconds are extended to 10 > seconds, because [1]. > So, kernel would have to bounce the link for at least 10 seconds. > > Then there is a setting ignore-carrier (`man NetworkManager.conf`). > That causes NM to totally ignore when the link goes down. That setting > is quite common, for example on the package "NetworkManager-config- > server" enables it by default on RHEL. > > Appart from the above obstacles, carrier going away causes the active > connection to disconnect. Later, another (or the same) connection may > autoconnect again. So, that sounds like what you requested, but I don't > think it works well. > > > Thomas > > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1487702 One alternative would be to the hyper-v daemon (doing other services) could invoke a hook or script to request network manager do a renew?
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