DHCP leases after deleting VM

iandkiandk Hosting ProviderOG

Hi,
I've asked this question a while back, but maybe someone has a better solution for my problem.

I recently configured radvd and DHCP on my Proxmox server to simplify IP management and further automate provisioning.

At first sight this works fine, but I encountered the following problem.

I have several single IPv4's and an IPv6 subnet, which are also allocated to the clients without any problems.

Now the situation is that I often create VMs, run them shortly and then delete them again.
Each time a lease is requested, which is still active afterwards, even if the actual VM was already deleted long ago.

The DHCP server indicates that I have no more IPs until I delete the leases manually.

I could set the lease time to a low value and configure a static IP for the MAC address of important VMs.
But that would require manual setup.

Is there a way to keep the IPs static as long as the MAC of a VM doesn't change? Or some other better way?

Regards
iandk

Comments

  • The solution is to set the lease time to a low value. A VM that is running will renew its lease before it expires.

  • iandkiandk Hosting ProviderOG

    @tetech said:
    The solution is to set the lease time to a low value. A VM that is running will renew its lease before it expires.

    right, but what happens if I shut down one of the VMs and spin up a new VM in the meantime?
    The IP of the first server would change, right?

  • InceptionHostingInceptionHosting Hosting ProviderOG

    yes, its called a DHCP reservation, the reservations are MAC bound, you just need to setup the dhcp reservations once, I am about 90% sure that you can do this through the proxmox web ui.

    https://inceptionhosting.com
    Please do not use the PM system here for Inception Hosting support issues.

  • iandkiandk Hosting ProviderOG

    @AnthonySmith said:
    yes, its called a DHCP reservation, the reservations are MAC bound, you just need to setup the dhcp reservations once, I am about 90% sure that you can do this through the proxmox web ui.

    Unfortunately I don't think so, as far as I know, there is no integration of DHCP for Proxmox

  • @iandk said:

    @AnthonySmith said:
    yes, its called a DHCP reservation, the reservations are MAC bound, you just need to setup the dhcp reservations once, I am about 90% sure that you can do this through the proxmox web ui.

    Unfortunately I don't think so, as far as I know, there is no integration of DHCP for Proxmox

    Have you tried something like this? https://www.danpros.com/2017/09/assign-static-ips-to-kvm-guests-using-dhcp-in-proxmox

  • iandkiandk Hosting ProviderOG

    Yes that's how I currently do it, but my goal would be, that each VM gets an IP assigned via DHCP which it keeps until I delete it or the MAC changes, without setting the static entries manually.

  • InceptionHostingInceptionHosting Hosting ProviderOG

    ok well its only a config file, if your really not comfortable about that then disable DHCP on proxmox setup a tiny VPS running dhcpd + webmin and manage the leases via that.

    https://inceptionhosting.com
    Please do not use the PM system here for Inception Hosting support issues.

  • iandkiandk Hosting ProviderOG

    Thank you for your input, looks like the best option would be to set the lease time to a low value und configure static leases for my important VMs.

  • @iandk said:
    Yes that's how I currently do it, but my goal would be, that each VM gets an IP assigned via DHCP which it keeps until I delete it or the MAC changes, without setting the static entries manually.

    From the DHCP server's perspective there's either a reservation or there isn't. If there's no reservation and a lease expires then you have no guarantee. So you need to either (a) set a short lease and not switch off the VM, (b) set a long lease and have a script that releases the lease when the VM is destroyed, (c) have a script that creates a reservation when the new MAC is assigned.

    That said, some DHCP servers have sticky allocations, which means that the DHCP server gives out the oldest out-of-lease IP rather than the lowest available IP. This means that when a computer requests a lease it will get the old IP back unless the pool was exhausted. At least pfSense works in this way.

  • Well, You can configure DHCP server to only allocate specific IP addresses to VM's with specific MAC addresses.
    Which removes this problem and you are set.

    I do it mostly by API, a external software knows the IP pool and does it this way.

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