IP change on statically configured Windows VM on KVM on CentOS physical server

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cpiro
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IP change on statically configured Windows VM on KVM on CentOS physical server

Post by cpiro » 2021/11/04 07:51:10

Hey, new here, new to CentOS overall as well, trying to find my way through, i am guessing this forum might help in that :)

So, i have an issue id like to describe and a couple questions that i would eventually want to lead me to understanding what exactly happened.

My setup involves physical servers running CentOS 7 with KVM and a couple Windows Server VMs. My gateway is a Debian server doing routing, firewall, DNS, OSPF etc..
These servers and I think the VMs too where Kickstarted with Ansible back in the day (not by me) so I still have a lot to find out regarding the setup.

I have a VLAN with a dozen servers (Windows server VMs on the CentOS physical servers i mentioned above) which are statically configured with IP addresses from the /24 I have for that vlan (lets say 172.25.0.0/24).

Now, i was introducing a new server to the VLAN (lets say our VLAN is 111).

This was a Windows 2016 baremetal server with a nic teaming.

So in our setup we have, 3 servers in VLAN 111 as follows:

Server1 - Windows server VM on KVM on CentOS 7(172.25.0.15)
Server2 - New baremetal Windows server (172.25.0.16)
Server3 - Windows server VM on KVM on CentOS 7(172.25.0.17)

There is no DHCP enabled for the servers in Windows, they are, as i mentioned earlier, statically configured (again, i think. I mean ipv4 settings on the nic in windows are statically configured) with the IPs mentioned above and their gateway which is my Debian Wheezy backports server.

The series of events that took place and that i have to describe before asking my questions is as follows:

Server2, the new server, was configured with a primary IP (172.25.0.16) correctly but also wrongly/mistakenly configured with a secondary IP in the nic teaming on windows which is already configured on Server1, 172.25.0.15.

This rendered Server1 unusable and when checking ARP on the debian gateway I could see the 172.25.0.15 arp entry as incomplete.

Now one of the weird things that I'm wondering about takes place, I VNC to the Server1 VM through KVM to check IP config and I see 172.25.0.17 configured!? At this point, Server3 is still working as it should for some reason, even if Server1 got its IP (172.25.0.17), but how? Since DHCP is disabled on Windows, how would it get another IP (another question if this was gratuitous arp and also why it got an IP that was already assigned?!)

So moving on, I corrected the IP config on Server1 to 172.25.0.15 and voila Server1 is back up but, Server3 lost connectivity automatically after the change! Checking ARP entries on the gateway I can see 172.25.0.17 as incomplete. I tried to delete the arp entry with sudo arp -d 172.25.0.17 but nothing happened.

Lastly I VNC'd to Server3 and "surprisingly", the IP config was still at 172.25.0.17, but no connectivity (well, no ARP in the ARP table on the gateway :)) so I disable and re-enable the nic and all is back in order...

Im trying to understand everything that happened but im getting lost on the way. My main questions are, firstly why would Server1 get an already allocated IP (172.25.0.17) and how, and secondly, why would Server3 stop working only after removing the same IP from Server1?

I have to mention that there is IFUP running on the server and there's a dozen scripts in /etc/sysconfig/network-scripts which i do not know fully well what they do yet. Is there something that would be able to change the server's nic IP address, be that a virtual nic, on a windows server VM on KVM while DHCP is off? Could you pinpoint where or what I should be looking for?

I hope all this makes sense. If not please do let me know ill try to explain as much as i can.

Thanks.

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TrevorH
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Re: IP change on statically configured Windows VM on KVM on CentOS physical server

Post by TrevorH » 2021/11/04 17:33:32

If these are all Windows servers and all of them are set up with static ip addresses then I think you are asking in the wrong forum.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

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jlehtone
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Re: IP change on statically configured Windows VM on KVM on CentOS physical server

Post by jlehtone » 2021/11/04 18:26:35

Like Trevor said, we do not guess what wild beasts do. However, care and feeding of CentOS is something we know about.

If the CentOS is managed with Ansible, then you should find out what the plays do. If it isn't then getting the plays back in action would be worth the effort.

Meanwhile, you can query what configuration does the host have:
* systemctl status NetworkManager is likely saying "not active", if the system has been configured with network.service
* ip ro shows routes
* ip li shows "links", interfaces
* brctl show lists bridges. KVM does use bridges.

cpiro
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Re: IP change on statically configured Windows VM on KVM on CentOS physical server

Post by cpiro » 2021/11/04 20:16:39

TrevorH wrote:
2021/11/04 17:33:32
If these are all Windows servers and all of them are set up with static ip addresses then I think you are asking in the wrong forum.
Youuu…Do have a point :D

But, what i want to get out of the way ultimately is if anything would be able to change that static nic ipv4 config from the CentOS physical.

Hence why i posted here :)

Edit: Plus, i do want, wholeheartedly, to start learning a lot more about CentOS, even with the abndonement now, and linux in general.

cpiro
Posts: 3
Joined: 2021/11/04 07:43:46

Re: IP change on statically configured Windows VM on KVM on CentOS physical server

Post by cpiro » 2021/11/04 20:53:09

jlehtone wrote:
2021/11/04 18:26:35
Like Trevor said, we do not guess what wild beasts do. However, care and feeding of CentOS is something we know about.

If the CentOS is managed with Ansible, then you should find out what the plays do. If it isn't then getting the plays back in action would be worth the effort.

Meanwhile, you can query what configuration does the host have:
* systemctl status NetworkManager is likely saying "not active", if the system has been configured with network.service
* ip ro shows routes
* ip li shows "links", interfaces
* brctl show lists bridges. KVM does use bridges.
Im on to that. I think they were just “kickstarted” which means the physicals where just spawn and configured with a playbook. I do have access to the ansible server so ill start from there.

As for the networking configuration, ill post something here that might be helpful soon.

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TrevorH
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Re: IP change on statically configured Windows VM on KVM on CentOS physical server

Post by TrevorH » 2021/11/04 22:59:33

But, what i want to get out of the way ultimately is if anything would be able to change that static nic ipv4 config from the CentOS physical.
No.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

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