[SOLVED] New Vm gets wrong IP address using DHCP

[tvlot]

Been playing with proxmox for a bit now and my initial VMs were problem free fun. Today I added a new VM and when it booted, using DHCP like the others, it comes up with a 192.168.8 IP, where I am using a 192.168.1 network. As I'm new to Proxmox I have no clue (but the very obvious "Did I use the right vmbr?" (I did)), where to start digging,

Any suggestions ?

 

[Spoonman2002]

- what ip address is given to an existing/old vm when you release/renew it's ip ?
- are you using powerline adapters by any chance (create a network via the wall outlets) ?

 

[tvlot]

When I release/renew I keep getting the 192.168.8 range of addresses. Infrastructure wise I have one physical NIC in my proxmox server configured (which works as expected for the other VMs build earlier on the 192.168.1 network. The NIC is cabled into a BT Wifi extender things which has a single ethernet port that I'm using.

 

[Spoonman2002]

What is your "main" network subnet? You mentioned 192.168.1.0/24
Make sure that Wifi extender device is also in the 192.168.1.0/24 subnet.
Maybe it acts as a DHCP server with 192.168.8.0/24 subnet (or a device behind that extender)?
You better check that all your network devices are on the same subnet, not mixed.

 

[tvlot]

What is your "main" network subnet? You mentioned 192.168.1.0/24
Make sure that Wifi extender device is also in the 192.168.1.0/24 subnet.
Maybe it acts as a DHCP server with 192.168.8.0/24 subnet (or a device behind that extender)?
You better check that all your network devices are on the same subnet, not mixed.

All my devices, including the extender and anything attached to it are on 192.168.1.0/24. The only thing that gets the 192.168.8.0/24 address is this new VM :-(

 

[Axl_fzetafs]

What's the VM's OS? You may get the IP address of the DHCP server and know the OUI, from there you may guess what's the vendor's machine of the DHCP server. In Windows it's easy (ipconfig /all), in Linux should be easy as well.

https://www.cyberciti.biz/faq/linux-find-out-dhcp-server-ip-address/

Once you know the IP address of the server, then ping it and check the arp table.

 

[tvlot]

The VM is running a Linux OS. I set the IP to a manual one in the right subnet, but it isn't reachable. Clearly something is wrong with my Proxmox config for this VM that, despite using the same vmbr0 as all the others, which is the same NIC the Proxmox server uses to reach this subnet, it created a VM that cannot reach the subnet all it's friends are on. There is no DHCP server in 192.168.8.x as I don't have that subnet anywhere in my setup :-(

 

[tvlot]

Just creating a new VM to test more, and noticed the only (obvious) difference the "broken" VM has compared to the working ones, is that is uses EFI instead of the default SeaBIOS. Could this lead to weird network behaviour?

 

[Spoonman2002]

Just creating a new VM to test more, and noticed the only (obvious) difference the "broken" VM has compared to the working ones, is that is uses EFI instead of the default SeaBIOS. Could this lead to weird network behaviour?

OVMF/UEFI is the vm bootloader, I don't think this is the problem.
What ip address did the newly created vm get (no ip I guess)?

- have you checked your network infrastructure (routers, extenders, IoT stuff, containers, Docker) if there is an active second DHCP server somewhere? If so, disable it.
- make sure you are not connected to your neighbours network in any way.

 

[tvlot]

Just build 2 identical quick test VMs using Ubuntu 22.10. One on EFI and one using BIOS. They both end up grabbing a 192.168.8.0 IP :-(

A previous test Proxmox install I had had a similar issue, but it manifested after I tested a firewall VM (forget which) on it. At the time i had a ton of unexpected interfaces suddenly on the Proxmox system, I have some now (all fwbr named) no clue where they came from or if they are expected. I also notice a "tap" interface I didn't have before.

 

[tvlot]

It took some digging around but in the end I found that a travel router I have enabled to make a Ring doorbell work, had gone mental and decided it needed to do DHCP bits no one wanted. Rebooting it into sanity fixed this issue as well.

Sorry for bugging you all with my network mess

 

[Axl_fzetafs]

It took some digging around but in the end I found that a travel router I have enabled to make a Ring doorbell work, had gone mental and decided it needed to do DHCP bits no one wanted. Rebooting it into sanity fixed this issue as well.

Sorry for bugging you all with my network mess

That's why knowing the IP address and the MAC address of the DHCP server could have pointed you out who the hell was that ghost...