loc_az_hci/docs/network/STATIC_IP_DHCP_COEXISTENCE.md

Static IP vs DHCP Coexistence

Problem

When VMs are configured with static IP addresses (e.g., 192.168.1.188, 192.168.1.60) on a subnet where the router is also running DHCP, there's a risk of IP conflicts:

• Router's DHCP server may assign the same IPs to other devices
• This causes network conflicts and connectivity issues
• VMs may lose network connectivity

Solutions

Option 1: DHCP Reservations (Recommended)

Configure your router to reserve specific IP addresses for the VMs' MAC addresses.

Steps:

1. Get VM MAC addresses from Proxmox
2. Log into your router's admin interface
3. Find DHCP Reservations / Static DHCP / IP Reservations
4. Reserve each IP for the corresponding MAC address

Get MAC addresses:

ssh root@192.168.1.206
for vmid in 100 101 102 103; do
  echo "VM $vmid:"
  qm config $vmid | grep net0 | grep -o 'virtio=[^,]*'
done

Example router configuration:

• VM 100 (cloudflare-tunnel): MAC BC:24:11:D9:F7:DE → Reserve 192.168.1.188
• VM 101 (k3s-master): MAC BC:24:11:C1:75:A2 → Reserve 192.168.1.60
• VM 102 (git-server): MAC BC:24:11:ED:A2:F8 → Reserve 192.168.1.121
• VM 103 (observability): MAC BC:24:11:9D:5F:E7 → Reserve 192.168.1.82

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Option 2: Exclude IPs from DHCP Pool

Configure your router's DHCP pool to exclude the static IP addresses.

Example:

• DHCP Pool: 192.168.1.100 - 192.168.1.254
• Excluded/Reserved: 192.168.1.1 - 192.168.1.99
• Static IPs: 192.168.1.188, 60, 70, 80 (within excluded range)

Router settings:

• DHCP Start: 192.168.1.100
• DHCP End: 192.168.1.254
• This leaves 192.168.1.1-99 for static assignments

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Option 3: Use NAT Network (Best for Isolation)

Use a separate NAT network for VMs, completely isolated from the main network.

Benefits:

• No IP conflicts (VMs on private network 10.0.0.0/24)
• Network isolation
• Access via Proxmox host (port forwarding)
• Router DHCP unaffected

Implementation:

• Run: ./scripts/fix/setup-nat-with-ssh-keys.sh
• VMs get IPs: 10.0.0.10, 10.0.0.11, 10.0.0.12, 10.0.0.13
• Access via: ssh -p 2222 ubuntu@192.168.1.206 (VM 100)

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Option 4: Use DHCP with Cloud-Init

Let VMs get IPs from DHCP, then discover them via QEMU Guest Agent.

Benefits:

• No IP conflicts
• No router configuration needed
• IPs discovered dynamically

Implementation:

• Remove ipconfig0 from VM config
• Let cloud-init use DHCP
• Use QEMU Guest Agent to discover IPs
• Scripts already support this via get_vm_ip_from_guest_agent()

Note: This is what the guest-agent IP discovery pattern supports!

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Current Configuration

Your VMs are currently configured with static IPs:

• VM 100: 192.168.1.188
• VM 101: 192.168.1.60
• VM 102: 192.168.1.121
• VM 103: 192.168.1.82

Risk: If your router's DHCP pool includes these IPs, conflicts will occur.

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Recommended Approach

For Production/Stable Setup:

Use Option 1 (DHCP Reservations) - Best of both worlds:

• Static IPs for VMs (predictable)
• Router manages IP assignments (no conflicts)
• Works with existing network setup

For Development/Isolation:

Use Option 3 (NAT Network) - Complete isolation:

• No router configuration needed
• VMs isolated from main network
• Access via Proxmox host

For Maximum Flexibility:

Use Option 4 (DHCP + Guest Agent) - Dynamic discovery:

• No static IP configuration
• No router configuration
• IPs discovered automatically
• Works with existing scripts

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Quick Fix Script

I can create a script to:

1. Check if IPs are in router's DHCP pool
2. Switch VMs to DHCP mode
3. Use guest-agent IP discovery
4. Update all scripts to use discovered IPs

This would be the most flexible solution and works with your existing guest-agent IP discovery pattern.