VMID and IP Allocation

This page explains how go-pve-qemu picks a free VMID when an install request omits id, and how that VMID decides the VM's IP.

VMID to IP Mapping

GATEWAY = 192.168.0.1
VMID    = 120
IP      = 192.168.0.120/24   (first three octets of GATEWAY + VMID)

Because the last IP octet is the VMID, VMIDs must fall within 100–254: below 100 is reserved by Proxmox, above 254 is not a valid host address.

Probe Range

Variable	Default	Correction
`ASSIGN_IP_START`	`100`	`0` or < 100 → 100
`ASSIGN_IP_END`	`254`	`0` or > 254 → 254

A reversed range is swapped automatically.

Two-Ended Concurrent Probe

Each round spawns one goroutine for start and one for end, then moves start++ and end-- until the two meet. A semaphore of size 10 caps concurrent probes.

Each candidate VMID is checked in order and dropped on the first hit:

Order	Check	A hit means
1	`/etc/pve/nodes/*/qemu-server/<vmid>.conf` exists	Some node already has this VMID
2	`qm config <vmid>` succeeds	Proxmox knows this VMID
3	`192.168.0.<vmid>:22` accepts a connection within 2 seconds	A host already uses that IP

The first VMID that passes all three is sent to the result channel, and every unfinished probe is cancelled.

Results and Limits

Case	Result
Free VMID found	Used as the VMID and last IP octet
Every VMID taken	`cannot find available IP`
No result within 10 seconds	`timeout: no available IP found`

Because both ends are probed at once, the result is not guaranteed to be the lowest free number
Check 3 uses a fixed 192.168.0. prefix in the current code and does not follow GATEWAY; on a different subnet it probes the wrong host
An explicit id in the request skips every check