# DHCP Migration: pfv-netboot → pfv-netinfra-01/02

**Date:** 2026-07-29
**Status:** ✅ **COMPLETE** — both servers in `normal` failover state, 333
active leases load-balanced. Netboot DHCP stopped + disabled.

> **Safety nets:** pfv-netboot, pfv-netinfra-01/02, sectestbed-sandbox, and
> ultix-streaming all have static IPs (reachable via Tailscale even if DHCP
> fails). sectestbed-sandbox snapshot `pre-dhcp-migration` exists as rollback.

## Migration results (2026-07-29 17:20 CDT)

| Check | Result |
|-------|--------|
| netinfra-01 (primary) | `active`, failover `normal`, 244 active leases |
| netinfra-02 (secondary) | `active`, failover `normal`, 89 active leases |
| Failover partnership | "Both servers normal" — load-balanced at split=128 |
| DHCP test (sandbox) | Lease obtained from 192.168.3.252, IP 192.168.3.50/22 |
| DNS handed out | `192.168.3.252, 192.168.3.253` (netinfra pair) |
| NTP handed out | `192.168.3.252, 192.168.3.253` (netinfra pair) |
| Domain | `knel.net` |
| Gateway | `192.168.3.254` |
| Webmin | Port 10000 (SSL) on both nodes; DHCP module configured |
| Netboot DHCP | Stopped + disabled (won't start on reboot) |
| Netmask fix | Both nodes corrected /24 → /22 |

## 1. Current state (discovered 2026-07-29)

| | pfv-netboot (SOURCE) | pfv-netinfra-01 (TARGET primary) | pfv-netinfra-02 (TARGET secondary) |
|---|---|---|---|
| IP | 192.168.3.250/22 | 192.168.3.252/24 | 192.168.3.253/24 |
| isc-dhcp-server | 4.4.3, **active** | NOT installed | NOT installed |
| Webmin | 2.652 (port 10000, SSL) | NOT installed | NOT installed |
| DHCP leases | **532 active** | — | — |
| DHCP config | `/etc/dhcp/dhcpd.conf` | — | — |

**Source DHCP config summary:**
- Subnet: `192.168.0.0/22` (covers .0.x/.1.x/.2.x/.3.x)
- Pool range: `192.168.0.1 — 192.168.3.200`
- Router/GW: `192.168.3.254`
- DNS: `192.168.3.250` (netboot itself — **changing to 252/253**)
- Domain: `knel.net`
- Lease times: 600s default, 7200s max
- DDNS: `ddns-update-style none` (globally disabled)
- ~37 host reservations (MAC → fixed IP)
- 3 global-scope host declarations (outside subnet)

## 2. What changes in the migrated config

| Setting | Old (netboot) | New (netinfra) | Why |
|---------|--------------|----------------|-----|
| DNS servers handed out | `192.168.3.250` | `192.168.3.252, 192.168.3.253` | Point clients at the netinfra Pi-hole pair (netboot will be decommissioned) |
| Failover | none (single server) | ISC DHCP failover-peer | Primary/secondary HA |
| DHCP interface | `eth0` | `ens18` | Different NIC name on netinfra VMs |
| Netmask on servers | /22 | **fix to /22** (currently /24) | Match the /22 network |

Everything else (subnet, pool range, reservations, lease times, domain) stays
identical. The host reservation list is copied verbatim.

## 3. Configs prepared

| File | Destination |
|------|-------------|
| [`dhcp/dhcpd-primary.conf`](dhcp/dhcpd-primary.conf) | `/etc/dhcp/dhcpd.conf` on netinfra-01 |
| [`dhcp/dhcpd-secondary.conf`](dhcp/dhcpd-secondary.conf) | `/etc/dhcp/dhcpd.conf` on netinfra-02 |

Both are identical except for the `failover peer` block (primary vs secondary).

## 4. Execution sequence

### Phase 1 — pre-flight (non-disruptive)

1. **Snapshot sectestbed-sandbox** (VMID 6000 on tsys5) — rollback point
2. **Fix netmask** on netinfra-01/02: `/24` → `/22` in `/etc/network/interfaces`
   (then `ifdown ens18 && ifup ens18`, or `systemctl restart networking`)
3. Verify Tailscale still reachable after netmask change

### Phase 2 — install prerequisites (non-disruptive, nothing serving yet)

On **both** netinfra-01 and netinfra-02:
1. `apt-get update && apt-get install -y isc-dhcp-server`
2. Install Webmin via official setup script
3. Copy `dhcpd-{primary,secondary}.conf` → `/etc/dhcp/dhcpd.conf`
4. Write `/etc/default/isc-dhcp-server` with `INTERFACESv4="ens18"`
5. Syntax check: `dhcpd -t -cf /etc/dhcp/dhcpd.conf`
6. **Do NOT start the DHCP service yet**

### Phase 3 — cutover (the critical moment)

**Goal:** minimize the DHCP gap. Existing clients hold valid leases for 600
seconds — they won't notice a brief outage.

1. **Stop netboot DHCP:** `ssh netboot 'sudo systemctl stop isc-dhcp-server'`
2. **Immediately start netinfra-01:** `systemctl start isc-dhcp-server`
3. **Immediately start netinfra-02:** `systemctl start isc-dhcp-server`
4. **Verify failover partnership:** check `journalctl -u isc-dhcp-server` on both
   — look for "failover peer pfv-dhcp: I move from recover to recover-done"
5. Wait ~10 seconds for lease sync

### Phase 4 — test

1. On sectestbed-sandbox: edit `/etc/network/interfaces` to DHCP
2. `dhclient -r` (release) then `dhclient` (request new lease)
3. Verify IP assigned, correct DNS, correct gateway
4. If fails: `qm rollback 6000 <snapshot>` and debug
5. If succeeds: change back to static (sandbox's normal config)

### Phase 5 — cleanup

1. **Disable netboot DHCP:** `ssh netboot 'sudo systemctl disable isc-dhcp-server'`
2. Verify Webmin DHCP module visible at `https://192.168.3.252:10000`
3. Document + commit

## 5. Failover mechanics (reference)

ISC DHCP failover uses a TCP connection on port **647** between the two servers.

- **Primary** owns the pool initially and can assign new leases immediately.
- **Secondary** enters `recover` state, syncs the lease database from primary,
  then transitions to `recover-done` → `normal`.
- If primary dies, secondary continues serving after the MCLT timeout (600s).
- If secondary dies, primary continues serving alone.
- **split 128** = load balance 50/50 (primary handles even hashes, secondary odd).
- Host reservations (fixed-address) are NOT subject to failover — both servers
  can independently assign reserved IPs.
