🧠 Fedora MAC Address Randomization — Troubleshooting Log

Context:
While connecting from g16 (Kubuntu) to e14 (Fedora) via SSH,
the e14 host became unreachable at its usual IP (192.168.1.12).
Investigation revealed Fedora’s default MAC randomization caused a new IP (192.168.1.15)
to be assigned, breaking router DHCP binding and SSH connectivity.

---

🧩 1. Symptoms

Command	Result	Interpretation
ping e14 (from g16)	Destination Host Unreachable	No route to previous IP
nslookup e14	192.168.1.12	Name resolution still cached
ssh leo@e14	No route to host	TCP unreachable
ip addr show wlp3s0 (on e14)	link/ether 0a:8c:57:a9:8b:ad permaddr aa:aa:aa:aa:aa:aaf	Randomized MAC detected

Root Cause:
Fedora’s NetworkManager uses a randomized Wi-Fi MAC address each connection
(wifi.cloned-mac-address=random), invalidating the router’s static IP binding.

---

⚙️ 2. Corrective Actions

Step 1 — Disable Random MAC for the Wi-Fi Connection

nmcli connection show
sudo nmcli connection modify "<SSID>" 802-11-wireless.cloned-mac-address permanent
sudo nmcli connection down "<SSID>"
sudo nmcli connection up "<SSID>"
````

Verify:

```bash
ip link show wlp3s0

✅ You should now see the hardware MAC.

---

Step 2 — Optional Global Policy (for all Wi-Fi)

Create /etc/NetworkManager/conf.d/10-disable-wifi-random.conf:

[device]
wifi.scan-rand-mac-address=no

[connection]
wifi.cloned-mac-address=permanent

Reload:

sudo systemctl restart NetworkManager

---

Step 3 — Restore Router Binding

On your router, bind:

aa:aa:aa:aa:aa:aa → 192.168.1.12

This ensures the IP stays fixed across reboots and OS reinstalls.

---

🧰 3. Verification Script: check-mac.sh

A utility script to verify if Fedora is still using a randomized MAC.

#!/usr/bin/env bash
iface="${1:-wlp3s0}"

if ! ip link show "$iface" &>/dev/null; then
  echo "❌ Interface '$iface' not found."; exit 1; fi

active_mac=$(ip -o link show "$iface" | awk '{print $17}')
perm_mac=$(ip -o link show "$iface" | grep -o 'permaddr [0-9a-f:]*' | awk '{print $2}')
[ -z "$perm_mac" ] && perm_mac=$(sudo ethtool -P "$iface" 2>/dev/null | awk '{print $3}')

echo "🧠 Interface:  $iface"
echo "🔹 Active MAC: $active_mac"
echo "🔸 Permanent:  $perm_mac"

if [ "$active_mac" != "$perm_mac" ]; then
  echo "🚨 Warning: active MAC differs — randomization is still active!"
  echo "👉 Run: nmcli connection modify \"<SSID>\" 802-11-wireless.cloned-mac-address permanent"
else
  echo "✅ OK: active MAC matches hardware MAC."
fi

---

🔍 4. Verification Flow

Step	Command	Expected Result
Check MACs	check-mac.sh wlp3s0	Same active/permanent MAC
Router lease	grep e14 /var/lib/dhcp/dhclient*.lease	Confirms 192.168.1.12
Ping test	ping -c 4 e14	Replies successfully
SSH test	ssh leo@e14	Connects without issue

---

💡 Reflection (Lyceum Notes)

• Material Cause (M): Fedora Wi-Fi hardware with MAC randomization feature
• Formal Cause (F): NetworkManager configuration rules and router DHCP bindings
• Efficient Cause (E): Fedora default privacy setting altering MAC per session
• Final Cause (T): Restoring network stability and predictable SSH routing

Observation: Modern OS defaults emphasize privacy (randomized MACs) over LAN persistence. In controlled lab environments like the Lyceum Home Lab, predictability outweighs anonymity — thus disabling MAC randomization aligns with system telos: “stable reflective connectivity.”

---

✅ Outcome:

• e14 now consistently reports its hardware MAC.
• Router rebinds static IP 192.168.1.12.
• g16 ↔ e14 SSH restored.
• Verified using check-mac.sh.

---