# WOL Outage Fix and Network Analysis Report (Including Test Results)

![2대의 서버간 패킷을 전달하는 트럭 이미지](/media/whitedec/blog_img/c5334f31e2784b2cb4cb3d038482f194.webp)

## 1. Overview {#sec-d90460152eb8}

- **Sender:** Raspberry Pi 5 (`192.168.0.xxx`)
- **Receiver:** RTX 2060 PC (`MAC: AB:CD:EF:GH:IJ:KL`, `IP: 192.168.0.xxx`)
- **Network change:**
  - **Normal:** Raspi and the 2060 PC were connected to the same router (Bridge B) in the same physical segment.
  - **Problem:** The 2060 PC was moved to the upper‑level router (A) directly, separating it from Bridge B.
- **Symptom:** The usual WOL command (`255.255.255.255`) no longer powers on the PC.

## 2. Symptoms {#sec-cd8bf7952942}
**Failing case:** `wakeonlan [MAC]` (Limited Broadcast)  
 
  - Destination: `255.255.255.255:9`  
  - Result: No response from the 2060 PC.

 **Successful case:** `wakeonlan -i 192.168.0.255 [MAC]` (Directed Broadcast)
 
  - Destination: `192.168.0.255:9`  
  - Result: **The 2060 PC powers on.**
## 3. Experiments and Verification {#sec-7ec2133bb210}

**✅ Experiment 1: Verify packet transmission from the sender (Raspi)**

- **Goal:** Rule out OS or software‑level transmission errors.
- **Method:** Monitor the interface with `tcpdump`.

```bash
# Raspi terminal
$ sudo tcpdump -ni eth0 udp port 9
19:25:35.861285 IP 192.168.0.xxx.52072 > 255.255.255.255.9: UDP, length 102
```

- **Conclusion:** The Raspi generates and sends the packet correctly.

**✅ Experiment 2: Check if the packet reaches the receiver (2060 PC)**

- **Goal:** Determine whether the TP‑Link bridge blocks the broadcast.
- **Method:** Run `tcpdump` on the 2060 PC while the Raspi sends the default command.

```Bash
# 2060 PC terminal (listening)
$ sudo tcpdump -ni enp5s0 udp port 9
listening on enp5s0...
# (Result: No packets captured)
```

- **Conclusion:** Packets addressed to `255.255.255.255` do not pass the Bridge B segment.

## 4. Root Cause {#sec-4f5ed2fec746}
image
The issue stems from the **broadcast scope** and the **forwarding policy of the bridge device**.

| **Type** | **Limited Broadcast (255.255.255.255)** | **Directed Broadcast (192.168.0.255)** |
|----------|------------------------------------------|------------------------------------------|
| **Meaning** | "Only within this physical link" | "The entire network that uses this IP range" |
| **Bridge behavior** | Treated as local traffic, not forwarded upstream. | Recognized as valid network traffic and forwarded. |
| **WOL outcome** | **Failed** – blocked at the network boundary. | **Successful** – reaches the 2060 PC via router A. |

## 5. Resolution {#sec-44b0bd17641a}

- **Fix:** Specify the subnet broadcast address with `-i 192.168.0.255`.
- **Convenience:** Add an alias to `.bashrc`.

```bash
alias wake2060='wakeonlan -i 192.168.0.255 ab:cd:ef:gh:ij:kl'
```

## 💡 Final Insight {#sec-9f6e065a5c79}

`255.255.255.255` is a **Local/Limited Broadcast**; it cannot cross physical network boundaries. In segmented environments (router‑level bridges, etc.), using a **targeted subnet broadcast (`192…255`)** provides reliable delivery.

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