PPPoE
Alright, let's pull back the curtain on PPPoE—the protocol that lets your dusty DSL modem or fiber ONU talk to the Big Wide World of the Internet using nothing but a username, password, and your ISP's blessing.
💽 What is PPPoE?
PPPoE stands for Point-to-Point Protocol over Ethernet. It’s like wrapping an old-school dial-up handshake inside a slick Ethernet jacket.
- PPP (Point-to-Point Protocol): Originally used in dial-up over serial lines. Handles authentication, encryption, and IP address assignment.
- Ethernet: Your local LAN transport.
- PPPoE is the hybrid child—PPP running over Ethernet, allowing your ISP to treat you like a dial-up client even though you're using modern cables.
🌐 Why Does PPPoE Exist?
Because back in the early 2000s, telecoms were like:
“Wait, we can resell bandwidth per user by authenticating and tracking them individually? Sign us up!”
So instead of just plugging into the internet and getting a DHCP lease, you log in to your ISP like it’s 2004 MSN Messenger.
🧪 How It Works – The PPPoE Lifecycle
- Discovery Phase (PPPoE Active Discovery):
- Your router/modem sends a PPPoE Discovery Initiation (PADI) broadcast to find any ISP access concentrators.
- The ISP replies with PADO (Offer), and then your device picks one.
- After a handshake, both agree on a session ID.
- Session Phase (PPP over Ethernet):
- Now PPP starts. This is where your device sends the username and password (usually in PAP or CHAP format).
- If valid, the ISP:
- Authenticates you
- Assigns you an IP address (via IPCP, part of PPP)
- Routes your traffic to the Internet
- 🎉 You are online!
- All your packets are encapsulated inside PPP frames, which are further stuffed into Ethernet frames.
- Your ISP now knows exactly which account is using which bandwidth.
🔐 Username/Password: The Gatekeeper
This isn’t just a login—it’s your authentication token. It allows ISPs to:
- Identify the customer (per session)
- Throttle or limit bandwidth
- Track usage or apply billing
- Apply NAT or IP assignments tied to your account
Lose this, and you’re basically talking to the void. No IP, no packets, no memes.
🛠️ Why Use PPPoE Today?
- Legacy DSL systems still rely on it.
- Some FTTH ISPs (e.g., certain Asian and European markets) use it for:
- Per-user traffic tracking
- Built-in firewall rules
- VLAN tagging (often with VLAN ID 100 or 500)
⚠️ Limitations
- PPPoE adds overhead: 8 bytes per packet, which affects MTU. That's why PPPoE users often have MTU = 1492 instead of the usual 1500.
- Not as efficient as DHCP + VLAN + AAA setups used by modern fiber ISPs.
💡 TL;DR
| Element | Description |
|---|---|
| Protocol | PPPoE (PPP over Ethernet) |
| Auth Mechanism | Username & Password (via PAP/CHAP) |
| Assigned By ISP | IP Address, DNS, Gateway |
| Use Case | DSL, Fiber, situations where per-user auth is needed |
| Alternatives | DHCP with 802.1X / Radius / MAC binding |
MoNoRi-Chan would say:
“So you’re telling me I’m renting bandwidth I already paid for... using a 1990s login system... and they still throttle me? Sounds like Late-Stage Telecom™.”
Want to see a real packet capture or router config that handles PPPoE?
