Three ways an ISP hands your router a connection
When you plug a new router into a fiber ONT or a VDSL line, it has to identify itself the way the ISP expects. There are three common patterns, and they can be combined. With DHCP (also called IPoE or automatic IP), the router just asks for an address. With PPPoE, the router logs in with a username and password before it gets an address. With VLAN tagging, the router labels every frame with a number the ISP's network expects, and traffic without that label is not carried.
The three ISPs below show how different the answers can be, even within one country or one ISP. The examples are not ranked. They show why the only reliable source is your own ISP's settings page for your exact service. [1][2][3]
| ISP and service | Connection type | VLAN | Credentials | Source |
|---|---|---|---|---|
| Aussie Broadband (Australia), nbn FTTP, FTTC, HFC, Fixed Wireless | Dynamic, IPoE or DHCP | Tagging disabled (enter -1 if a value is required) | None needed | [1] |
| Zen (UK), FTTC/SoGEA/VDSL | PPPoE | 101 | PPP username and password | [2] |
| Zen (UK), Full Fibre | PPPoE | N/A | PPP username and password | [2] |
| Zen (UK), CityFibre | PPPoE | 911 | PPP username and password | [2] |
| CenturyLink (US), own modem | PPPoE credentials supplied on request | Must support VLAN tagging 201 | Get them from CenturyLink chat | [3] |
PPPoE in plain terms
PPPoE runs the old dial-up PPP login over Ethernet. RFC 2516, the standard that defines it, describes a discovery stage. The router broadcasts a request (PADI). Access concentrators at the ISP answer with offers (PADO). The router picks one and asks for a session (PADR), and the ISP confirms it (PADS). Only then does the login happen. [4]
Two practical consequences follow. A wrong password or a missing VLAN tag usually shows up as no session at all, rather than a slow connection. And the PPPoE wrapper takes up room in every packet. RFC 2516 says the PPP MTU must not exceed 1492, because Ethernet carries 1,500 bytes and PPPoE adds a 6-byte header and a 2-byte protocol ID. [4]
VLAN IDs: the label the ISP expects
A VLAN ID is a number from the ISP's network design, not something you choose. Zen's table shows that one ISP can use different IDs on different access networks: 101 on FTTC, 911 on CityFibre and none on Full Fibre. CenturyLink states plainly that a third-party modem must support VLAN tagging 201. [2][3]
Getting the VLAN wrong is the classic reason a correct PPPoE password still fails. If your ISP lists a VLAN, set it. If it says tagging is disabled, as Aussie Broadband does, leave the field empty. Aussie Broadband says to enter -1 if the router insists on a value. [1]
Where GL.iNet puts the PPPoE, VLAN and MTU fields
In the GL.iNet admin panel, go to INTERNET, then Ethernet, and click Modify. The protocol options are DHCP (the default), Static and PPPoE. GL.iNet notes that ISPs typically supply the username and password used for PPPoE. [5]
The VLAN ID and MTU fields live under Advanced, and they apply to all three protocols. GL.iNet says the VLAN ID is required only if the provider's server needs the interface to use a specific tagged VLAN ID. It lists the default MTU as 1500 bytes. On a PPPoE connection, that is above the 1492 ceiling RFC 2516 sets for PPP. If your ISP publishes an MTU, enter it. If it does not, 1492 is the standard's limit. [5][4]
Before cutover, you can type the PPPoE details into the new router, save them and leave it unplugged. When you move the cable from the old router, the new one only has to connect, not be configured under time pressure.
| Setting | GL.iNet location | What to enter |
|---|---|---|
| Protocol | INTERNET > Ethernet > Modify | DHCP, Static or PPPoE, as your ISP specifies [5] |
| PPPoE username and password | Same screen when PPPoE is selected | Exactly as the ISP issued them [5] |
| VLAN ID | Advanced | Only if the ISP lists one, for example 101 or 911 on Zen [5][2] |
| MTU | Advanced (default 1500) | ISP's figure; no more than 1492 for PPPoE per RFC 2516 [5][4] |
Questions to ask your ISP before cutover
Ask these in one support chat and save the answers. Each one maps to a field on the router or to a support limitation you should know about before you change anything.
- Is my service DHCP/IPoE, PPPoE or Static, and on which physical port (ONT Ethernet or DSL)?
- What VLAN ID, if any, must my router tag? Does it change by access network, as Zen's does? [2]
- What are my PPPoE username and password, and how do I reset them? CenturyLink issues them over chat. [3]
- Is there a required MTU? If there is not, plan for 1492 on PPPoE. [4]
- Do I keep a phone line on the ISP's router? If so, will it work when that router is removed or bypassed?
- What support do I lose with my own equipment? CenturyLink limits technical support and will not install service with non-CenturyLink equipment. [3]
- Does the ISP need a MAC address or device registration? Aussie Broadband explicitly says not to clone the MAC address. [1]
When it still will not connect
Work from the bottom up. First confirm the cable is in the router's WAN port and the ONT or modem shows a link. Then check the VLAN: a missing or wrong tag usually means no PPPoE offer at all. Next, retype the PPPoE password, since a single wrong character fails silently. Last, look at the MTU. If some websites load and others stall, a too-large MTU is a common suspect on PPPoE, and 1492 is the figure to try. [4][5]
Keep the old router boxed and labelled until the new one has run for a few days. Putting it back is the fastest rollback if the ISP turns out to need a setting you were not told about.
Questions before you decide
Where do I find my PPPoE username and password?
From your ISP, not from the router. CenturyLink says to chat with it to get the PPPoE username and password for a third-party modem. Zen links to a separate page for finding connection details for home and business customers. Some ISPs, such as Aussie Broadband on nbn, need no username or password at all.
What MTU should I use with PPPoE?
RFC 2516, which defines PPPoE, says the PPP MTU must not be greater than 1492. That is the 1,500-byte Ethernet payload minus a 6-byte PPPoE header and a 2-byte PPP protocol ID. GL.iNet's Ethernet page lists 1500 bytes as the default MTU, so use the figure your ISP gives you, or 1492 if it gives none.
Do I need a VLAN ID for every fiber connection?
No. Zen lists no VLAN for its Full Fibre service but VLAN 911 for CityFibre and 101 for FTTC. Aussie Broadband tells customers to disable VLAN tagging on all its nbn types. GL.iNet's docs say the VLAN ID field is only needed if the provider requires a specific tagged VLAN.
Will my ISP support a router I bought myself?
Often only partly. CenturyLink says you will receive limited technical support for service issues related to a third-party modem, that it is not covered by the equipment replacement program, and that technicians cannot install service using non-CenturyLink equipment.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- Aussie Broadband: BYO router settings, nbn guide Accessed 30 Oct 2026
- Zen Internet: General settings for a non-Zen router Accessed 30 Oct 2026
- CenturyLink: Third-party modem support and settings Accessed 30 Oct 2026
- RFC 2516: A Method for Transmitting PPP Over Ethernet (PPPoE) Accessed 30 Oct 2026
- GL.iNet Router Docs 4: Ethernet (internet) Accessed 30 Oct 2026
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