[shb]

Am using Australian NBN internet (FTTC) with own Router for last 2 years. It has been working perfectly in that time. The Router I was using was non dd-wrt, model = Gateway F@st 5355.

To set up that Router, took just 5 minutes only. Like this: "Internet Settings", set "ipv4" to DHCP , and "ipv6" to off. Then configure the wifi SSID and password – and thats it. Then just plugged the ethernet cable from the NBN into the F@st5355n WAN port, and it worked. .

Within a few days I must return that F@st5355 Router.

Luckily, I have my rock-solid Linksys WRT1900ACSv2 to replace it with 😁💪
First, I upgraded my Linksys to r51306 (01/15/23).

Using factory default settings. Only changed passwords and added new SSID names. I also set to "Automatic DHCP" to get the address (from upstream, eg NBN).

Step 1 – I moved all (20-30 wifi and 2 ethernet) devices across to the Linksys.
Step 2 – Cable from Linksys WAN port to one of the F@st5355 LAN ethernet ports (while it remained connected to the NBN via its WAN port)..

This step was only to confirm the Router config was working, before removing the F@st5355 Router.

AND EVERYTHING WAS WORKING. – all devices could access internet ( via LinkSys -> F@st 5355 -> NBN ) . The Linksys was correctly being assigned an IP address (from F@st5355 Router ) thanks to the magic of DHCP.

Step 3 (final step) – Power off the F@st5355, and move the NBN ethernet cable from the F@st5355 WAN port to the Linksys WAN port.... and reboot the various components.

PROBLEM — the Linksys DOES NOT get any IP address the upstream NBN box (going into its WAN port). When the F@st5355 is the upstream box (from Linksys WAN port) – in that case it DOES get the ip address. However, when the NBN box is upstream, in that case it DOES NOT get an IP address.... YET, when the F@st5355 Router is in same position it DOES get an IP address.

What am I missing here ???

Is IPoE ever so subtly or slightly different to DHCP ?
Why would a dhcp address be assigned when the Router is F@st5355, but not when it is a DD-WRT router ???

Could the dd-wrt code to handle DHCP Client be working in some circumstances, but not all circumstances ??

[egc]

Your F@st5355 is probably on another subnet (Local Ip Address) as your Linksys.

Maybe the Linksys subnet is the same as your modem?

Try setting the same subnet as your F@st5355.

Furthermore you provider can track MAC address, usually if you unplug your router and you reboot your modem, wait 10 minutes and then plug in your router and reboot the router it could work, alternatively clone MAC address.

But it is possible that a slightly different DHCPC client is used which needs other vendor class specific settings but that is beyond my pay grade

[shb]

Hi @egc thanks for your thought !

I found out the answer. Problem is fixed.

All I needed to do was the WAIT until the F@st5355 lease expired ( 1 hour ) . Then the NBN correctly passed the IP address to a different device, other than the F@st5355. So there was NO PROBLEM and NO BUG about this in the dd-wrt code.

So my steps were - just power off the F@st5355 router for an hour - then attach the cable to the WAN port of my dd-wrt Router. Then dd-wrt Router does receive the IP address, subnet and gateway - as it should.