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Can't get DHCP IP on WAN LAN1 interface

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Silem2013
Star II

‎08-17-2025 11:49 PM

I have a weird issue - I have 2 ISPs that I want to use for failover.  I set WAN and LAN1 interfaces for Dual WAN but my LAN1 basically doesn't work - it shows "Your ISP's DHCP does not function properly" error.  I can switch ISPs around and each of them work on WAN port but not on LAN1.  To make matters worse the DHCP server from ISP on LAN1 can talk to my internal network causing rogue DHCP server issues.

My router is RT-AX3000 on 3.0.0.4.388_25210 firmware.  The setup used to work, I only noticed DHCP and failover related issues this year.

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Silem2013
Star II

‎08-20-2025 09:48 PM

Status update: disabling guest network and restarting the router fixes the issue. 

It really looks like having Dual WAN and guest network doesn't work together for RT-AX3000. 

It's quite an exotic combination but I hope it's fixable - dual WAN failover is really nice for working from home and guest network is good for ... house guests, obviously.  Now I just have to figure out some Wireguard VPN issues.

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Silem2013
Star II

‎08-18-2025 12:58 AM

This is strange.  I downgraded the firmware to November 2024, uploaded known good configuration that I created 3 months ago after a factory reset (I still had weird issues with one of the providers, but it could be ISP's finicky modem), upgraded the firmware to current and now it works.  No rogue DHCP servers and both connections get correct IPs.  I didn't test failover but it looks good.  In the end my uneducated guess is that the bug is somewhere in the settings that do not appear in Admin's front end and probably set by automatic security settings update?  I don't know, will wait for it to fail again and will just upload the configuration.  

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Alex52
Rising Star II
In response to Silem2013

‎08-18-2025 11:05 AM

It has been noted by ASUS that you may need to change some setup settings or possibly contact your ISP. Try changing the default WAN aggressive setting to continuous.

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Silem2013
Star II
In response to Alex52

‎08-20-2025 09:31 AM

Tried that, no change.  It's really not an ISP issue as outside DHCP should not propagate into the inside network. 

I think I found a way to replicate it - it works correctly after configuration restore but as soon as I enable a guest WiFi a rogue DHCP pops up in my main network.

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jzchen
Zen Master II
In response to Silem2013

‎08-19-2025 05:05 AM

At some point ASUS started enforcing the requirement that the type of connection between the two "WAN" has to be different type of physical port.  So in this case they both can not be the same, WAN WAN or LAN LAN, one must be WAN and the other LAN.  BUT you already mentioned that one is WAN, and the other LAN.  

https://www.asus.com/support/faq/1011719/

If both ISPs provide unlimited data (at no extra cost) you might consider Dual WAN load balancing?

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