ASUS RT-N600 not coming online

[bbxrider]

so this an old router, I used it 2017-2018 and 2018-2019 with 2 different modems
connected to comcast xfinity accounts and it worked ok. now have a new xfinity account, performance+,
using a net gear A500 modem and it won't connect, e.g. come on line. A netgear AC750 router
works ok with the A500, so it appears the A500 modem is working ok. Comcast is no help as to why the
RT-N600 is not working, so hoping to get ssome help or ideas here. The RT-N600 dhcp's my pc and I
can log into it and all looks normal and ok like it used to when it worked with the previous modems and
comcast. just wanting to save a few bucks and use the RT-N600 over buying a new router,

 

[OzarkEdge]

so this an old router, I used it 2017-2018 and 2018-2019 with 2 different modems
connected to comcast xfinity accounts and it worked ok. now have a new xfinity account, performance+,
using a net gear A500 modem and it won't connect, e.g. come on line. A netgear AC750 router
works ok with the A500, so it appears the A500 modem is working ok. Comcast is no help as to why the
RT-N600 is not working, so hoping to get ssome help or ideas here. The RT-N600 dhcp's my pc and I
can log into it and all looks normal and ok like it used to when it worked with the previous modems and
comcast. just wanting to save a few bucks and use the RT-N600 over buying a new router,

When you test with the Netgear router, are you using the same WAN cable as with the N600? Try a different trusted WAN cable anyway.

OE

 

[bbxrider]

thanks for the reply, trying new cable led to a solution. turns out the N600 has a new modem setup program, 'quick internet setup', which I ran with the new cable, it does a discovery thing where you power down the modem and its waiting for the power up and with that I connected all good with the new cable, after that I substituted the original cable and that now works as well. It kept all the previous use setup info, like 2.4 and 5g names, passwords, etc. I don't remember using the quick setup in the past but for sure it got the comms going this time.

 

[KsWoodsMan]

Initially your RT-N600 router and the ISP gateway probably were both configured to use the same subnet.

The ISP gateway might have been using 192.168.1.254/24 for it's IP address and handing out DHCP allocation in that subnet.
And the RT-N600 router was set to 192.168.1.1/24 and also handing out DHCP addresses in the same subnet.
This doesn't work for a cascaded NAT router setup.

Sounds like you found it with the Quick Internet Setup.
It's routines check the WAN IP address given by the ISP gateway and correct this problem by changing the router subnet to 192.168.2.1/24 .