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Forum Discussion
Orbi + Comcast cable modem in Bridge Mode
I have a Comcast/XFinity Cable Modem. It's only connection is an Orbi (Netgear) mesh wifi device. I am trying to set up DDNS. While I have a good high level understanding I don't have enough to sort this one out.
1. When I am configuring DDNS, does the Cable Modem (Switch) have the public network IP or does is it the Wifi Router?
2. It seems from the ORBI/Netgear admin UI that they insist that I have only one of Netgear, No-Ip or Dyn.com. I have a namecheap name and I wanted to create a subdomain from that name to my DDNS name but I am a little stumped.
https://i.stack.imgur.com/sxKNG.png
Thanks!
7 Replies
The goal is to have the Orbi be "the router", and thus have the public IP address. The Comcast unit needs to be in "bridge" or "passthrough" mode.
Netgear is pretty clear that only those choices for DDNS will work. If someone has found a way to make a different DDNS service work, I hope they will post instructions.
Good Luck
Thanks... that's kind of what I believed. But when I did that all kinds of odd things were happened (cause and effect not fully established though :) On the other hand when it is not in bridge mode everything seems to work fine, i.e. having two routers is not breaking anything I can notice.
I don't just want to get it to work, I'd like to understand what's going on!
My Orbi ran as a router behind another router for two years, and I was perfectly happy. However, I never attempted to set up things like port forwarding, VPN, etc. Netgear ships the Orbi with router as the default and thousands of customers happily plug them into "whatever they already have" from their ISP. If it wouldn't work at all, there would be mass hysteria. On the other hand, those thousands of customers seldom attempt things like running their own web servers, wanting to access security cameras in a way different than the camera people intend, connecting from far away, etc.
The key to all this is Netword Address Translation (NAT). The ISP sees only one IP address (the "public" one). Every packet comes from that address, but from a different "port". The NAT part of the router keeps track of which port belongs to which device on the back side. So, when a packet comes back addressed to that port, the IP address is translated to the private IP address, the port number is translated, and the packet delivered. For very simple things, "double NAT" causes no problems, but for anything complicated it causes horrible problems.
There are some great articles on the web about "double NAT and why it is a problem".
Modem Combo Units:
This would be a double NAT condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop
