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Forum Discussion
RBR 750 wrong subnet mask
My Orbi RBR 750 WAN setting says my subnet mask is 255.255.252.0
Yet my ISP modem says 255.255.255.0
on ipconfig/all its 255.255.255.0
Why? will this be a problem and how do i change it on the router?
Jimmy
9 Replies
What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Be sure your using a good quality LAN cable between the modem and router. CAT6A STP is recommended.The RBR auto detects what ever comes from the ISP only. If the ISP is putting out 255.255.252.0 then they will need to make the change from there side.
Also IPCONFIG /All only shows subnet mask on what's used on the LAN side.
Firmware Version
V7.2.6.21_5.0.20XB7 Arris modem
Cat 6 cables
Those modems are typically built with a router with in. This would be a double NAT (two router) condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only 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
Try option #2 first...
JN_AB wrote:
My Orbi RBR 750 WAN setting says my subnet mask is 255.255.252.0
Yet my ISP modem says 255.255.255.0
on ipconfig/all its 255.255.255.0
This may reflect different "views" of IP subnets.
If is clear that on a Windows computer, ipconfig /all reports the subnet mask that was told to the computer when the DHCP process assigned network information to the computer:
- IP address for the computer
- Subnet mask for the computer (which is almost always 255.255.255.0)
- Gateway IP address (which is the IP address of the LAN port of the device which responded to the DHCP request)
If the Orbi is in router mode, then the default for the Orbi is to use 255.255.255.0 for the LAN. - DNS Server (which is also the IP of the LAN port of the device which responded to the DHCP request, e.g. the Orbi)
The Orbi router reports the information that was given to it from the device which responded to its DHCP request for information. In this case, it appears that the ISP has communicated a public IP address (rather than a private one) and is using a subnet mask of 255.255.252.0 (indicating that more than 253 customers are on the ISP network connecting to this server.
What the ISP router is reporting is unclear. For example, when the Arris XB7 combination modem/router/WiFi device is in router mode, it almost certainly assigns subnet masks of 255.255.255.0 when it responds to DHCP requests. When the Arris is in Bridge Mode, it should not respond to DHCP requests. However, just as the Orbi router does not erase information in the LAN setup table when put into Access Point (AP) mode, maybe the XB7 also "remembers" its LAN setup information in case the user changes it back to router mode. In that case, the XB7 could be reporting, "if you put me back into router mode, I will use DHCP to give devices IPs in a certain LAN subnet, tell them the subnet is 255.255.255.0, and tell them to use ME for the gateway and DNS resolver.
In other words, there may be nothing wrong at all.
