Xfinity w Netgear CM500V modem and Synology RT2600ac router: no internet

[keema_t]

Comcast/xfinity is my ISP. In August I replaced the comcast combo modem/router with a Netgear CM500V modem and a Synology RT2600ac router, plus another Synology MR2200ac router downstream to extend the range. This has worked great for the last 3ish months, then this week the internet connection started to get intermittent, then dropped completely. 

When I connect a pc directly to the modem, the internet connection is still great, with DL speeds around 300Mbps. But when I connect the router downstream, there is no internet connection. I tried both routers independently to see if one was 'broken', and reset everything to factory defaults, but still had the same results: internet connection on the modem but it doesn't extend to the router. The router page indicates status of GOOD for both phone and router. 

Is this a modem setting, or something on the router?  I thought this modem was certified by Xfinity, and it has worked great until now (and appears to still work great, at least when I connect to it directly).  The router has been fine too, no issues until this week. 

I saw a similar post recently by @ERS1961 , and it was solved by replacing the router with a rental unit from Comcast. I can try this, but the point of using the CM500V was so I wouldn't have to monthly pay the rental fee. 

[keema_t]

An update: I got a modem/router from Xfinity this morning. Both wired and wifi connections work fine. I changed the configuration on the Synology router so it is a WAP only, and it works fine, again solid internet connection via both wifi or ethernet (and wifi from Synology as WAP is set as unique, to clarify that network connection is coming from that router).

I then set the Xfinity modem/router up in bridge mode, so it acts more like a modem only. I put the Synology router back into router mode, and the internet connection is fine via ethernet/wifi connections through the Synology.

This sounds to me like the problem is with the Netgear modem, but I still don't understand what the problem is. I can live with this setup (keeping and using the Xfinity hardware), but not my first choice. 

[darkangelic]

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@keema_t wrote:

This sounds to me like the problem is with the Netgear modem, but I still don't understand what the problem is.

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Doubtful, as you connected a PC directly to the CM500V and it worked just fine.

I suspect it was a configuration issue with the Synology RT2600 AC router (or perhaps a double NAT issue or similar with the MR2600AC) , as you probably reset it to change it to AP mode and then back to router mode. 

As the RT2600AC functions as a router again,  I suspect that if you put the CM500V back in service, it'll be OK now. 

[keema_t]

I can try it again, but one of the steps I initially took was to reset the RT2600ac to factory default settings, and make sure it was workng as a router. I confirmed all these settings with the onboard router access page. When it didn't work with the RT2600ac, I went through the same steps with the MR2200c, and same effect. When I first got the Xfinity modem/router, I first verifed that it worked in router mode, and set hte RT2600ac as an AP, and that worked.  Then I set the Xfinity units up as a bridge, and put the RT2600ac back into router mode, and it still worked. 

I've talked to both Netgear and Synology, and both think their products are working fine, and suggested that a change from the ISP (provisioning maybe?) caused this issue. 

Any other tests that you can suggest? 

[darkangelic]

Have you been restarting both the modem and the routers every time the connection is changed?