All devices on the network (including Orbi) shows no internet connection except for one wired imac?

[groupjdesign]

I'm having a weird issue, I lose intertnet access throughout my whole wired  & wireless network (including the RBR50 showing a magenta ring and listed) except for one imac which retains its connection to the internet. I'm typing this on that machine right now. There are two imacs, two macpros, two printers, three NAS devices & an apple tv connected via ethernet with a GS724Tv4. There are usually 5 - 10 wireless devices connected depending on who's home. The internet is comcast business through a SMC modem which connects to the RBR50 which connects to the switch. The Orbi is in router mode but receives the connection from the cable modem through DHCP. When the last comacst tech was here we could not get the Orbi connected when the SMC was in bridge mode.

Shutting down the cable modem & then rebooting Orbi usually does the trick in the past but it has gone out several times in the last few days. When this started happening earlier in the year I stopped using the Comcast DNS servers & when to google's. that kept the magenta ring away until just recently. The thing that is throwing me is the one imac with internet. It's not consistant, there are times where it does lose internet connection, but usually when that happens, the internet is restored before I need to restart anything. 

Any thoughts on why the one wired imac remains connected? I feel that this is key to figuring out what is going on. I'm taking everything down tonight  ( including the switch) & seeing where I'm at in the morning. I usually keep everything going 24/7, maybe everything just needs a good rest & restart.

Thanks!

PS - should I be using the GS724Tv4 switch for the routing instead of the orbi?

[FURRYe38]

Other users are reporting issues of problems with Managed switches. I've asked for this information and have found that Managed switch have been causing problems with the Orbi systems in between the router and satellite(s), or a combination of what ever is in the orbi FW and managed switches are not liking each other. One user mentioned that he disabled IGMP protocols on his switch, then his system began to work. Something you can try your self and see. I would get a NON-Managed switch and put in place instead of the managed switch to see if you still exhibit problems. I use NON-Managed switches here and haven't seen any issues with my system since day one.

Let us know what you find out...