Got called in to look at a very strange network the other day... They were running a business off a (A) Linksys E2500 home wireless router. Now off of this router is one cable going to a (B) Mako dual wan appliance, which then goes to a (C) Cybera appliance which hosts a VPN connection as well as a (D) Cisco RV042 router. Now the other cable off the original router goes to another (E) E2500 Linksys router which only has a laptop and provides wireless to a printer and cell phones for employees.
Now router (A) is controlling PPPoE from a bridged DSL modem. Router (A) IP is 192.168.1.1 and servicing everything via DHCP (This will change in near future). Router (E) acting as an access point is also LAN IP of 192.168.1.1 and handing out DHCP. The laptop connected to (E) also has a secondary NIC via USB that connects to some point in the other side of the network. The Mako fails over to secondary ISP (Cellular) after only a few minutes and generally won't return. I believe either the laptop router (E) is creating the problem. Router (A) is experiencing over 2,000ms latency and over 5% packet loss. So I removed router (A) and reconfigured the DSL modem to handle the PPPoE and this now becomes router (A) in the equation. This router is set to 192.168.0.1 and has around 25ms latency with less than 2% packets loss and everything works great! We are keeping an eye on this for a week or so, before any more changes are made.
Eventually the Mako should be the router and have multiple subnets, and the DSL modem will be a bridge again. Not worried about this part of the story.
My question refers to: "I believe either the laptop router (E) is creating the problem." Please make your argument as to what the problem was.