I have two routers connected together via ethernet cable to provide better WiFi coverage over my house. I have two Mac desktop computers connected via ethernet to the primary router, and various wireless devices in the house such as phones and tablets typically access the Internet via the second router's WiFi.
Everything works fine, except that when these wireless devices are uploading data (such as when lots of photographs or videos are taken on a mobile phone, and Android sync uploads them to Google), then the Internet connection on my desktop computers becomes very slow: instead of webpages loading more-or-less instantly, all webpages now take 30 or 40 seconds to load. Even a simple webpage like the Google homepage can take over 30 seconds to load.
This slowdown only happens when data is being uploaded on the second router. It does not occur if data is downloaded. And it does not really occur if the wireless devices are uploading data through the WiFi of my primary router, only when they upload data through the second router. It also occurs in various browsers (Safari, Firefox, Chrome).
My primary router is a BT Home Hub 5, and the second router is a Netgear DGN3500. I have also used a Netgear WNDR3400 as the second router and had the same problem. This slowdown problem occurs whether I connect the routers together by LAN-to-LAN, or by LAN-to-WAN (on the WNDR3400).
In the dual router setup I have, the 2nd router has its DHCP server turned off, and both routers have their own unique LAN IP numbers on the same LAN network. The 2nd router has its gateway address set to the LAN IP of the primary router.
My Internet connection is via ADSL2+, but I have a pretty good download speed of around 20 Mbps.
Any suggestions as to what might be causing this page load slowdown, and what might be done to rectify it, are gratefully received.
EDIT: thanks to the help and suggestions of Appleoddity below, I realized this slowdown problem was actually occurring when uploading data on either router's WiFi, and this appears to be more of an issue connected to the asymmetric upload/download speeds of ADSL, rather than related to the fact that I have two routers connected.