Home router with NAT makes internet much slower than with bridged-IP

Question

I have a BeWAN iBox A5100 wireless router and a 100 Mbps direct internet connection (non-DSL). When I use the bridged IP option, speedtest.net reports downlink speed as 85mbps which is quite OK.

When I switch to NAT, the speed drops to 35mbps. The computer where I run the test is connected over 150 mbps WLAN and the rest of the setup is exactly the same. There are no other devices connected to the router. I tried switching between NAT and bridged IP a few times and the result is always the same. The problem with bridged IP is that my ISP provides a max of 4 public IPs which is not always enough for all connected devices.

My question is, is it some sort of known behavior that NAT is always slower, is it a problem with the router, or something else?

Answer 1

This is a common problem for many older (and perhaps some lower-end not-so-old) consumer routers. They simply lack the processing power to manage speeds above 20-30 Mbit, (so 35 is "pretty good in the affected class") presumably because they were built to a price point and with the expectation that 10MBit was a "fast" home connection when they were built, so the designers thought they were providing adequate headroom (or their corporate overlords did) within the budget constraints.

NAT is not always slower, but it does take more processing, so if the processor is not up to the task, it will be slower.