I am in the process of replacing our Linksys commercial router with a RB1100Hx2. We have a small software development business with around ~15 developers/users and wanted to start upgrading our internal network infrastructure for expansion.
I am having issues where the download rate from our ISP drops dramatically from 90Mbps to ~30Mbps when I switch out our current router with the RB1100Hx2.
Simple diagram of network for clarity: http://i.imgur.com/LbLqlZA.png
The RB1100Hx2 is configured as follows, at the moment it is not much because I am trying to narrow down the issue with having simple configuration.
Port 1 - DHCP Server (connected to the switch in the diagram)
Port 2 - DHCP Client (connected to the ISP Modem in the diagram)
Port 3-5 - Configured to have Port 1 as a master.
NAT rule - standard src-nat masquerade
At first, I thought it might have been the limitation of our old switch, but I find it odd that the Linksys can handle it just fine. It is also worth noting that if directly connected to the RB1100Hx2 (either Port 1 or its slaves) there is no issue.
I am looking for any suggestions, nudges in the right direction or perhaps a straight “you’re doing it wrong, you should be doing this” 
Thank you for your time.
What speed is the link between the 1100 and the switch? Is speed/duplex hard coded on either side or auto-negotiated? Check to ensure there isn’t a duplex mismatch which can result in one side falling back to half-duplex. This is more common in 100 Mbps links as the fallback for Gigabit Ethernet is full duplex when auto-negotiation isn’t detected on the other end of the link.
Thank you for your response, my apologies for getting back to you so late.
The link between the 1100 and the switch is auto-negotiated and currently saying it is 100Mbps (as expected) and full duplex.
Might be worth noting that I have also tried a different 10/100 switch and am able to reproduce the problem. My guess is a configuration setting I am missing, but I don’t know enough to take a guess at what it could be.
Does anyone else have any idea on what it could be? Is there any specific checks I can perform or tools within RouterOS that I should be using to diagnose what is happening?
We discovered a solution this morning by plugging in a small gigabit switch we had laying around. We placed it between the RB1100Hx2 and a 10/100 switch and we started getting expected internet speeds. My problem is “solved” but I am very curious in learning about what might have been going on between the RB1100Hx2 and the 10/100 switch.
