Hi,

I'm planing to purchase RB1100AHx2 and put it as a BGP router in a small datacenter. It will receive two upstream links: one of 10mbit/s and another with 1gbit/s. The official benchmarks (in the Routerboard.com page) says this model can reach up to 3gbit/s. But the benchmark was made using 4 ethernet ports simultaneously.

My question is: can I expect this routerboard model will reach a transfer rate in a single ethernet port close to the 1gbit/s speed I'm purchasing from my upstream provider?

In your case you are talking about real-Internet traffic, so average packet size will be closer to results of 512 byte packets - up to 2,3Gbps without contrack and up to 1,5Gbps with contrack.
And those results are without any configuration.

If you will use this RB1100Ahx2 without conntrack (no firewall, no ppp, no queues) and use ports ether1-11 - there should be no problems to get 1Gbps.

Thanks for your reply but my question remains: the benchmarks were made using 4 ethernet ports simultaneously. Will I reach 1gbit/s in a single ethernet port, the port that will connect my router to my upstream?

I think you misunderstand what "test with four ports" means. Yes! Of course you will get 1Gbps per port. If you can get 1GBps per port when four ports are loaded, you can potentially get more when only one port is loaded (as CPU has more time for it).