The 2511 should have a ethernet interface, "interface Ethernet0
ip address x.x.x.x 255.255.255.0
no mop enabled"
But in the box, I only see Console and AUX port? No ethernet?
Any idea? How can I connect to this box through LAN ?
When you say, "in the box" I assume you mean you're looking at the physical chassis. The ethernet interface is there. It's an AUI interface (http://www.cisco.com/en/US/products/hw/routers/ps214/products_tech_note09186a00801f5d86.shtml). You will need an ethernet trasceiver to convert the AUI interface to something more modern (i.e. RJ45).