NOt knowing what the premise is behind the IRB on other location, I can only explain what IRB is. as name suggests it's "integrated routing and bridging". to put it simply, you have a router with say two ethernet interfaces, you connected end hosts on this two interfaces and you want these hosts to be in the same subnet/broadcast domain. Here is a dilemna because the router's interface are L3 and you must put an IP address on them but putting an ip address on each interface would put the host in different subnet. Hence the solution is to bridge them so the two hosts are in the same subnet and same broadcast domain but wait the hosts would also like to be able to talk L3 or to other subnet via IP, for that it needs a L3 interface so they can be routed but where would you put the ip address? hence the IRB, you bridge the lan interface and create logical interface in router called interface BVI, this is the routed interface for those hosts on the bridge interfaces, now you have hosts in the same subnet and they can talk to other subnet too via l3 interface called BVI. Now, for the 3560, this is a L3 capable switch. which means it's a switch but it can route. now, this switch can do better than the routers IRB, for one thing switch have more interfaces than the router which means you can connect many hosts as much as port available. going back to bridge concept, the switch have vlan concept where you create a vlan then assign port to a particular vlan and then create an SVI (logical interface called interface vlan x), this is your L3 interface, this is where the hosts gateway would normally point to. oh, to answer your question 3560 does NOT support IRB, it doe snot need to since it can do vlans. feel free to ask what ever confuses you on my explanation.
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