Hello Miguel,
1) The 2911 has three on board ethernet interfaces; we have three VLANs and three internet connections, so we need to use HWICs to get three more ethernet ports. That's right?
Theoretically you could use additional VLANs even to substitute for WAN connections, plus the switch. You have three internal VLANs, plus you would have additional three VLANs, each for a separate internet connection. These VLANs would then be split at the switch. However, I admit that this solution would be quite clumsy albeit working. It depends on what additional money you can spend on buying an extension module for your 2911 router.
2) We need three HWICs or there is some kind of HWIC with more that one ethernet interface?
This is the list of available compatible modules:
http://www.cisco.com/en/US/products/ps10537/products_relevant_interfaces_and_modules.html
HWICs with routed ports are usually very expensive - buying three router HWIC port cards would in my opinion be similarly expensive to buying a switching module. If you decide to buy additional ports I would recommend purchasing a switching extension card instead - check out the EHWIC modules, not the SM ones - while the SM are more feature-rich, they are again more expensive as far as I know.
3) The routing solution is to assign static routes in the 2911 for each interface connected to a VLAN through a 2911's interface connected to internet?
No, this would not be sufficient because classic IP routing makes its decisions based exclusively on the destination, not on the source. What you want to do, though, is to take both source and destination into account when routing your packets. You would either need to use the Policy-Based Routing (PBR), or implement VRFs (separate routing tables) for each internal VLAN.
4) Simply connecting three different router interfaces with three different switch ports, each one of them assigned to one of the three different VLAN, are we going to get internet access for all devices in those VLANs? or do we need to configure something else like trunking, VSIs...?
If you connect individual router ports to individual switchports on a switch, with these switchports being in separate and distinct VLANs, the devices in these VLANs will be able to talk to the router, and if the routing has been set up properly, also access the internet. No trunks will be necessary here.
However, you could use trunking to actually save the ports on your router. If the aggregate traffic of all VLANs towards internet does not exceed 1 Gbps, I would recommend configuring subinterfaces on the router and using a single physical link to the switch, configured as a trunk. Using three physical ports on a router to access three VLANs on the switch is cumbersome and not really helpful.
5) Can we achieve our goals using the SG-200 switch?
I do not know the SG-200 but as long as it supports VLANs and 802.1Q trunking/VLAN tagging, it will work.
6) We have the chance to use older routers, is this possible? We're specially interested in knowing if a 1841 or a 2801 router could be used for this setup.
Yes, this would be possible with these routers as well. Note that the throughput of these routers is lower than the throughput of 2911. What is the expected aggregated flow size to/from the internet?
Best regards,
Peter
