NM-4E or NM-16ESW

[rswilliams]

I need to add some Ethernet ports to a 3640, for new connections to a WAN provider. In looking at these two modules, it would seem either one could work, but the switch card is about half the cost. Why would 16 ports cost less than 4? Are there some constraints on the switch card that would prevent routing between different networks on individual Ethernet ports? For example, I just need to route from network 10.0.0.0/16 on port 1 to network 10.1.0.0/16 on port 2.

Thanks.

[darrenj]

I agree, it does seem strange that 4 x 10Mb ports are more expensive than 16 x 10/100Mb ports. Here is a link to the 'cheaper' NM-16ESW, you can view all the supported features to ensure it does all you want:

http://www.cisco.com/en/US/customer/products/hw/routers/ps274/products_data_sheet09186a0080088752.html

If all you are doing is the routing you describe above, I'm sure it will work.

[bcbvale]

The way I understand it is that the NM-16ESW does not privide routability between the ports on that module. In other words they will always be a part of the same network so in effect you are adding a layer 2 switch capability to your router on one logical port (16 physical ports). That to me explains the cost difference. Since the 16 ports are not routable, between each other that is, there is a limitation.

I've never used the module so I cannot be sure but that seems to be the case from what I've read.

ChrisV

[Prashanth Krishnappa]

It does support SVI and can route between VLANs. Each port cannot be a routed port and need to be assigned to a VLAN

[rswilliams]

Thanks everyone. If I followed this correctly, in order to route between ports on the switch, the ports would need to be in separate VLANs. So for instance if I put port 1 in VLAN 1 and port 2 in VLAN 2, the 3640 could route between VLAN 1 and VLAN 2. Compared to the NM-4E, it's some extra configuration steps to set up the single-port VLANs.

I'm not familiar with SVI yet, will take a look. Would a configuration like this introduce any performance hits? Are there issues with things like routing protocol support?

Thanks again.

[Prashanth Krishnappa]

SVI is Switch Virtual Interface. You'll need to create one VLAN interface for every VLAN to route between VLANs. The following page should help as well

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t11/ft1636nm.htm

I do not foresee any performance hits and we have lot of customers who are using it this way

The 4 port module is not a switch and cannot be assigned to a VLAN(you'll need to use bridge-groups instead)

[rswilliams]

Thanks!