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I just bought a Cisco 3825 and a NME-16es-1g-P because I needed an extra gig port. What I didn't realize at the time was that this card has its own OS and routing engine, etc, so it can't be managed directly from the router's OS.

My question is this: I need the 3 gig ports, 2 native and one on the card, to connect to parts of our internal infrastructure.

Can I, and if so how, use one of the 16 Fa ports on the card to act as the WAN link instead of one of the gig ports? I know it's probably complicated, but it's the best I can come up with given the equipment available. The would have been easier if it was an ESW card, but such is not the case.

Could one of you awesome people give me a step by step guide in how to configure this so that it runs smoothly? I know Cisco commands etc, but this interaction between the two systems is a bit beyond my reach.

Thanks in advance!

I should be clear that I HAVE researched this for the better part of a week. I've read through this guide: https://www.cisco.com/c/en/us/support/docs/interfaces-modules/network-modules/82288-es-mod-config.html (and about a dozen others) And, while informative, it doesn't address the question I have.

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin ♦
    Feb 19, 2018 at 17:50

2 Answers 2

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What you got was a switch module for your router; it doesn't have its own routing engine because it doesn't do routing. The interfaces in this module are switch interfaces, and they cannot be used as router interfaces. It sounds like you need a WIC module with a 1 GB interface for your WAN connection. The WIC slots are for adding WAN connections.

You should use one of the interfaces built into the router as your WAN interface. You can use the interfaces in the switch module as if the router is a distribution switch, and trunk to other switches in your LAN.

What you need to do with the switch module is to create VLANs on your router, create SVIs to use the VLANs, and assign interfaces in the switch module to VLANs or trunks, just as if the router is a switch.

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  • I only need a single WAN connection, and as our WAN connection is only 100Mbps, I wanted to use a T100 port for that, while keeping the faster ports for interoffice traffic. Is that somethign that's possible? If not, what would I need in order to make it work?
    – Bruce
    Aug 7, 2017 at 20:35
  • You want a WAN interface to be a router interface, and this switch module doesn't have any router interfaces. For that, I suggested the WIC module, which would be a router interface. What you have is basically a 16-port switch connected to a virtual router interface.
    – Ron Maupin ♦
    Aug 7, 2017 at 20:37
  • Ok, it sounds like this router may not do what we need. Let's say that we forget the existing card for the moment. Are the two native gig ports good for anything other than a connection to the WAN Modem? In other words, can one of them be used to connect to a switch and have dhcp hand out IPs to any devices connected? Or would I need some other port type for that? If other port type, what card(s) would I need so that I could have minimum 3 gig links to the three parts of our network, all capable of handing out IPs from the same pool/subnet?
    – Bruce
    Aug 8, 2017 at 15:43
  • Yes, we use the built-in interfaces for the local LAN. The WIC slots are what are intended for WAN connections; after all, WIC stands for WAN Interface Card. You can get a variety of WICs, including gigabit ethernet.
    – Ron Maupin ♦
    Aug 8, 2017 at 15:45
  • Ok, again, if I need to have THREE gig ports for LAN connectivity, what should I be using? the NME i assume is LAN, since i can't imagine 16 WAN ports. And, can the 2 native gig ports be purposed as LAN connectivity?
    – Bruce
    Aug 9, 2017 at 2:13
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As long as you go down the VLAN/SVI path with that switching module, AND as long as you can get along with the restrictions they impose, you can use them for most purposes of routing.

A few things that don't work well (or at all) with the VLAN/Switchport/SVI combination, in no particular order:

  • no ingress QoS (no marking, queueing or anything). Marking/Classification of traffic can be done on the SVI, however.
  • no egress QoS I can think of
  • no subinterfaces (802.1q Trunks however are possible)
  • no rapid-spanning tree for the VLANs, portfast however is supported
  • NAT inside/outside should work alright - as long as you apply it to the SVI in question, of course
  • probably netflow and ip flow ingress/egress won't work on the switch ports, but might on the SVIs
  • IPsec termination won't work on the individual switch ports, but might on the SVIs
  • even if they are switch modules, they offer no support for (L2-)EtherChannel, IIRC.

Ron is right: The 16 ports on that module are not "proper" router interfaces. I think they were primarily intended for branch office use, where a second device (i.e. a separate LAN switch) was undesirable.

However, if you know what you're doing and why, they can be very useful, even as "cheap L3 interfaces".

Cheers Marc

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