1721 with switch wic question

Got a 1721 with a 4 port fastethernet switch wic card. Pretty sure everything is working from a hardware perspective, but I am a bit confused about the router/switch interface.

When a router and switch are in separate boxes and the router is connected to the switch, you go into the router and configure the switch-connected port with an ip address.

With the 1721 and switch, I am trying to figure out how to configure the interface that goes from the router to the switch. My best guess right now is that vlan 1 is the router side of the switch, as all I have is the fastethernet0 on the 1721, and FA1-4 on the switch side.

Reviewed the documentation for the switch wic, but not quite getting it.

These integrated routers can be confusing. I finally figured out my 831 router, but that had an internal ethernet device that connected, in a virtual manner, the router and switch.

Thanks for any suggestions.

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Comments

Mark Knutson

It just occurred to me, if the 1721 can treat a vlan as a router destination, I could set this up to have 4 separate output destinations, one for each switch port.

Or is this like a layer 3 switch when the wic card is added--I have documentation on how to configure those. Then with the proper interface commends I could set a switchport to be switch or router.

networker050184

When you use the switch modules its connected to the router automatically. You don't need a special link with those older ones.

mikej412

4-Port Ethernet Switch Configuration Notes for the Cisco 1700 Series Routers [Cisco 1700 Series Modular Access Routers] - Cisco Systems

If you're just using it as a 4 port switch, create an SVI (interface vlan 1) and use that for the default gateway for the devices plugged into the switchports.

If you want the ports to act as separate/additional Ethernet Interfaces for the router, you put each port in its own VLAN and create an SVI for each VLAN (with the interface vlan xxx command).

fly351

phoeneous wrote: »

Sounds like you are interested in doing router on a stick.

Hmm with a HWIC-4ESW.. wouldn't the WIC be running CEF and support SVI's? That is, replicating L3 switching on the WIC? I have no experience with these so I am not sure to be honest, just my understanding

fly351

blah, Mike beat me to it lol

Mark Knutson

phoeneous wrote: »

Huh? When you say "boxes" are you referring to the module slots or physically seperate router and switch? ...

Physically separate, just to explain how one gives ports on a router ip addresses--and thereby create directly connected networks in the routing table, but not necessary for a switch.

Mark Knutson

mikej412 wrote: »

4-Port Ethernet Switch Configuration Notes for the Cisco 1700 Series Routers [Cisco 1700 Series Modular Access Routers] - Cisco Systems

If you're just using it as a 4 port switch, create an SVI (interface vlan 1) and use that for the default gateway for the devices plugged into the switchports.

If you want the ports to act as separate/additional Ethernet Interfaces for the router, you put each port in its own VLAN and create an SVI for each VLAN (with the interface vlan xxx command).

I have read that document, and it is an extremely cool and large document for a wic card--and the wic card as a switch has a lot of configuration options.

I think I understand your explanation, but to be sure.... Lets say I make FA0 192.168.1.1/24. Now I want stuff plugged into the switch (FA1-4 on the 1721) to be on network 192.168.2.0/24, and have the router consider that network directly connected, arp, and forward packets accordingly.

So, if I set up vlan 1 with an svi on 192.168.2.1/24, then the router will consider the switch directly connected to 192.168.2.0/24 and so on? Then the anser to my question would be that the router can 'see' the wic switches vlans, and they take the role that a physical interface like a wic eth card would play.

Is that correct?

Mark Knutson

It just occurred to me, what if the wic turned the whole 1721 into a three layer switch with ports fa0-4 being essentially part of that switch--as opposed to a router with a switch one one end. That would be too cool.

Though I am able to configure and ping from fa0 already, so maybe not.

Reviewing 3 layer switch info now.

I am guessing a lot because the 1721 is at home and I am at work.

fly351

Mark Knutson wrote: »

It just occurred to me, what if the wic turned the whole 1721 into a three layer switch with ports fa0-4 being essentially part of that switch--as opposed to a router with a switch one one end. That would be too cool.

Though I am able to configure and ping from fa0 already, so maybe not.

Reviewing 3 layer switch info now.

I am guessing a lot because the 1721 is at home and I am at work.

That would be virtually impossible (pun intended lol) since switches perform *most* of their switching functions in hardware and only send complex tasks to the L3 engine. The WIC its self would pretty much be considered a MLS, but not the whole router.

tiersten

As this is a WIC-4ESW and the 1700s don't support HWICs, you're going to be limited in throughput as the speed of the WIC slot itself is low. It won't matter too much for a lab but in a production environment it will.

mikej412

Mark Knutson wrote: »

It just occurred to me, what if the wic turned the whole 1721 into a three layer switch with ports fa0-4 being essentially part of that switch--as opposed to a router with a switch one one end. That would be too cool.

The WIC-4ESW is a little layer 2 switch -- which can gain the layer 3 function via the host 1721 router.

Put each ESW port in a separate VLAN and create an SVI for each VLAN on the router and you have a 4 port layer 3 switch (which doesn't have all the switch capabilities that a real switch would have -- the unsupported stuff is listed in the link I posted) that also knows how to reach the network out the Router's FA0 port. Or you have a Router with 5 FastEthernet ports that would choke under any heavy load between the attached networks (as tiersten pointed out the throughput issue).

Mark Knutson

Thanks, all. I believe I know enough to proceed with configuration now.

I do have a 3550 if I need performance, but the 1721 is just a component of an educational lab.

fly351

tiersten wrote: »

As this is a WIC-4ESW and the 1700s don't support HWICs, you're going to be limited in throughput as the speed of the WIC slot itself is low. It won't matter too much for a lab but in a production environment it will.

You smart person you...