2 WAN ports on the Cisco 891W

[RickS03]

Hi, I'm runnig a Cisco 891W: 

Cisco IOS Software, C890 Software (C890-UNIVERSALK9-M), Version 15.2(4)M6, RELEASE SOFTWARE (fc2)

ROM: System Bootstrap, Version 12.4(22r)YB3, RELEASE SOFTWARE (fc1)

Cisco 891 (MPC8300) processor (revision 1.0) with 498688K/25600K bytes of memory.
Processor board ID FTX183180PX

I've got two WAN ports (Gi0 and Fa8). I've got everything working on the Gi0 interface. 

I don't have any type of redundant network available. What can I do with Fa8? Can I reconfigure it to be an internal interface? Can I use it to be a connection to the WAN link?  Or without a redundant connection is there nothing I can use it for?

[Richard Burts · Accepted solution]

If you have a single connection to outside it would not make much sense to attempt to connect both interfaces to it. Just use Gi0 as your outside interface. I do not have much experience with the 891W but believe that the FastEthernet interfaces through Fa7 are set up as switch ports. You can use them as access ports or as trunk ports. It looks like Fa8 is probably not set up as a switch port. So I do not believe that you can use it in exactly the same way as your other Fa ports. Assuming that it is set up as a routed port I would think that you could connect a device to it, assuming that the device would be in a subnet that is different from the subnet used on the other Fa interfaces.

HTH

Rick

[RickS03]

Fa0-7 are switch ports. 

Gi0 is the external interface, and the device is definitely routing. 

However, if I hook a device to Fa8, it doesn't get an IP address from the internal DHCP (on device) or external DHCP (external network), and can't ping gateways or other systems  if I manually configure a IP for the internal or external subnet. 

I could use another port both internally and externally, so it'd be handy if there was some way to use it. 

[Richard Burts]

Unless you have configured a DHCP pool to use with it I would not expect a device connected to Fa8 to get an IP address using DHCP. What I was suggesting was something like this:

- configure an IP address on Fa8 that is different subnet from the other Fa interfaces. If the other Fa interfaces are 192168.0.0 then you might use 192.168.8.1 255.255.255.0 as the address on Fa8.

- connect a PC to Fa8.

- configure the PC as address 192.168.8.2, using mask of 255.255.255.0 and gateway of 192.168.8.1

- you would need to configure address translation for this subnet to be able to access the internet. If you are doing any kind of security policy or traffic filtering on the router for traffic from outside you would need to consider the new subnet in them.

This suggestion assumes that you would use Fa8 for additional inside connectivity. You could also use the interface for outside connectivity if you had a second outside connection that was Ethernet.

HTH

Rick

[RickS03]

I hadn't expected it to work with DHCP either, I just included that for completeness. That's why I also said what I'd tried with static addressing.

Yes, adding a new subnet to the interface, and a new static IP address to the laptop gives me a working network connection. That's perfect, as it gives me a network that's easy to identify, isolate, and firewall. 

thanks.

[Richard Burts]

Thanks for the update. And I do appreciate completeness, especially when trying to understand remotely what is happening.

It sounds like you are satisfied with what you have done on the router now. But I keep learning that lesson about making assumptions. So are you satisfied or are there other things you would like it to do? We could make Fa8 provide an IP to the laptop using DHCP. There are probably some other things that might be done if we knew what you want it to do.

HTH

Rick

[RickS03]

I think that does it. I know how to get DHCP and what not working. I just needed to understand that i could use that port in a non-redundant mode. BTW, you're correct, it doesn't support being in a vlan (which I think is what initially threw me). 

[Richard Burts]

Thanks for confirming that you are now satisfied with how the router is configured and running. I am glad that my explanation was helpful.

HTH

Rick

[Richard Burts]

It is good that you now have it working. The extra LAN interface can be helpful. Thank you for marking this question as solved. These forums are excellent places to ask questions and to learn more about networking. I hope to see you continue to be active in the forums.

HTH

Rick