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cisco router configuration for Ethernet over Copper.

Need help configuring Cisco 1841 router and firewall.

My provider has put their equipment and given me 2 subnets with public ip address. I am used to getting just one Subnet and connecting my firewall straight to the hand off. But in this case I am a bit confused. I assume I will need to put a router and configure it with before I connect my firewall.

Configure 1841 with:
Subnet 1:
First usable ip:

Subnet 2:
ISP says that they route this network via 200.xxx.67.204

I also have a firewall that I would like to be on the subnet 2 at 20.xxx.97.130 and have my private network 192.168.xxx.xxx behind it.

Thank you for all the help.

What make / model is this firewall you're talking about mike2002 ?

This is also HIGHLY dependent what exactly you want to do. If you only have one cable coming off the ISP-supplied
equipment and/or want a single chain of devices from the ISP-supplied equipment, then you could configure a
secondary ip address on the 1841 as follows :

config t
ip address x.x.x.x [subnet mask here]
ip address y.y.y.y [subnet mask here] secondary

If the ISP-supplied equipment allowed it, or you didn't mind the setup, you could connect a layer2 switch
and have the 1841 take the /29 subnet while your firewall did the /25.

My 00000010bits


Raleigh, NC
He cannot do that since the second subnet is aimed at 204 -- the firewall would have to be 204 to get that traffic.


reply to mike2002
If they routed the second subnet to the X.X.X.204 address, then assign to the wan interface on your 1841 (lets use fastE0/0). For the other subnet, assign 20.xxx.97.129 to the other interface on your router (lets use fastE0/1). Connect your firewall to the the FastE0/1 and assign it an IP address out of the second subnet. Configure your firewall.


reply to mike2002
It's a little odd that they give you a /29 with a gateway of 201 but your first usable is 204. Your first usable should be 202. Perhaps this is a shared circuit with other people in your building?

You have the option of setting your firewall up with single IP of and ignoring the /25 or using the /25 without the 1841. If that's the case and you don't need or will use the /25 return it to the ISP.

If you need or must use the 1841 you can use it as follows:

interface FastEthernet0/0
description metro-e circuit id carrier tmc phone number
ip address
duplex full
speed 100
no cdp enable
interface FastEthernet0/1
description Customer Network
ip address 200.xxx.97.129
no cdp enable

ip route name default-route-to-isp-a

Then connect your firewall to FA0/1 and use 209.xxx.97.130 as the address or you have the option of subnetting the 209.xxx.97.128/25 further by adding vlans or routes to other networks you may need.
I do not, have not, and will not work for AT&T/Comcast/Verizon/Charter or similar sized company.