Cisco router connection to ISP modem/router

skhirbash · ‎04-14-2008

We recently got a new DSL line from an ISP and were provided with a modem/router. In order to implement a controlled connection (content filtering, we decided to setup a Cisco router and link it the the ISP's router. Could someone provide me with a guide on how to accomplish this configuration?

Thanks in advance,

sK

graemeporter · ‎04-14-2008

Hi there,

You need to connect your Cisco router to your ISP router, and your switches to your Cisco router's other interface.

On the interface that faces your network (the Inside interface), assign an IP address from that subnet. Configure your host PCs to use your Cisco routers' Inside interface IP address as their default gateway.

On the interface that faces your ISP-provided DSL router (the Outside interface), assign an IP address from the subnet used on the ISP device's inside interface (this is almost always an RFC-1918 address, ie 10.x.x.x, 172.17.x.x or 192.168.x.x). Assign the default route for your Cisco router to be the IP address of the ISP-provided DSL router.

What you do next depends on what kind of site this will be.

If you're planning on using your Cisco router as a VPN device to connect this site to the rest of a larger network, then you should begin your VPN tunnel configuration.

If this site is all you have, then you will want to configure NAT Overload so that your PCs can access the Internet. You will also need to configure a route on your ISP's router to allow inbound (return) traffic to reach your subnet via your Cisco router.

This is a rather general guide, and I hope this is of some help to you. If you need more help, don't hesitate to ask.

Kind regards,

Graeme

commchf123 · ‎11-06-2019

We have a Business Account with our ISP because of our address. We've never used the public address block we have because we simply needed internet and a home wifi router works fine.

Recently I was testing something and plugged an Cisco 2911 ISR into the ISP modem with DHCP turned on the ISP facing interface. The interface received one of the public addresses but I had no internet connectivity (Unreachable responses from the ISP's CM IP address space). My guess is it's because there is no BGP setup and I would need to have the ISP give me that info.

Is this correct?

m.rana.ku · ‎04-15-2020

I am sharing a great content which will demonstrate step by step process of Connecting Cisco 2851 Router and Cisco 3560 Switch to ISP Home router and Configuring Cisco Router using Putty and finally Accessing Internet from Laptop and Desktop PC through this network.

https://youtu.be/rRgdlhSbczU