Cisco 871 Router: Quickly Change the ISP

Putty into the 871 Router

Run the command “Show Run” to start scrolling through and get the outside IP Interface, IP Address and Subnet Mask.

interface FastEthernet4
ip address %CurrentIPAddress% %CurrentIPSubnet%
!

Scroll further and get the IP Route (Gateway Address)

ip route 0.0.0.0 0.0.0.0 %CurrentGatewayIP%

Prpare a short script to remove the old ISP settings and add the new ISP settings.
Start with the Gateway (IP ROUTE).
Example below between the hypens.e

no ip route 0.0.0.0 0.0.0.0 %CurrentGatewayIP%
ip route 0.0.0.0 0.0.0.0 %NewGatewayIP%

interface FastEthernet4
no ip address %CurrentIPAddress%  %CurrentIPSubnet%
ip address %NewIPAddress% %NewIpAddressSubnet%
!
Run the command “Conf T

Copy and paste entire script into Putty.

Once internet is verified up and running, “Exit” out of Config mode.

Run the command “Write Mem

3 Comments

  1. I had dhcp server in my lan network.i want to intoduce the cisco-871 router without configure local dhcp server.what will be the configuration for dhcp in the 871 rtr such that laptop take the ip from my existing dhcp server

    1. Apologies for the delay, I didn’t see this comment before. Hopefully you got everything all figured out.

      You should be able to disable DHCP on the 871 and give it a static IP and make it your Gateway Address on your DHCP server.

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