KB 104

===How do I set up a Cisco 675 or 678 router to use a routed subnet (instead of NAT)?===

Article:104
Created:2002-07-16 18:02:51
Categories:
  routing
  DSL

Question or Symptom

How do I set up a Cisco 675 or 678 router to use a routed subnet (instead of NAT)?

Resolution

Once you flush the NVRAM, you will need to access the Cisco via a blue management cable connected to the serial port on your computer.

To set the unit up for PPP mode we first need to flush the NVRAM. Type the following:

       enable
       set nvram erase
       write
       reboot
 

This takes a minutes to reboot. Next we'll set up PPP. Use your email account login and password on the "login" and "password" lines.

       enable
       set ppp wan0-0 ipcp 0.0.0.0
       set ppp wan0-0 dns 0.0.0.0
       set ppp wan0-0 login Your_Email_Login
       set ppp wan0-0 password Your_Email_Login_Password
       set ppp restart enabled
       set dhcp server enabled
       set nat disable
       set interface vip0 ip <ethernet_ip_of_cisco>
       set interface vip0 mask <subnet_mask_of_cisco>
 

The "dhcp" lines are optional. Only use them if you want the Cisco 675 to be your DHCP server. If you have another DHCP server on your LAN or if you assign static IPs to your machines, then you don't need to set up DHCP.

       set dhcp server pool 0 ip <pool_start_addr>
       set dhcp server pool 0 netmask <pool_mask> 
       set dhcp server pool 0 gateway <ethernet_ip_of_cisco>
 

If you have a 678 and your DSL protocol is DMT instead of CAP (all new Qwest DSL circuits after April, 2001 are DMT), then you need to enter these additional commands:

   set interface wan0-0 disable
   set interface wan0-0 vpi 0
   set interface wan0-0 vci 32
   set interface wan0-0 enable
 

Next, save the new configuration and reboot the router:

       write 
       reboot
 

At this point any passwords you previously set will be gone, so you'll want to set a login and enable password. Please don't lose these!

        enable
        set password exec Your_Exec_Password
        set password enable Your_Enable_Password
        write
 

Here is a specific example of what the "interface" and "dhcp" lines might look like. This is assuming a subnet of 216.184.23.16/29, with IP address 216.184.23.17 assigned to the router, and addresses .18 through .22 assigned via DHCP:

       set interface vip0 ip 216.184.23.17
       set interface vip0 mask 255.255.255.248
       set dhcp server pool 0 ip 216.184.23.18
       set dhcp server pool 0 netmask 255.255.255.248
       set dhcp server pool 0 gateway 216.184.23.17

Related KB articles

 KB 81 How do I configure my Cisco 675 or 678 for Megabit service?

 KB 94 How does one set up port forwarding on the Cisco 675 router?

 KB 95 How does one change the internal IP address of the Cisco 675 router?