Adding L3 switch in site and need to change ip address remotely

[hmc250000]

We are adding a L3 switch in a site.  The ISP WAN router was routing for the site.  We would like to reassign the ISP router's ip address to a new vlan interface on our L3 switch so we don't have to change the gateway of the client machines. We have no remote hands support for the site. What is the proper way of changing the ip address remotely so we don't loose connectivity?

[PhilipDAth]

I'm going to guess the ISP router had a private IP address on it's inside.

The question then will be how does the site now get Internet access.  Steps I can think of are:

• Change the switches management interface configuration so that it is pointing at the new Internet circuit.  It should come back online in the dashboard after this.  You should see it checking in from the new public IP address.
• If their is an exsting L3 interface on the switch and default route, update that to point to the new Internet circuit.
• Turn off the old ISP router.
• Create the new VLAN to take over the old ISPs LAN details.

[hmc250000]

Change the switches management interface configuration so that it is pointing at the new Internet circuit. It should come back online in the dashboard after this. You should see it checking in from the new public IP address.

Can we change the ip address of the switch after the ISP router's ip address has changed? How will the switch access the internet after the IP change on the ISP router? 

Can I change the switch it's management ip locally from the LAN? This is in case I can get access to a machine on the local LAN.

[cmr]

Are the client machines not using DHCP, if not could they?  If they could then you can simply assign the L3 switch an IP in the same range as the ISP device's IP and set the default route to the ISP device's IP address.  Once this is done simply change the default gateway given out by DHCP to that of the switch L3 interface.