Correct process to switch uplink ports for new ISP interface

[dales]

We currently have a handful of MS-120 switches (using L3 switching) in the field that need the uplinks reconfigured for a new Internet provider. Currently, port 1 on the MS is acting as an uplink port for the existing provider. We would like to connect the new provider on another port (port3) and swap over to that new port once it's verified working, with a minimum of downtime to our customers. Both uplink connections require different static IP addresses. I am looking for a known procedure to make this change happen remotely via the dashboard. So ... a few questions...

Can I have more than one uplink live at the same time ?

Can I connect the new link to the switch and verify its operation without taking the old uplink down?

If the answers to the above questions are yes, can I then just change the default route on the L3 page of the dashboard to point to the new provider instead of the old provider and see virtually no downtime?

Or does this change require someone to be physically at the location to config the local dashboard?

Any help would be appreciated

[cmr]

@dales the MS-120 switches are L2 switches, they don't do L3 routing.  Do you have a diagram of your setup as something else must be terminating the ISP connection.

[dales]

My bad cmr the core switch is an MS-250 and the access switches are MS-120's

[dales]

[cmr]

@dales I'm confused, is the MS250 connected directly to the internet without a firewall, or does the ISP provide that?  If it does, does the new ISP provide a firewall?

Also looking at the IP addresses you have the 201.17.173.248/29 subnet on the left, but the devices on the right have addresses in the 201.17.251.x range, is that a mistake?

It does look like you are using public IP addresses for the switch management ports, do you have more public IP addresses for the devices or are they using private IPs and if so how are they NATed?

[dales]

Thanks again for your help cmr!!

The ISP is doing firewall services at the provider edge, and has given us a /29 to use on the "management network" for equipment addresses, and a different /23 of public addresses for clients. This setup has been in place for many years, and was recently reconfigured using a  Meraki solution so that we can manage it from the cloud

[cmr]

@dales If the provider supplies the IP addresses then presumably the new provider will be supplying a new range or ranges of IP addresses, or do the addresses actually belong to you?

If the former then as you aren't using NAT or presumably DHCP, you'll need downtime to change all the hosts to the new IP addresses, but you could do it one by one if you create a new VLAN for the new subnet, trunk it between the switches and have an access port on the 250 where you plug in the new ISPs firewall.

What is the new ISP giving you in terms of public subnets?

[dales]

Those public IP's for the clients are ours and will not change