Situation, I'm replacing 3 stacked Catalyst 3750s as my core with stacked MS390s. I have the 390s stacked, firmware updated and online. I'll be changing them out next week on our shutdown week. I'm pre-configuring as much as I can, without creating IP conflicts.
My existing catalyst has a default gateway of 10.10.23.254 (IPs changed to protect the innocent) and a route of 0.0.0.0 0.0.0.0 10.10.23.254 configured. In addition, vlan interfaces are configured (vlan20 - management vlan 10.10.20.1, vlan 60 - voice 10.10.60.1, etc) with helper-address 10.10.20.50 for DHCP requests.
When I look at creating the first L3 interface on my 390 stack, I get confused. I've got
Subnet - "10.10.20.0/22"
Interface IP - <This is my question> 10.40.20.1?
Default Gateway - 10.10.23.254
Multicast - Disabled
VLAN - 20?
Then, I create my other interfaces.
Name - Voice
Subnet - 10.10.60.0/22
Interface IP - 10.10.60.1
VLAN - 60
Multicast - Disabled
Client addressing - Relay to another Server
DHCP Server IPs - 10.10.20.50
I may have answered my own question typing this out. lol
Creating the initial default gateway also creates the interface for my vlan 20 (with IP 1010.20.1), correct? Then I don't need to create vlan20 in later steps.
To start using layer 3 routing, navigate to the switch details page by going toSwitch > Monitor > Switchesand clicking on the switch to be configured. Under Status > L3 routing status, clickConfigure layer 3 settings.
The window that appears will allow the configuring of the first routed interface and a default route. It is recommended that the uplink VLAN be configured first
The default route will be pointing to the default gateway adress of you first interface
Ugh, yeah, my bad. I meant 10.10.20.1. Yes, that is currently in use at my core. Thanks.
Okay, so that confirms my understanding. I see where it says that now in the documentation. Guess I glazed over that.
Next question is a chicken/egg situation.
If I configure the interfaces on the Meraki stack while online, there will be IP conflicts with the existing Cisco stack. I can configure them offline, but then if I take the Cisco stack out and replace it with the Meraki, it will not be able to get to the cloud to update the config since the Cisco is the gateway.
I suppose at cutover time I bring the Meraki online, let them update the config and have conflicts, then take the Cisco stack down and make the change over. Right?
I'm not familiar with MS390, but with all the other MS switches ...
The ultimate default gateway is usually a firewall or some path to the Internet. You need to put the switch management IP addresses all in this same VLAN, and the default route for them needs to point to that firewall. They CAN NOT point to any L3 interface on the switch itself. The switch management system does not use the primary routing table.
As you mentioned, it won't be able to get its config as it would need its config to get to the Internet.
Then you create the layer 3 interfaces. These are separate different IP addresses from the management interfaces. And these have their own [primary] routing table.
Whether this also applies to the MS390 I don't know.