L3 routing setup

[JICSupport]

I've tried to figure out the L3 routing config on my own, but it's just not clicking in my head.  Most of the help leads to the same Meraki documentation page (https://documentation.meraki.com/MS/Layer_3_Switching/MS_Layer_3_Switching_and_Routing) and I guess I need it spelled out a little more, or explained differently. 

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

Name- "Uplink"

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

etc.

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. 

[ww]

Interface IP - <This is my question> 10.40.20.1?  I supose you mean 10.10.20.1 but thats currently in use at your core.

That is a ip thats not in subnet 10.10.20.0/22

https://documentation.meraki.com/MS/Layer_3_Switching/MS_Layer_3_Switching_and_Routing#Initializing_...

To start using layer 3 routing, navigate to the switch details page by going to Switch > Monitor > Switches and clicking on the switch to be configured. Under Status > L3 routing status, click Configure 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

[JICSupport]

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?

[PhilipDAth]

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.

[tkovac]

@PhilipDAth so are we putting the same gateway for all of the interfaces?

e.g. I have 10 x VLANs I need to create but the switches will be getting their internet access from an ISP router.

Do I point them all to the router?

[PhilipDAth]

For the switch management - yes.

[tkovac]

Thank you.