Layer 3 Routing

[Ben]

Hi All,

So i'm configuring L3 routing on my network and wanted to check if i'm right. 

I have my following setup

MX250 - Corestack MS410 - Serverstack MS250

MX and MS410 have a 10.0.18.0/24 network for going towards the internet MX = 10.0.18.1, This created a default route 0.0.0.0/0 towards 10.0.18.1

The MS410 have the L3 interfaces but now i want to route 10.162.128.0/17 to IP 10.162.128.1 (Alcatel L3 switch of 3rd party here in the building) 

That alcatel switch is in Port 1 of switch 1 of my server switches. trunk port with the VLANS of that switch.

When I do not create a L3 interface for this subnet i get the error "not in a configured subnet"

When i do create one it says "already routed" 

I have over 20VLANS so the 0.0.0.0/0 is very handy but I'm starting to think I have to create a route for every subnet and remove the 0.0.0.0/0 route to be able to define a different route for that subnet? 

Cheers,

Ben

[PhilipDAth]

You need a route for every subnet that points in a different direction to your default gateway - that is not also a directly connected interface (or layer 3 vlan).

[PhilipDAth]

You can't route 10.162.128.0/17 to 10.162.128.1 - they are both in the same subnet - that would be pointless.  Does the Alcatel have another layer 3 interface in a different VLAN that any of your other kit is also in?  You could add the 10.162.128.0/17 via that other interface.

If the Alcatel only has that one layer 3 interface then you don't need to route anything via it (you need at least two layer 3 interfaces to really do routing).  In that case you would simply add a layer 3 interface for that subnet onto one of your other devices, such as your core switches.

[Ben]

Ok, yeah makes sense. When i create a L3 interface it becomes a VLAN on the network.

I want to be able to tag those subnets on the SSID's with VLANS because people logging onto that specific SSID needs to be routed towards the Alcatel switch.

I just have to tag my VLANS on the correct ports to route them towards the alcatel.