Inter-VRF Routing with VRF Lite

[iores]

Hi,

I am referring to the topology from this article: https://packetlife.net/blog/2010/mar/29/inter-vrf-routing-vrf-lite/

How is Layer 3 connection established between the multi layer switches when they don't have any physical interface with configured IP address? They only have VLAN interfaces. In addition, the link between SW1 - SW2 and SW1 - SW3 is configured as trunk.

What am I missing out here? 

P.S. The configuration files for all three switches can be found at the end of the article.

[balaji.bandi]

As per the design, they do have a Layer 3 interface and part of VRF.

or you question if you like to deploy Layer 2 switch between?

[iores]

SW2 and SW3 have VLAN interfaces which act as a default gateway for VLANs 216 & 217 (Building 2), and 316 & 318 (Building 3).

In order to create inter-building connectivity, there needs to be Layer 3 connectivity between switches. I assume that was achieved with VLAN interfaces 16, 17, and 18.

So routing and IGP adjacency can be established between VLAN interfaces even though the physical interface is configured as Layer 2? I thought this should be the same as with loopback interfaces & routers and the fact that adjacency cannot be established between them.

In addition, inter-building connectivity could easily be achieved by using only VLAN interfaces that act as a default gateway, right? So why those additional VLAN interfaces (16, 17, 18) on switches 2 and 3? Isn't enough for SW 1 to have only one red, green, and blue VLAN interface? Is it because it is much easier to achieve OSPF adjacency with lessen VLAN interfaces on SW3 because otherwise we would need, for example, two red VLAN interfaces - one for each red subnet on SW2 and SW3?

[MHM Cisco World]

each L3SW is with VRF now three L3SW 
this called virtual, 
 
so L3SW1 virtual RED is VRF RED OSPF adjust with L3SW2 virtual RED
so L3SW1 virtual RED is VRF RED OSPF adjust with L3SW3 virtual RED
so L3SW2 virtual RED is VRF RED OSPF adjust with L3SW3 virtual RED

so L3SW1 virtual BLUE is VRF BLUE OSPF adjust with L3SW3 virtual BLUE

so L3SW1 virtual GREEEN is VRF GREEN OSPF adjust with L3SW3 virtual GREEN

How is Layer 3 connection established between the multi layer switches when they don't have any physical interface with configured IP address? trunk all VLAN, each L3SW virtual use it SVI to adjust with other L3SW virtual. 

[Joseph W. Doherty]

"How is Layer 3 connection established between the multi layer switches when they don't have any physical interface with configured IP address?"

You've (correctly) answered your own question with "They . . . have VLAN interfaces."

"In addition, the link between SW1 - SW2 and SW1 - SW3 is configured as trunk."

"What am I missing out here?"

Yes they are.  Unsure what you're missing, unless injecting VRFs is confusing you.

Are you familiar with having two switches L3 intercommunicate other than using routed ports?

I.e. do you understand how to support the following: R1 192.168.1.1/24 <> SW1 <> SW2 <> 192.168.1.2/24 R2 - on a pair of L3 switches without using routed ports?

[iores]

@Joseph W. Doherty 

The R1 and R2 will be able to communicate to each other if they are in the same subnet/vlan and the link between switches is configured as trunk.

Is this what you had in mind?

[Joseph W. Doherty]

"Is this what you had in mind?"

Not exactly.

What I had in mind was two routers connected through two L2 non-VLAN capable switches.

R1 and R2 would be able to intercommunicate between their interfaces, both routers' interfaces being in the same network.

You could, though, do the same with two VLAN capable switches.  Trunk need not be used, but three physical links connecting the two routers and two switches must be the same VLAN (to provide a L2 path, like the non-VLAN capable switches, for the routed connection).

If you understand the forgoing, you can do the above with two L3 switches, where they interconnect on a shared VLAN (usually across a trunk, but could be access ports link) and the routers interfaces are replaced by SVIs.

[MHM Cisco World]

friend 
do show ip route 
or in your case 
show ip route vrf <x>
do you see the IP ? if yes then the OSPF can use it 

the IP appear in routing table if L1 L2 is UP/UP and the interface have IP