In the last blog post in the VLANs and VRFs in netlab series, I described how we can combine VLANs and VRFs and create a VRF Lite solution with stretched VLANs. Wonder how hard would it be to create a routed multi-hop VRF Lite topology? It’s trivial.

Let’s start with the nodes. We won’t need any extra attributes on individual nodes, so we can define them as a simple list:

nodes: [r1, r2, r3, h1, h2, h3, h4 ]

Next, we’ll define two groups: Linux hosts and routers. We won’t define the device type in the routers group so you can use whatever devices you want as long as they support VLANs, VRFs and OSPF – the configuration modules we need to get the virtual interfaces and routing protocols up and running.

groups:
  routers:
    members: [ r1,r2,r3 ]
    module: [ vlan,vrf,ospf ]
  hosts:
    device: linux
    members: [ h1,h2,h3,h4 ]

Next, we need two VRFs and two VLANs (one per VRF). The magic trick that makes VRF Lite work is mode: route in VLAN definition that changes VLANs from a stretched bridging thingy to an interface encapsulation thingy – a different IP subnet is assigned to the VLAN instance on every physical link.

vrfs:
  red:
  blue:

vlans:
  red:
    mode: route
    vrf: red
  blue:
    mode: route
    vrf: blue

Speaking of links: here’s the list of links. The links between routers are VLAN trunks; the links between hosts and routers are simple Ethernet interfaces in VRFs:

links:
- r1:
  r2:
  vlan.trunk: [ red, blue ]
- r2:
  r3:
  vlan.trunk: [ red, blue ]  
- h1:
  r1:
    vrf: red
- h3:
  r1:
    vrf: blue
- h2:
  r3:
    vrf: red
- h4:
  r3:
    vrf: blue

That’s it. Execute netlab up -d your-device¹ (after downloading the final topology file) and you’ll have a multi-VRF lab using VLAN trunks.

Here are the relevant parts of Arista EOS configuration in case you’re wondering what we achieved with this simple lab topology file:

vlan 1000
   name red
!
vlan 1001
   name blue
!
vrf instance blue
   rd 65000:2
!
vrf instance red
   rd 65000:1
!
interface Ethernet1
   description r1 -> r2
   no switchport
!
interface Ethernet1.1
   description r1 -> [r2]
   encapsulation dot1q vlan 1001
   vrf blue
   ip address 172.16.6.1/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet1.2
   description r1 -> [r2]
   encapsulation dot1q vlan 1000
   vrf red
   ip address 172.16.7.1/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet2
   description r1 -> [h1] [stub]
   vrf red
   ip address 172.16.2.1/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet3
   description r1 -> [h3] [stub]
   vrf blue
   ip address 172.16.3.1/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Loopback0
   ip address 10.0.0.1/32
!
ip routing
ip routing vrf blue
ip routing vrf red
!
router ospf 100 vrf red
   router-id 10.0.0.1
   passive-interface Ethernet2
!
router ospf 101 vrf blue
   router-id 10.0.0.1
   passive-interface Ethernet3

Here’s the R2 configuration showing how multi-hop VRF lite works with VLAN subinterfaces:

vlan 1000
   name red
!
vlan 1001
   name blue
!
vrf instance blue
   rd 65000:2
!
vrf instance red
   rd 65000:1
!
interface Ethernet1
   description r2 -> r1
   no switchport
!
interface Ethernet1.1
   description r2 -> [r1]
   encapsulation dot1q vlan 1001
   vrf blue
   ip address 172.16.6.2/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet1.2
   description r2 -> [r1]
   encapsulation dot1q vlan 1000
   vrf red
   ip address 172.16.7.2/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet2
   description r2 -> r3
   no switchport
!
interface Ethernet2.1
   description r2 -> [r3]
   encapsulation dot1q vlan 1001
   vrf blue
   ip address 172.16.8.2/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet2.2
   description r2 -> [r3]
   encapsulation dot1q vlan 1000
   vrf red
   ip address 172.16.9.2/24
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Loopback0
   ip address 10.0.0.2/32
!
ip routing
ip routing vrf blue
ip routing vrf red
!
router ospf 100 vrf red
   router-id 10.0.0.2
!
router ospf 101 vrf blue
   router-id 10.0.0.2

Want to run this lab on your own, or try it out with different devices? No problem:

• Install netlab
• Download the relevant containers or create Vagrant boxes
• Download the topology file into an empty directory
• Execute netlab up -d your-device
• Enjoy! 😊