Cisco IOS - How to Configure VRF-Lite

What is VRF-Lite?

VRF is a feature that allows you to create separate instances of the routing table. In turn allowing you to segregate and isolate different network types. When VRFs are used without MPLS it is classed as VRF-lite. VRF-lite configuration doesn’t need the route-target and can be done by static or dynamic routing under its VRF instance.^[1]

Topology

This tutorial will be based on the following topology (Figure 1):

• 2 x VRFs will be configured on router R1 - Green/Red.
• 2 x networks (100.1.1.0 and 200.1.1.0) will be configured on router R1, one placed into each of the VRFs.
• eBGP peerings will then be established to each of the neighbours (Red/Green).
• eBGP will advertise the corresponding VRF network to its peer:
  • Green VRF - 100.1.1.0.
  • Red VRF - 200.1.1.0.

Figure 1 - Topology.

Configuration

Router - R1

VRFs

First of all we configure the 2 VRFs. Each VRF is assigned a Route Distinguisher.

ip vrf GREEN
  rd 65001:100
  
ip vrf RED
  rd 65001:200

Interfaces

Next, we configure our interfaces. Each loopback and the interface connecting R1 to its neighbor is placed into their corresponding VRF.

interface Loopback1
  ip vrf forwarding GREEN
  ip address 100.1.1.1 255.255.255.0
!
interface Loopback2
  ip vrf forwarding RED
  ip address 200.1.1.1 255.255.255.0

interface GigabitEthernet0/1
  description to GREEN
  ip vrf forwarding GREEN
  ip address 10.0.0.10 255.255.255.252
!
interface GigabitEthernet0/2
  description to RED
  Ip vrf forwarding RED
  ip address 10.0.0.5 255.255.255.252

BGP

BGP is configured. We use the IPv4 address families to specify our VRFs and redistribute our connected interfaces into BGP.

Note : The IPv4 address-family exchanges normal IPv4 unicast routes, without any route distinguisher (RD). Therefore in our example the RD is only locally significant to R1, hence vpnv4 being used within the R1 show commands.

router bgp 65001
  bgp router-id 1.1.1.1
  bgp log-neighbor-changes

  address-family ipv4 vrf GREEN
    redistribute connected
    neighbor 10.0.0.9 remote-as 65002
    neighbor 10.0.0.9 activate
  exit-address-family

  address-family ipv4 vrf RED
    redistribute connected
    neighbor 10.0.0.6 remote-as 65003
    neighbor 10.0.0.6 activate
  exit-address-family

Router - Green

The configuration for Green, is a simple eBGP peering. Like so,

router bgp 65002
  bgp router-id 2.2.2.2
  bgp log-neighbor-changes
  redistribute connected
  neighbor 10.0.0.10 remote-as 65001

Router - Red

We then configure another eBGP peering on Red.

router bgp 65003
  bgp router-id 3.3.3.3
  bgp log-neighbor-changes
  redistribute connected
  neighbor 10.0.0.5 remote-as 65001

Verification

BGP Adjacencies

First, we will check that the BGP adjacencies have correctly formed on R1, Green and Red. From the output, we can see BGP has successfully established adjacency with its neighbour, and that prefixes have been received.

R1#show ip bgp vpnv4 vrf RED summary 
!
Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.0.0.6        4        65003      36      36        8    0    0 00:28:46        2

R1#show ip bgp vpnv4 vrf GREEN summary 
!
Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.0.0.9        4        65002      51      51        8    0    0 00:42:07        2

GREEN#show ip bgp summary
!
Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

10.0.0.10       4        65001      58      59        7    0    0 00:49:01        2

RED#show ip bgp sum
!
Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.0.0.5        4        65001      46      46        5    0    0 00:38:11        2

Routes

Finally, we check the routing table on, both the Green and the Red router, in order to confirm we have learnt the routes advertised from the corresponding VRF on R1.

GREEN#show ip route  
!
      2.0.0.0/32 is subnetted, 1 subnets
C        2.2.2.2 is directly connected, Loopback0
      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        10.0.0.8/30 is directly connected, GigabitEthernet0/1
L        10.0.0.9/32 is directly connected, GigabitEthernet0/1
      100.0.0.0/24 is subnetted, 1 subnets
B        100.1.1.0 [20/0] via 10.0.0.10, 00:49:06

RED#show ip route
!
      3.0.0.0/32 is subnetted, 1 subnets
C        3.3.3.3 is directly connected, Loopback0
      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        10.0.0.4/30 is directly connected, GigabitEthernet0/1
L        10.0.0.6/32 is directly connected, GigabitEthernet0/1
B     200.1.1.0/24 [20/0] via 10.0.0.5, 00:38:05

Success, as we can see the advertised router from R1’s VRF on each router.

References