VRF-lite

Virtual Routing and Forwarding - lite

General information on “VRF-lite”:

VRF-lite = VRF without MPLS
VRF creates virtual router instances within a router
Each VRF instance maintains its own routing table
By default, VRF instances don’t know about each others routing table
VRF instances are mapped to interfaces
If the VRF instance is mapped after the interface' IP is configured, it will drop the IP configuration
Two or more interfaces can have the same IP address and subnet if they’re in different VRFs

VRF feature route-replicate:

With route-replicate it’s possible to “copy” the routes from one VRF routing table to another VRF routing table

VRF feature “Route Distinguisher (RD)":

MP-BGP feature
When several VRFs use the same subnet there needs to be a way to keep track of which routes belong to which VRF
RDs add a 8-byte identifier to each route to distinguish them from each other Can only be set globally for the VRF
RDs don’t need to be configured by default but have to when route-sharing is used
Types of RDs:
- Type 0: 2-byte ASN + 4-byte value (used for VPNv4 prefixes)
- Type 1: 4-byte IP + 2-byte value (used for VPNv4 prefixes)
- Type 2: 4-byte ASN + 2-byte value (used to signal multicast VPN)
RD + IPv4/v6 prefix = VPNv4/v6 prefix
Example (Type 0): RD is 65432:100, IPv4 prefix is 10.0.0.0/24 = VPNv4 prefix will be 0:65432:100:10.0.0.0
Example (Type 1): RD is 172.16.1.1:100, IPv4 prefix is 10.0.0.0/24 = VPNv4 prefix will be 1:172.16.1.1:100:10.0.0.0
Example (Type 2): RD is 65432:100, IPv4 prefix is 10.0.0.0/24 = VPNv4 prefix will be 2:65432:100:10.0.0.0

VRF feature “Route Targets (RT)":

MP-BGP feature
A RT is simply an extended community value for a route
Used to share routes between different VRFs
RT is a 8-byte field
The export keyword defines the value which an VRF exports its own routes to
The import keyword defines the value which an VRF imports routes from
Thumb rule is to use the same RD/RT for a given VRF (doesn’t have to be but makes it less confusing)
Can be set differently for the IPv4 and IPv6 address-family
Important: Export RTs are attached as BGP extended community to prefixes received from CE routers!

VRF feature “Import/Export map”:

MP-BGP feature
Route leaking/sharing between VRFs is normally done using Route Targets
But this method is not suitable between when routes from/to the global VRF need to be imported/exported
To accomplish route leaking/sharing from/to the global VRF, import/export maps must be used
Important: The prefix must be in the BGP table to be able to be imported/exported!

Configuration steps of “VRF-lite”:

Create VRF instance
Map interface to VRF instance
Configure the interface (IP address, …)
Map routing protocol instance to VRF instance
Configure the routing protocol instance

“VRF(-Lite)” CLI configuration commands:

## Configuring a VRF
Router(config)# vrf definition <vrf-name>
Router(config-vrf)# address-family [ipv4 | ipv6]

## Assigning an interface to a VRF
Router(config)# interface <if>
Router(config-if)# vrf forwarding <vrf-name>

## Replicating routes within a VRF
Router(config)# vrf definition <vrf-name>
Router(config-vrf)# address-family [ipv4 | ipv6]
Router(config-vrf-af)# route-replicate from vrf [global | WORD] [unicast | multicast] [protocol] route-map [ROUTE-MAP-NAME]

## Configuring a Route Distinguisher (RD)
Router(config)# vrf definition <vrf-name>
Router(config-vrf)# rd <rd-value>

## Configuring a Route Target (RT) 
Router(config)# vrf definition <vrf-name>
Router(config-vrf)# route-target [export | import] <rt-value>

## Configuring route leaking between GRT and VRF using import/export maps
Router(config)# vrf definition <vrf-name>
Router(config-vrf)# address-family [ipv4 | ipv6]
Router(config-vrf-af)# [import | export] [ipv4 | ipv6] unicast map [ROUTE-MAP-NAME]

“VRF(-Lite)” CLI show commands:

## Showing a brief overview of all VRFs
Router# show vrf

## Showing a brief overview of a specific VRF
Router# show vrf <vrf-name>

## Showing detailed information of all VRFs
Router# show vrf detail

## Showing detailed information for a specific VRFs
Router# show vrf detail <vrf-name>

## Showing interfaces and their VRF belonging
Router# show vrf [ipv4 | ipv6] interfaces

## Showing the routing table for a specific VRF
Router# show [ip | ipv6] route vrf <vrf-name>