We already discuss what is
MPLS and
LDP in the previous
sections. In this section, we will see what is
MPLS L3 VPN? And what are VRF
(virtual routing forwarding), Rd (route-distinguisher), RT (route-target), and
how to configure
MPLS L3 VPN in the service provider network?
In
MPLS Layer 3 the service provider will participate in
routing with the customers. The customers will run static, OSPF, EIGRP, BGP, or
any other routing protocol with the service provider; these routes can be
shared with other sites of the customers.
In VPN routing information from one customer is completely
separated from other customers and tunneled over the service provider MPLS
network.
What is VRF (virtual routing forwarding)?
Virtual routing forwarding VRF provides a way for us to
configure multiple routing instances on our router.
We use multiple routing tables. Each customer of the service
provider will use a different VRF.
VRF keeps customer traffic and routing separate utilizes the same hardware. Without VRF we need to use ACL filtering to
keep traffic segregated.
What is Rd (route-distinguisher?)
Route-distinguisher is used to convert a client non-unique
32-bit address into a unique 96-bit vpnv4 address, to enable transport between
PE routers and the resulting address is a vpnv4 address. RD is locally
significant to a router. VRF is not operational unless you configure an RD.
We can use any value we want but we use the ASN: NN format
where ASN means the service provider’s AS number and NN is a number we
pick that identifies the site of the customer. Each VRF in a PE router must
have a unique RD.
RT (Route-Target)
Is a 64-bit extended BGP community that is attached to aVPNv4 BGP route to indicate its VPN membership?
Any number of RTs can be attached to a single route.
Export RTs
1.
Identifies the VPN member to which the
associated VRF belongs.
2.
2. Are attached to a client’s route, when it is
converted into a VPNv4 route.
Import RTs
1. Import RT is used to select
which VPNv4 routers is to be inserted into which VRF tables.
2. on the receiving PE router, a
route is imported into a VRF only if at least one RT attached to the route
matches at least one import RT configuration in that VRF.