Problems with RD, RT import and RT export in MPLS VPN and BGP

Question

I'm learning MPLS VPN with MP-BGP and I'm finding difficulties with undertstanding the RD value and the RT import and export values.

From what I've already understand, RD (route distinguisher) identifies the VRFs from a network that compose the same virtual network and change routing info between them. RT import says what VRFs in a network are known by the local VRF and RT export is send to identify the information from the local VRF. To decide in what VRF install the rout, when a package comes to the PE, if the RT export the package has and the RT import our VRF have are the same, it adds the route to the VRF, otherwise it delete it.

I don't know if all I've written is correct. But I don't get to understand it properly when I find something like THIS.

Let's talk about sites PE1, PE2, PE3 and PEC (central PE).

What sites does PE3 know?

As the RT import is the RT export of PEC, PE3 just knows PEC.

What sites does PEC know?

I think PEC knows PE1 a PE2 because RT export from PE1 and PE2 matchs with RT import from PEC.

Am I correct? Please I need help to understand it.

score 1 · Accepted Answer · answered Jun 16 '19 at 18:25

From what I've already understand, RD (route distinguisher) identifies the VRFs from a network that compose the same virtual network and change routing info between them.

That’s not right. RD is added to the IP address to make them unique. It does not define virtual networks.

RT import says what VRFs in a network are known by the local VRF and RT export is send to identify the information from the local VRF.

Nope. Think of route targets as a “tag” that identifies routes. Export tags the routes and Import selects which tags are imported into the VRF.

To decide in what VRF install the route, when a package comes to the PE, if the RT export the package has and the RT import our VRF have are the same, it adds the route to the VRF, otherwise it delete it.

Also not right. MP BGP carries all the routes. Import/export is used to select which ones are included in a VRF.

Thank you very much for the answer. It helped me. Can you tell me if I'm wrong too in my exercise? — wasanga7, Jun 17 '19 at 15:14
Your answers are wrong. Look at the information I provided and see how you would change your answers. — Ron Trunk, Jun 17 '19 at 15:41

Problems with RD, RT import and RT export in MPLS VPN and BGP

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