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MPLS : Route Distinguisher (RD) vs Route Target (RT)

March 07, 2024 , ,

MPLS : Route Distinguisher (RD) vs Route Target (RT)

Route Distinguishers (RDs) and Route Targets (RTs) are two critical elements in MPLS Layer 3 VPNs. Understanding the difference between RDs and RTs is critical for properly building and operating MPLS L3 VPNs. They collaborate to ensure effective routing and segmentation of consumer traffic across the service provider's network.

⭐Related : MPLS ( RD and VRF concept )
⭐Related : Introduction to MPLS Route Target (RT)

Route Distinguisher (RD) vs Route Target (RT)
Fig 1.1- RD vs RT

 Route Distinguisher (RD)

A Route Distinguisher (RD) distinguishes between routes (one VRF for each customer routing table) for one customer and others. To identify which VPN a route belongs to, RD (a 64-bit identification) is prepended to it within a VRF. 

When sharing VPN routes with other PE routers, an RD is sent along with the route using MP-BGP. In short, RD is used to distinguished the same subnet getting from two different customer

Route Distinguisher (RD) Format

⭐Related : MPLS ( RD and VRF concept )

 Route Target (RT)

Route Target (RT) is a 64-bit identifier that is used as part of the MP-BGP attribute (extended community) to determine which routes should be exported or imported into a certain VPN. Route distinguishers are used to ensure that similar routes in various VRFs remain distinct, although route targets can be used to share routes between them. We can use route targets in a VRF to regulate route import and export.

RT ( Route Target ) comes into the pictures when you have multiple remote sites which is connected to MPLS. So there are two concepts of Import and export in RT, so now the question is where these import and export are being used.

On any VRF, when you configure RT import, it imports all the prefixes that matches the configured RT value as one of the attribute in the BGP update. So in any-any VRF, it is common to see all PE configured with same RT value (You may see more RT depending on inter-VRF scenarios).

So RT is used to export the routes from one site and import at other side and vice versa. So by using import and export you can have the specific routes at the sites. It's the concept of the route filtering for specified site.

⭐Related : Introduction to MPLS Route Target (RT)

 Route Distinguisher (RD) Vs. Route Target (RT)

Let's talk about the difference between Route Distinguisher (RD) and Route Target (RT) as both are used in the MPLS network 

Route Distinguisher (RD) Vs. Route Target (RT)

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