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I know the explanation about the usage of RD, that it makes routes from different VRFs globally unique. AFAIK, a VPN route is composed of [RD] + [VPN label] + [Prefix] Isn't the VPN label, that is allocated for each VRF anyway, enough to make the route globally unique? Isn't [VPN label] + [prefix] unique enough?

Is RD used because it's user configurable and allows for more control? unlike VPN labels that are randomly allocated by the router.

Or maybe RD is used - since a VPN label isn't always mapped directly to a VRF (maybe sometimes it's mapped to a route directly, to save a VRF IP lookup when forwarding traffic towards a CE router)

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AFAIK, a VPN route is composed of [RD] + [VPN label] + [Prefix]

That's not correct. A route is RD + prefix.

Remember packets have labels -- routes have distinguishers

An MPLS VPN is a bit abstract. It's a collection of VRFs that share a common route policy.

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  • so is it possible that two or more VRFs are represented by a single a label? (Should they have the same RD in that case?) – manish ma Jun 11 at 7:18
  • You are confusing two separate things. Labels do not define VPNs – Ron Trunk Jun 11 at 12:14
  • So what do VPN labels define then? – manish ma Jun 11 at 13:34
  • They define the flow from the ingress LSR to the egress LSR. – Ron Trunk Jun 11 at 14:07
  • There are two labels, I'm talking about the inner label that represents the VRF – manish ma Jun 11 at 16:54

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