The MPLS-OPS Archive

["Mark Lewis" <markl11@hotmail.com>]

Hi,

On a PE router, there is one VRF per connectivity requirement.
To illustrate this, suppose the PE router in question is connected to the 
following:

1. A site in VPN A (which only requires intra-VPN connectivity)
2. Two sites in VPN B (both requiring only intra-VPN connectivity)
3. A site which requires connectivity to both VPN A and VPN B

In the above example there are a total of four sites, but only three 
connectivity requrements, and therefore you would have THREE VRFs.

As to route lookup within a VRF, it is the same as would be true for a 
regular routing table - based on longest match.
Import of routes into VRFs is very important here. Routes are imported into 
VRFs based upon Route Targets (RT).
Routes are exported from VRFs with certain RTs (RTs are BGP extended 
communities, and take the form <type><AS number><32bitvalue>, or <type><IP 
address><16bitvalue>).
To provide communication to other sites, you simply import routes with the 
appropraite RTs to the site VRF.
This methodology allows the provisioning of very complex topologies 
(connectivity models), eg. simple VPNs, overlapping VPNs, hub-and-spoke 
VPNs, etc.

Hope that helps,

Mark Lewis
Frontrunner Solutions


>From: "Bala Subrahmanyam Venkata" <bsubrahm@doradosoftware.com>
>To: <mpls-ops@mplsrc.com>
>Subject: VRF table lookup for Sites with mutiple VPN membership...
>Date: Thu, 26 Apr 2001 13:55:51 -0700
>
>I have a basic doubt about how the VRF lookup is made in the case of a
>BGP/MPLS VPN. Suppose if in my MPLS VPN I have a Site that is connected to
>(an interface in ) a PE Router and is a member of more than one VPN. Which
>of these assumptions is valid:
>
>1. There will be one VRF table for that Site in the PE
>2. There will be one VRF table per VPN of which the Site is a member
>
>If 1. is true then how is the lookup performed for a packet that is 
>destined
>for one particular VPN from the Site ? Is this true even if there are
>multiple Sites connected to the same PE Router ?
>
>I remember coming across a doc that had a pictoral description of a VRF
>table...does anyone have it ?
>
>
>TIA
>
>bala
>
>
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