The MPLS WG Archive

[Ben Black <ben@layer8.net>]

Perhaps James is drawing attention to the ambiguity of the first
section stating that VRFs are per _site_, but the second section
stating that VRFs are per _interface_ (allowing for multiple
connections from the same site to be treated independently).


ben

On Wed, Dec 13, 2000 at 04:48:28PM -0800, Andrew Wu wrote:
> Here is my quick take on this:
> 
> Typically, one (sub)interface on a PE is connected 
> to one CE device and that the (sub)interface at same 
> time is associated with one VRF on the PE. So the 
> packets coming from the (sub)interface will 
> be forwarded upon the result of the lookup in that 
> VRF(the (sub)interface is associated with ).
> 
> On a PE:
> ===========================
> (sub)interface1----> VRF1
> 
> 
> (sub)interface2 ----> VRF2
>            
>                        ^
>                        |
>                        |
>                    (sub)interface2
> 
> 
> -andrew
> 
> -----Original Message-----
> From: James_Huang@Mitel.COM [mailto:James_Huang@Mitel.COM]
> Sent: Wednesday, December 13, 2000 4:22 PM
> To: mpls@UU.NET
> Subject: How to map a packet to a VRF for route lookup?
> 
> 
> Hi all,
>      I am very confused by the description in RFC2547bis with regarding to
> the
> association of VRFs and CE sites.  In section 1.3 of RFC2547bis, the
> following
> description is given:
>      "Each PE router maintains a number of separate forwarding tables.
>      Every site to which the PE is attached must be mapped to one of those
>      forwarding tables."
> 
>      Also in section 3, the following text is given:
>      Each PE router maintains one or more "per-site forwarding tables."
>      These are known as VRFs, or "VPN Routing and Forwarding" tables.
>      Every site to which the PE router is attached is associated with one
>      of these tables.  A particular packet's IP destination address is
>      looked up in a particular VRF only if that packet has arrived
>      directly from a site which is associated with that table.
> 
>      From these descriptions,  one would conclude that a CE site is
> associated
> with exactly one VRF.  But the description in another paragraph of section
> 1.3
> seems to indicate otherwise:
>      A PE router is attached to a site by virtue of being the endpoint of
>      an interface or "sub-interface" (PVC, VLAN, GRE tunnel, etc.) whose
>      other endpoint is a CE device.  If there are multiple attachments
>      between a site and a PE router, all the attachments may be mapped to
>      the same forwarding table, or different attachments may be mapped to
>      different forwarding tables.  When a PE router receives a packet from
>      a CE device, it knows the interface or sub-interface over which the
>      packet arrived, and this determines the forwarding table used for
>      processing that packet.  The choice of forwarding table is NOT
>      determined by the user content of the packet.
> 
>      The above description seems to associate an interface or subinterface
> with
> a VRF.
>      Am I missing somethin here?
> 
> 
> -- James Huang
> 

-- 
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