Subject: RE: How to map a packet to a VRF for route lookup?

From: Andrew Wu <[email-masked]>
Date: Wed, 13 Dec 2000 16:48:28 -0800

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: [email-masked] [mailto:[email-masked]]
Sent: Wednesday, December 13, 2000 4:22 PM
To: [email-masked]
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

---

From: Ben Black <[email-masked]>
Date: Wed, 13 Dec 2000 16:52:46 -0800

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

-- 
what great thing would you attempt if you knew you could not fail?