[c-nsp] general question on VRFs and FIBs...

[Vitkovsky, Adam]

Hi,
So is junos and ios really coded to carve up a separate FIB tables each 
with it's own table preamble and stuff + adjacency table for each vrf? 

As I believe it's possible to have a common FIB with some sort of a marker asociated with each table entry -describing the vrf participation
Than wen you come out an interface asociated with a particular marker (vrf)
the lookup would be done only on a subset of prefixes with the marker matching the one asociated with the interface 
-though I'm not sure whether this would work with the common adjacency table and it's l2 overrides

Now in dcef mode
With a separate FIB+Adjacency tables per vrf
You could copy only subset of FIB and Adjacency tables to the linecard based on which vrfs the interfaces on the particular line-card are asociated with
-to save up some memory
(than a proces would be needed to request FIB resend from the RP when interface on a line-card would be asociated with a new vrf) 


adam
-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Gert Doering
Sent: Tuesday, September 27, 2011 9:58 AM
To: Derick Winkworth
Cc: juniper-nsp at puck.nether.net; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] general question on VRFs and FIBs...

Hi,

On Mon, Sep 26, 2011 at 01:18:05PM -0700, Derick Winkworth wrote:
> I'm trying to find an archived discussion or presentation discussing
> why exactly the industry generally settled on having a separate
> FIB table for each VRF vs having one FIB table with a column that
> identifies the VRF instance?  I'm not finding it, but I'm guessing
> its because of performance issues?    

Lookup would fail for overlapping address space if you lookup 
"address first, VRF second".

How do you find the right entry if you have

  10.0.0.0/8 vrf red
  10.0.0.0/16 vrf green
  10.0.1.0/24 vrf blue

and try to look up 10.0.0.1 in vrf red?  You'll find the /24 entry, which
is tagged "vrf blue".

Alternatively, you'd need to explode the /8 entry for vrf red if *another*
VRF adds a more specific for that /8.

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de