Subject: RE: [Idr] Loc-Rib and Adj-Rib-In

From: "Kaliraj V - CTD, Chennai." <[email-masked]>
Date: Tue, 22 Jun 2004 21:40:55 +0530

Jeff, from your expln I understand LocRIB is viewed as comprising of only
BGP-learnt routes.

>From the MIB view point, the best route is the one in the Loc-Rib.

But this should be really confusing. Assuming a BGP speaker has, for a
prefix P: a BGP-best route R1(LocRIB) and a redistributed non-BGP route
R2(result-of-Policy); R2 by policy overrides R1. So the speaker is using R2
and not R1 as reachablity-information for P. Now, if the MIB shows as
best-route the route in the Loc-RIB i.e. R1, then this seems misleading to
me as the speaker is not using this route. 

I suggest either R2 be considered part of Loc-RIB or the MIB view-point be
altered so that it is not confined to Loc-RIB.

Thanks,
Kaliraj.
-----Original Message-----
From: Jeffrey Haas [mailto:[email-masked]]
Sent: Tuesday, June 22, 2004 6:48 PM
To: Kaliraj V - CTD, Chennai.
Cc: [email-masked]
Subject: Re: [Idr] Loc-Rib and Adj-Rib-In

On Tue, Jun 22, 2004 at 02:23:16PM +0530, Kaliraj V - CTD, Chennai. wrote:
> I feel for all practical-puposes a redistributed-route is Best-BGP route,
so
> it should be seen in the Loc-RIB too.

There are two issues with this, IMO:

1. A route that is redistributed into BGP, potentially in preference to
   a route that is the "best BGP route", is not a BGP route until it
   is sent to the neighboring BGP peer.  The local system will simply
   treat it as a route from whatever protocol (OSPF, IS-IS, etc.) it came
   from.
2. While the clarity of getting non-BGP information injected into BGP
   is a little vague, the processing of BGP routes into the Loc-Rib
   is quite clear:

   [draft -24, 9.1.2]
   : The local speaker SHALL then install that route in the Loc-RIB,
   : replacing any route to the same destination that is currently being
   : held in the Loc-RIB. 

   See also draft -24 3.2.2.b

> For eg. from the BGP MIB view-point,
> we'd like to see the redistributed-BGP route as the Best-BGP route for the
> corresponding prefix, even if it has not been advertised to any peers i.e.
> not present in Adj-RIB-Out of any peer. Please correct me if wrong.

>From the MIB view point, the best route is the one in the Loc-Rib.
This probably should have been clarified in the v1 MIB but it can
go into the v2 MIB.  I don't think we need to backout of last call
on the MIB for this clarification.

> May be we can imagine a pseudo-RIB-In for these routes, which will not
take
> part in the BGP-path-selection-process but any competitor available in
this
> pseudo-RIB-In will override the best-bgp-route selected by the
> selection-process.  

The general problem is that the RIB model is reasonably well suited
for BGP-only information with some vagaries as to how information from
other protocols is redistributed into BGP.  To clarify this, we would
need to discuss the details of the Policy Information Base and 
the Routing Table and that would take us into implementation details
we really don't want to have done by IDR.

The problem with your suggestion of "any competitor available [...] will
overide" is that this is a matter of policy, which is dealt with in the
section from my original paste.

> Kaliraj.

-- 
Jeff Haas 
NextHop Technologies

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---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 22 Jun 2004 19:27:16 -0400

> me as the speaker is not using this route. 

This would only be misleading if the MIB stated in its Adj-Rib-Out that
it was using a given BGP route.

Note that the v2 MIB has added an Adj-Rib-Out table.  The contents
of this table was contentious when it was added and we have not
received consensus as to the contents.

> altered so that it is not confined to Loc-RIB.

Loc-Rib will contain the BGP Best route.  The MIB must reflect this
since this is what the BGP specification indicates.  This route is
then installed in the Routing Table.

It is at this point that implementation specific magic happens.

As a for example, you could consider your Routing Table as having
the ability to learn multiple routes from each protocol that is
going to install routes there.  Through an internal policy mechanism,
the multiple candidate routes will become the Routing Table's active
route and that route will presumably be installed in the FIB.

This active Routing Table route, when not the same as the Loc-Rib
route, is available to BGP for redistribution (and technically
origination).

The details of how this works and model by which the Routing Table
is modeled, is outside the scope of the IDR working group.  To do
more than to reflect what was sent in BGP via the Adj-Rib-Out
table as a BGP route is probably out of scope.  However, I've recently
become aware of a MIB TC that may let us reflect what protocol the route
came from.  This will like show up in the next draft of the MIB.

It really seems that what you want is a Routing Table MIB.

-- 
Jeff Haas 
NextHop Technologies