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

From: "Kaliraj V - CTD, Chennai." <[email-masked]>
Date: Tue, 22 Jun 2004 14:23:16 +0530

>IMO, this would imply that a redistributed route enters directly into
>the Adj-Rib-Out of a peer potentially in preference to the best selected
>bgp route.

I feel for all practical-puposes a redistributed-route is Best-BGP route, so
it should be seen in the Loc-RIB too. 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.

> The routes that we receive from our peers are placed in the "Adj-Rib-In".
What about the
> routes that are redistributed (static/RIP/ISIS/OSPF/etc) in BGP?

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.  

Kaliraj.
-----Original Message-----
From: Jeffrey Haas [mailto:[email-masked]]
Sent: Monday, June 21, 2004 10:02 PM
To: John Smith
Cc: [email-masked]
Subject: Re: [Idr] Loc-Rib and Adj-Rib-In

On Fri, Jun 18, 2004 at 10:29:59AM +0100, John Smith wrote:
> Consider an instance where BGP is redistributing OSPF routes in it. BGP
runs its decision
> process and finds that these are the best routes and that it needs to
announce them to
> its peers. From a purist's language, will these routes now be placed in
the "Loc-Rib" ?
> 
> The routes that we receive from our peers are placed in the "Adj-Rib-In".
What about the
> routes that are redistributed (static/RIP/ISIS/OSPF/etc) in BGP?

It is intentionally hand-waved in the specification.  The closest
reference you will find to such a thing (from draft -23):

   All routes in the Loc-RIB are processed into Adj-RIBs-Out according
   to configured policy. This policy MAY exclude a route in the Loc-RIB
   from being installed in a particular Adj-RIB-Out. A route SHALL NOT
   be installed in the Adj-Rib-Out unless the destination and NEXT_HOP
   described by this route may be forwarded appropriately by the Routing
   Table. If a route in Loc-RIB is excluded from a particular Adj-RIB-
   Out the previously advertised route in that Adj-RIB-Out MUST be with-
   drawn from service by means of an UPDATE message (see 9.2).

IMO, this would imply that a redistributed route enters directly into
the Adj-Rib-Out of a peer potentially in preference to the best selected
bgp route.

>From the BGP MIB standpoint, just because a route is the best bgp route
doesn't mean we expect to see it in the adj-rib-out.

-- 
Jeff Haas 
NextHop Technologies

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From: Jeffrey Haas <[email-masked]>
Date: Tue, 22 Jun 2004 09:18:05 -0400

On Tue, Jun 22, 2004 at 02:23:16PM +0530, Kaliraj V - CTD, Chennai. wrote:
> 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,

>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.

> pseudo-RIB-In will override the best-bgp-route selected by the

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.

-- 
Jeff Haas 
NextHop Technologies