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

From: "Kaliraj V - CTD, Chennai." <[email-masked]>
Date: Wed, 23 Jun 2004 13:01:21 +0530

>This would only be misleading if the MIB stated in its Adj-Rib-Out that it
was using a given BGP route.
I agree. I guess this is clear. LocRIB is the protocol's view of the
best-route. Adj-RIB-out gives the results of policy too(redistribution
but-not outbound-routemaps asper MIBv2).

SO, in MIBv2 terms: a redistributed route will get into Adj-RIB-In
(NLRItable) and will override the LocRIB(bestroute asper LocRIB) to directly
enter Adj-RIB-Out (be pointed to by the Rowpointer-object
bgpM2AdjRibsOutRoute) for that NLRI prefix.

>However, I've recently become aware of a MIB TC that may let us reflect
what protocol the route came from.  
This feels like Good to have information, though not really needed for BGP
to know-about.

>It really seems that what you want is a Routing Table MIB.
Not really, I'm happy with presence of Adj-RIB-Out to tell me what BGP
actually used.:)

Thanks,
Kaliraj.
-----Original Message-----
From: Jeffrey Haas [mailto:[email-masked]]
Sent: Wednesday, June 23, 2004 4:57 AM
To: Kaliraj V - CTD, Chennai.
Cc: [email-masked]
Subject: Re: [Idr] Loc-Rib and Adj-Rib-In

On Tue, Jun 22, 2004 at 09:40:55PM +0530, Kaliraj V - CTD, Chennai. wrote:
> 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. 

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.

> 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.

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.

> Kaliraj.

-- 
Jeff Haas 
NextHop Technologies

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