[nsp] CEF routing bug?

[Todd, Douglas M.]

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Ilker:

Really, I thought the adacency was created when there is an IGP route
in the routing table and the NHR is available.
Is that not where the cached adjacency comes from when we do a sh ip
cef detail.
Could you clarify?

==DMT>

> -----Original Message-----
> From: Ilker Temir [mailto:itemir at cisco.com]
> Sent: Thursday, January 30, 2003 11:24 AM
> To: Roy
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [nsp] CEF routing bug?
> 
> 
> > It looks like CEF creates the /32 adjacency based on the 
> ARP irrespective
> of
> > whether or not its the correct route.
> 
> Wrong interpretation, CEF creates a /32 adjacency only if the entry
> is directly connected. Adjacency is created when there is no IGP 
> route in the
> routing table.
> 
> Ilker
> 
> > The basic bug is that the route used is different based on 
> whether or not
> CEF is
> > on and that seems to be a bug.
> >
> > Ilker Temir wrote:
> >
> > > If you lose the route from your IGP, the network will be
> > > directly 
> connected.
> > > And CEF will create /32 adjacency based on ARP, as long 
> as this spesific
> > > adjacency exists it will be used even if the route is 
> relearned from IGP
> > > (since adjacency created from IGP will be less spesific).
> > >
> > > If arp times out, corresponding /32 CEF adjacency will be 
> removed and
> there
> > > will be no problem. However arp will never time out in 
> this case (unless
> > > remote goes down). And to me, it is logical. Why would you want
> > > to 
> remove an
> > > arp entry when the directly connected destination is 
> still reachable ?
> > >
> > > Better change your design.
> > >
> > > Ilker
> > >
> > > ----- Original Message -----
> > > From: "Ed Ravin" <eravin at panix.com>
> > > To: <cisco-nsp at puck.nether.net>
> > > Sent: Thursday, January 30, 2003 12:33 AM
> > > Subject: [nsp] CEF routing bug?
> > >
> > > > Roy writes:
> > > > > I have two routers ("A" and "B") and both are 
> directly connected to
> LAN
> > > > > "C" ( a /26 subnet) [...]
> > > > > For various reasons, I prefer the traffic on router 
> "A" to go to LAN
> "C"
> > > > > via router "B".  I do this my entering more specific 
> routes for LAN
> "C"
> > > > > pointing to router "B" (two route of /27).  This 
> works fine until I
> turn
> > > > > on CEF.  When I do that, the direct connection is always
> > > > > used 
> instead of
> > > > > the indirect routes.
> > > >
> > > > I'm seeing similiar problems on two different routers - 
> a 7206 with
> > > > 12.2(7c) and a 7513 with 12.0(21)S1.  On one router, 
> routes received
> > > > via OSPF or RIP do not override CEF when the CEF route is on
> > > > a FastEthernet interface.  On the other router, the 
> dynamic routes are
> > > > used when the router is restarted, but if the dynamic routing
> > > > protocol drops the route and CEF takes over, we can't 
> lose the CEF
> > > > route without rebooting the router again.
> > > >
> > > > _______________________________________________
> > > >
> >
> 
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