[nsp] Newbie OSPF Q.

[Gould, Aaron M (NRSW N61CR1W)]

oliver and group, if ospf discards the alternate paths and only enters the
least costly (most preferred) route into its rib, how does a ospf process
running in a router add a new (more costly/less preferred but good
nonetheless) route into its rib when the most preferred one goes down?
...i mean if it has no other routes to add to its rib because it previously
"discarded" them how will it accomodate an outage in the case of the more
preferred route dieing.

aaron

p.s.  i'm not sorry for asking a newbie question.  ha (just kidding)




Aaron Gould (CACI)
Network Engineer, PACSW/CNRSW/RITSC
619-545-2569
619-981-4900 cell
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-----Original Message-----
From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com]
Sent: Tuesday, April 20, 2004 2:08 AM
To: Fredrik.Jacobsson at enskilda.se
Cc: cisco-nsp at puck.nether.net
Subject: RE: [nsp] Newbie OSPF Q.


Hi,

> I'd like to see all possible paths to a network announced by OSPF.
> In my case I have three possible links, not having equal costs.
> 
> Is there a way to see all paths (as with sho ip route) where one can
> see paths with unequal costs. And the costs listed as well.

No, there is no way to see the alternate paths. You can take a look into
the LSA's and see which alternate node advertised the prefix, but this
doesn't give you what you're looking for. 
When we perform the SPF algorithm, only the best path(s) are entered
into the RIB, the alternate paths are discarded.

In IOS' ISIS implementation, there is a hidden knob
("display-route-detail") which shows you the backup paths (rather: the
LSP which contains it and the metric), but we don't do this for OSPF, as
far as I know.

	oli

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