From: Chuck Larrieu (chuck@xxxxxxxxxxxxx)
Date: Sun Dec 24 2000 - 15:12:24 GMT-3
Just got through with one of the multiprotocol redistribution practice labs
( Mentor Labs 4141 )
Got a question regarding virtual links and loopback RIDs.
In the realm of OSPF, when direct ( meaning through the OSPF process )
access to a particular router is lost, does that mean that any virtual link
associated with that router is lost? Well, yes, I know, and duh!
But my question has to do with the placement of the RID into the routing
process.
The deal is that there is an alternative link to the OSPF area 0. However it
is through a different routing protocol. All routes are redistributed
through that protocol, and when the direct i.e. OSPF link between the two
endpoints of the virtual link are severed, even though the route to the RID
is seen via the redistribution process, the virtual link apparently does not
come back up.
This leads back to the question of the value of loopback addresses as a cure
all for routing process interruptions. In the scenario I ran, there was a
classic virtual link.
R1---------R2-------R3 connected via serial links
Area2....area1.....area0
All routers have loopbacks, which under the rules of the game have become
the RID's
There is also an external routing domain connecting R1 and R3 via the
ethernet ports. Redistribution is established, and works just fine.
When I severed the serial link between R2 and R3, the virtual link goes
down, and does not re-establish itself, even though the RID is being
advertised as a route into the exterior domain, and remains in the routing
tables of all routers as external routes.
I kinda expected this behaviour, but it still raises the question of the
supposed benefit of loopbacks as an interface that is "always up" and
therefore advantageous to use.
One of those "pitfalls" someone was asking about a couple of weeks back, I
suppose.
Chuck
----------------------
I am Locutus, a CCIE Lab Proctor. Xx_Brain_dumps_xX are futile. Your life as
it has been is over ( if you hope to pass ) From this time forward, you will
study US!
( apologies to the folks at Star Trek TNG )
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