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OSPF Routing loop?

 
 
Garry
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      04-23-2005
Somehow I must be going nuts ...

I'm trying to set up a backup link. Currently, all traffic on the
backbone is routed via OSPF-learned routes, which works fine. I have now
added a backup line, which is also OSPF enabled. "show ip ospf nei"
correctly shows all OSPF neighbors that should be there, none that
shouldn't. Network looks something like this (simplified):

R1----------R2
| |
| |
| |
R3----------R4

R1-R2 and R3-R4 are 100M LAN links, R1-R3 is a POS, R2-R4 a 2M link.

When R1-R3 goes down, it takes about three seconds for R1 to announce
the loss of OSPF neighbor to R2. R2 then adjusts its routing to use
R2-R4 for the link to the other side, and announces the routes. R1
accepts the routing changes - then, R2 switches back to using R1 as
gateway to the outside ... (whereas R1 still uses R2 as gateway to the
outside).

WTF is going on here? R1 is getting the route from R2, so why isn't R2
using what it's announcing instead of switching back to R1???

Hints appreciated!
 
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Ivan Ostres
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      04-23-2005
In article <d4eb63$ti6$(E-Mail Removed)>, http://www.velocityreviews.com/forums/(E-Mail Removed) says...
> When R1-R3 goes down, it takes about three seconds for R1 to announce
> the loss of OSPF neighbor to R2. R2 then adjusts its routing to use
> R2-R4 for the link to the other side, and announces the routes. R1
> accepts the routing changes - then, R2 switches back to using R1 as
> gateway to the outside ... (whereas R1 still uses R2 as gateway to the
> outside).
>
> WTF is going on here? R1 is getting the route from R2, so why isn't R2
> using what it's announcing instead of switching back to R1???
>


This looks interesting. Can you please post 'show ip ospf database' from
R1, R2 and R3 when POS link is down?

--
-Ivan.

*** Use Rot13 to see my eMail address ***
 
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Garry
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      04-23-2005
Ivan Ostres wrote:
> This looks interesting. Can you please post 'show ip ospf database' from
> R1, R2 and R3 when POS link is down?


Slightly longer dumps --- what excerpts would be the most interesting?
 
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Ivan Ostres
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      04-24-2005
In article <d4ejof$22$(E-Mail Removed)>, (E-Mail Removed) says...
> Ivan Ostres wrote:
> > This looks interesting. Can you please post 'show ip ospf database' from
> > R1, R2 and R3 when POS link is down?

>
> Slightly longer dumps --- what excerpts would be the most interesting?
>


How many areas do you have? Where do you get your "outside" routes? Do
you redistribute them? From where?


--
-Ivan.

*** Use Rot13 to see my eMail address ***
 
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Garry
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      05-07-2005
Ivan Ostres wrote:
> How many areas do you have? Where do you get your "outside" routes? Do
> you redistribute them? From where?


Just area 0.0.0.0 . Even tried adding IBGP on both routers with default
announced from the other side. Still can't seem to get the one router to
use the OSPF/BGP announced default route, but still sticks to the other
route ... the crazy thing I can't understand is that the router right
when the primary link goes down will use its backup connection,
announces it to the local OSPF network, then seems to get it back from
the other router and switches it over to the second even though its
default is back to him ...

What am I missing here?

-garry
 
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