Re: Redistribute a RIP default route into OSPF

Hi Jose,

In addition to the comment from Bob, you do have the ability to either:
a) Originate the default route always (default-information originate
always) - useful when you have a single Internet connection. With no
additional configuration options, the default route is advertised as
External Type 2 (E2) route with a metric 1;

b) Originate the default route dependent upon defined conditions
(default-information originate WITHOUT the always option) - which will
advertise an external default route into the OSPF domain only if the
advertising router has a non-OSPF default route in its routing table.
This is useful when you have two Internet connections, a default route
on each upstream router, e.g. ip route 0.0.0.0 0.0.0.0 Fa0/1. After
configuring conditional default route origination on both upstream
routers, they start announcing the default router as an E2 OSPF route
with metric 1. Since the external metrics are identical, each OSPF
router in the non-stub areas selects the closest exit point, resulting
in proximity-based load sharing. A downstream router with two equal-cost
paths towards the Internet will load balance between them;

c) In the previous examples there was no control on how to influence the
routing decision by a downstream router towards the Internet. However,
if you have a primary and backup datacenter, each with a connection to
the Internet you may require deterministic routing to occur. This is
where you can introduce metrics on the default routes advertised by the
two upstream routers. To change the metric of the OSPF default route,
use the metric-type and metric options of the default-information
originate command. The lowest cost wins. For example, on the primary
upstream router you might configure "default-information originate
metric 10" and on the secondary upstream router you might configure
"default-information originate metric 20". On both routers the same
default route to Fa0/1 is configured. Examining the OSPF database of any
downstream router will show both a Type 5 External link state from each
upstream router, however, the default route installed it its routing
table will be the default route to the primary upstream router;

d) The previous 3 examples are all very useful, but there are times when
you need to originate a default route into OSPF that is dependent on a
upstream route being installed in the routing table. Again, consider the
scenario of a primary and secondary datacenter presented in option 3,
where you have control but it is limited. The limitation is based on the
default route to Fa0/1. As long as this connection stays up/up then the
default route will be originated. With a dual homed connection to the
Internet, it is usual to use BGP from the provider(s) to each primary
and secondary upstream router. If the primary provider suffers a routing
failure within their network (of course this never happens :)) then you
will start black holing all internal traffic by forcing it up the link
to the primary provider, even though you have a perfectly good link from
your second provider in the secondary datacenter it will not be used. To
prevent black holes caused by failures in the upstream provider
infrastructure, both upstream routers should not advertise the default
route unconditionally, but only if they are receiving BGP routes from
the provider. The "default-information originate route-map" command
achieves this goal. Whenever a route in the IP routing table matches the
conditions specified in the route-map, the default route is advertised
into OSPF. You can use matches on IP prefixes, next-hops and metrics,
but not on BGP attributes such as AS-path or local preference (the
default-information originate route-map is quite limited).

There are other examples, such as Stub and Not-So-Stubby areas you can
research if interested.

Now I just hope I remember this during the lab :) (Cisco Lab 1 : Andy 0)

regards Andy

Bob Sinclair wrote:
> Jose,
>
> Actually, it is not possible to redistribute any default into OSPF, AFAIK.
> If there is a default in the forwarding table that you want to go into OSPF,
> then you would use the "default-information originate" command. With this
> command it is not necessary to do a "redistribution" command, and if you
> redistribute without "default-inf originate", then the redistribution will
> not work.
>
> -Bob
>
>
>> -----Original Message-----
>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>> Jose Luiz Marques Santana
>> Sent: Saturday, July 18, 2009 9:23 PM
>> To: ccielab_at_groupstudy.com
>> Subject: Redistribute a RIP default route into OSPF
>>
>> Hello GS,
>>
>> I have a doubt.
>> Is it possible redistribute a RIP default route into OSPF?
>> In my lab this configuration doesn't work.
>>
>> R1 fa1/9<----OSPF----->fa1/15 R2 Vlan57<-----RIP----->e0/1 R3
>>
>>
>> Configuration of R1
>> -------------------
>>
>> router ospf 1
>> router-id 10.4.4.4
>> log-adjacency-changes
>> area 34 range 10.0.0.0 255.0.0.0
>> network 10.4.4.4 0.0.0.0 area 34
>> network 163.1.0.4 0.0.0.0 area 0
>> network 163.1.0.134 0.0.0.0 area 0
>>
>>
>> R1# sh ip route ospf
>> 163.1.0.0/16 is variably subnetted, 5 subnets, 2 masks
>> O E2 163.1.57.0/24 [110/20] via 163.1.0.1, 01:35:28, FastEthernet1/9
>> O 163.1.3.0/24 [110/2] via 163.1.0.133, 01:35:28,
>> FastEthernet1/15
>> O E2 163.1.7.0/24 [110/20] via 163.1.0.1, 01:35:28, FastEthernet1/9
>> 10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
>> O IA 10.3.3.3/32 [110/2] via 163.1.0.133, 01:35:28, FastEthernet1/15
>> O 10.0.0.0/8 is a summary, 01:39:50, Null0
>> 150.1.0.0/24 is subnetted, 1 subnets
>> O E2 150.1.7.0 [110/20] via 163.1.0.1, 01:35:28, FastEthernet1/9
>>
>> R1#sh ip ospf neighbor
>>
>> Neighbor ID Pri State Dead Time Address
>> Interface
>> 10.3.3.3 1 FULL/BDR 00:00:39 163.1.0.133
>> FastEthernet1/15
>> 150.1.7.7 1 FULL/DR 00:00:33 163.1.0.1
>> FastEthernet1/9
>>
>>
>>
>> Configuration of R2
>> -------------------
>>
>> router ospf 1
>> router-id 150.1.7.7
>> log-adjacency-changes
>> redistribute rip subnets
>> network 163.1.0.1 0.0.0.0 area 0
>> distribute-list 10 in
>>
>> router rip
>> version 2
>> redistribute ospf 1 metric 1
>> passive-interface default
>> no passive-interface Vlan57
>> network 150.1.0.0
>> network 163.1.0.0
>> no auto-summary
>>
>> R2#sh ip route rip
>> R* 0.0.0.0/0 [120/1] via 163.1.57.5, 00:00:01, Vlan57
>>
>> R2#sh ip ospf neighbor
>>
>> Neighbor ID Pri State Dead Time Address
>> Interface
>> 10.4.4.4 1 FULL/BDR 00:00:35 163.1.0.4
>> FastEthernet1/15
>>
>>
>> Configuration of R3
>> -------------------
>>
>> router rip
>> version 2
>> passive-interface default
>> no passive-interface Ethernet0/1
>> no passive-interface Serial1/1
>> network 163.1.0.0
>> default-information originate
>> distribute-list prefix DEFAULT out Ethernet0/1
>> distance 109 0.0.0.0 255.255.255.255 RIP-ROUTES
>> no auto-summary
>>
>> !
>> ip prefix-list DEFAULT seq 5 permit 0.0.0.0/0
>>
>>
>> Warmest Regards,
>>
>>
>> ---
>> Jose Luiz
>>
>>
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>
>
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Received on Sun Jul 19 2009 - 11:32:46 ART