Re: OSPF Distance Command .!

It might be clearer for other people if you replied to my email about
that topology. When you are testing OSPF I recommend you shut interfaces
between all routers before clearing the process on each. Otherwise, in
many instances you can see very different behaviour (especially with
external routes).

I do not know if the behviour which I see in my lab applies to all
releases, which was why I included the IOS version and router model.
Perhaps it is different, perhaps not. The version of IOS you are using
may contain a bug, perhaps mine does. Try the same release as me if you
wish to like: c7200-k91p-mz.122-25.S15. The point is that selection of
external routes follows very different rules to that of internal routes,
and you don't need to take my word for it as the rfc's contains the details.

Paul.

Divin Mathew John wrote:
> Paul Cosgrove,
>
> I tried your topology..
> R3
> / \
> R1 R2
> \ /
> R0
>
> R3 does not run any routing protocols, but has Lo0: 3.3.3.3 for testing.
> R1 and R2 both have static routes to R3's loopback.
> R0, R1 and R2 run OSPF between each other.
>
> this is my config
> ***********************
> R0********************
> ***********************
> interface Loopback0
> ip address 100.100.100.100 255.255.255.0
> !
> interface Serial0/0
> ip address 10.1.1.1 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/1
> ip address 20.1.1.1 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/2
> no ip address
> shutdown
> serial restart-delay 0
> !
> interface Serial0/3
> no ip address
> shutdown
> serial restart-delay 0
> !
> router ospf 1
> router-id 100.100.100.100
> log-adjacency-changes
> network 10.1.1.1 0.0.0.0 area 0
> network 20.1.1.1 0.0.0.0 area 0
> network 100.100.100.100 0.0.0.0 area 0
> !
> ip http server
> ip forward-protocol nd
> !
>
> ***********************
> R1********************
> ***********************
> interface Loopback0
> ip address 1.1.0.1 255.255.255.0
> !
> interface Serial0/0
> ip address 10.1.1.2 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/1
> ip address 13.1.1.1 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/2
> no ip address
> shutdown
> serial restart-delay 0
> !
> interface Serial0/3
> no ip address
> shutdown
> serial restart-delay 0
> !
> router ospf 1
> router-id 1.1.0.1
> log-adjacency-changes
> redistribute static subnets
> network 1.1.0.1 0.0.0.0 area 0
> network 10.1.1.2 0.0.0.0 area 0
> !
> ip http server
> ip forward-protocol nd
> ip route 3.3.0.3 255.255.255.255 Serial0/1 13.1.1.2
> !
> ***********************
> R2********************
> ***********************
> interface Loopback0
> ip address 2.2.0.2 255.255.255.0
> !
> interface Serial0/0
> ip address 20.1.1.2 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/1
> ip address 23.1.1.1 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/2
> no ip address
> shutdown
> serial restart-delay 0
> !
> interface Serial0/3
> no ip address
> shutdown
> serial restart-delay 0
> !
> router ospf 1
> router-id 2.2.0.2
> log-adjacency-changes
> redistribute static subnets
> network 2.2.0.2 0.0.0.0 area 0
> network 20.1.1.2 0.0.0.0 area 0
> !
> ip http server
> ip forward-protocol nd
> ip route 3.3.0.3 255.255.255.255 Serial0/1 23.1.1.2
> !
> ***********************
> R3********************
> ***********************
> !
> interface Loopback0
> ip address 3.3.0.3 255.255.255.0
> !
> interface Serial0/0
> ip address 13.1.1.2 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/1
> ip address 23.1.1.2 255.255.255.252
> serial restart-delay 0
> !
> interface Serial0/2
> no ip address
> shutdown
> serial restart-delay 0
> !
> interface Serial0/3
> no ip address
> shutdown
> serial restart-delay 0
> !
> ip http server
> ip forward-protocol nd
> !
> !
> !
>
> and this is my routing table at R0
> R0#sir
> Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
> D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> E1 - OSPF external type 1, E2 - OSPF external type 2
> i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
> ia - IS-IS inter area, * - candidate default, U - per-user static
> route
> o - ODR, P - periodic downloaded static route
>
> Gateway of last resort is not set
>
> 1.0.0.0/32 is subnetted, 1 subnets
> O 1.1.0.1 [110/65] via 10.1.1.2, 00:00:01, Serial0/0
> 2.0.0.0/32 is subnetted, 1 subnets
> O 2.2.0.2 [110/65] via 20.1.1.2, 00:00:01, Serial0/1
> 100.0.0.0/24 is subnetted, 1 subnets
> C 100.100.100.0 is directly connected, Loopback0
> 3.0.0.0/32 is subnetted, 1 subnets
> O E2 3.3.0.3 [110/20] via 20.1.1.2, 00:00:01, Serial0/1
> [110/20] via 10.1.1.2, 00:00:01, Serial0/0
> 20.0.0.0/30 is subnetted, 1 subnets
> C 20.1.1.0 is directly connected, Serial0/1
> 10.0.0.0/30 is subnetted, 1 subnets
> C 10.1.1.0 is directly connected, Serial0/0
>
> It does Load balancing.!
>
> R0#show ip ospf neighbor
>
> Neighbor ID Pri State Dead Time Address Interface
> 1.1.0.1 0 FULL/ - 00:00:38 10.1.1.2 Serial0/0
> 2.2.0.2 0 FULL/ - 00:00:34 20.1.1.2 Serial0/1
>
> i did try shutting interafces... clear ip route * , clear ip ospf process
>
> no change in the OUTcome.!
>
> Thanking You
>
> Yours Sincerely
>
> Divin Mathew John
> divinjohn_at_gmail.com
> divin_at_dide3d.com
> http://www.dide3d.com
> +91 9945430983
> +91 9846697191
> +974 5008916
> PGP PUBLIC KEY BLOCK @ http://www.dide3d.com/divin_Public_PGP_key.txt
> Sent from Bangalore, KA, India
>
> On Fri, May 22, 2009 at 8:59 PM, Paul Cosgrove <paul.cosgrove_at_gmail.com>wrote:
>
>
>> Hi Sadiq,
>>
>> I would have to recommend trying it again yourself, as it does work:
>>
>> R1 ----- R2
>> \ /
>> \ /
>> \ /
>> R0
>>
>> All links are network type point to point. Shutdown interfaces, cleared
>> ospf process, no shut and waited for neighbors to establish.
>>
>> R0 then shows the following:
>>
>> Gateway of last resort is not set
>>
>> O 192.168.12.0/24 [110/128] via 192.168.20.2, 00:00:58, Serial1/1
>> [110/128] via 192.168.10.1, 00:00:58, Serial1/0
>> 1.0.0.0/32 is subnetted, 1 subnets
>> O 1.1.1.1 [110/65] via 192.168.10.1, 00:00:58, Serial1/0
>> 2.0.0.0/32 is subnetted, 1 subnets
>> O 2.2.2.2 [110/65] via 192.168.20.2, 00:00:58, Serial1/1
>> C 192.168.10.0/24 is directly connected, Serial1/0
>> C 192.168.20.0/24 is directly connected, Serial1/1
>> 10.0.0.0/32 is subnetted, 1 subnets
>> C 10.10.10.10 is directly connected, Loopback0
>>
>> R0(config)#access-list 10 permit 192.168.12.0
>> R0(config)#router ospf 1
>> R0(config-router)#distance 90 1.1.1.1 0.0.0.0 10
>> R0(config-router)#do sh ip ro
>> Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
>> D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
>> N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
>> E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
>> i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
>> ia - IS-IS inter area, * - candidate default, U - per-user static
>> route
>> o - ODR, P - periodic downloaded static route
>>
>> Gateway of last resort is not set
>>
>> O 192.168.12.0/24 [90/128] via 192.168.10.1, 00:00:05, Serial1/0
>> 1.0.0.0/32 is subnetted, 1 subnets
>> O 1.1.1.1 [110/65] via 192.168.10.1, 00:00:05, Serial1/0
>> 2.0.0.0/32 is subnetted, 1 subnets
>> O 2.2.2.2 [110/65] via 192.168.20.2, 00:00:05, Serial1/1
>> C 192.168.10.0/24 is directly connected, Serial1/0
>> C 192.168.20.0/24 is directly connected, Serial1/1
>> 10.0.0.0/32 is subnetted, 1 subnets
>> C 10.10.10.10 is directly connected, Loopback0
>> R0(config-router)#
>>
>> AD can and is often used to differentiate routes in the same protocol.
>> EIGRP externals and BGP internal routes being some obvious examples.
>> Paul.
>>
>>
>>
>> Sadiq Yakasai wrote:
>>
>>
>>> Gents, a little search over GS archives would second Bryan's point! This
>>> issue hunted me down in my first attempt!
>>>
>>> While some have even gone to TAC, others have tried bugging it! But from
>>> the
>>> research I carried out a while ago, my conclusion is you are not to use AD
>>> to influence prefix selection WITHIN the same routing protocol - use
>>> metric
>>> instead! BETWEEN 2 or more routing protocols, use AD.
>>>
>>> Otherwise, you are in for a long, unreliable and incoherent exercise.
>>>
>>> Sadiq
>>>
>>> On Fri, May 22, 2009 at 3:23 PM, Bryan Bartik <bbartik_at_ipexpert.com>
>>> wrote:
>>>
>>>
>>>
>>>
>>>> Hello,
>>>>
>>>> Divin, I think you hit it right on :) I have labbed this several times
>>>> before and what I found was that you cannot use AD to prefer one ospf
>>>> route
>>>> over another in the same ospf process (There may be crazy scenarios where
>>>> you can, but I don't recall finding any). Makes sense, since like you
>>>> said
>>>> AD is to prefer one protocol over another. You could place the link to R1
>>>> in
>>>> another process on R0 and then change the distance in that process.
>>>>
>>>> Bryan Bartik
>>>> CCIE #23707 (R&S), CCNP
>>>> Sr. Support Engineer - IPexpert, Inc.
>>>> URL: http://www.IPexpert.com
>>>>
>>>>
>>>> Blogs and organic groups at http://www.ccie.net
>>>>
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Received on Fri May 22 2009 - 17:07:02 ART