Re: preferring OSPF inter-area compared to intra-area

So, yesterday I was in trouble because of 2 different errors:

1st:

I was claiming to make a route-map, matching the prefix with an acl + the
ip source-route but I was incorrectly using the source-route.. I was using
the SW1 ospf id.. and instead I got to use the R3 ospf id.. for that
reason, the route-map was not filtering at all.
I just lab it using Narbik's example and I was able to filter it.

2nd:
Once I was able to filter (yesterday at the end, I've used a route-map
matching only the prefix), I was expecting the ospf to be able to see an
alternative path using the inter-area path. Here again I was wrong since I
was filtering RIB.. (I cannot filter type1 and type2 of course).. Brian was
able to point me to the simple fact that I cannot filter RIP and claim OSPF
change is decision..
Process is: I read my LSAs, I do a SPF process and I do generate RIB. If my
RIB is filtering by something I cannot pretend OSPF knows that.
For this reason, this page here of the doc cd is not correct
http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_ospf/configuration/12-4t/
iro-inbound.html

Then, at the end.. Thanks Narbik for your help on 1st point.. and thanks
Brian for your help on 2nd one!
You have seen each one a different error/perspective in my config and with
you both I was able to understand where I was wrong.
You guys are awesome!

On Tue, Jan 8, 2013 at 8:19 AM, ccie99999 <ccie99999_at_gmail.com> wrote:

> Narbik,
> try to link R2 fa0/0 to R3 fa0/0 and put them in area 1
> what I was trying to do, the thing that triggered this thread, was to
> reach R2 L0 from R1 but through R3.
> According to Brian this is not possible..since I'm preferring inter-area
> instead of intra-area. With a route-map I'm going to filter RIB.
> If I've understood well I can filter RIB as much as I can but OSPF won't
> change his decision.
> I should filter ospf db instead, but this is not possibile since I'm in
> the same area and I have lsa type1 and type2.
>
> easiest workaround for sure is move the loopback 0 from area 1 to area 0.
>
> did I write something not correct? am I in the correct path now?
>
>
>
> On Tue, Jan 8, 2013 at 5:14 AM, Narbik Kocharians <narbikk_at_gmail.com>wrote:
>
>> *SORRY FOR THE LONG POST.*
>>
>> *
>> *
>>
>> *Lets say we have a hub and spoke topology, where R1 is the hub router,
>> and R2, R3, and R4 are the spoke routers. All the links are configured as
>> P2P using the following IP addressing scheme:*
>>
>>
>>
>>
R1(S0/0.12)12.1.1.1/24--------------12.1.1.2(S0/0.21)R2<http://12.1.1.1/24---
-----------12.1.1.2%28S0/0.21%29R2>
>>
>>
R1(S0/0.13)13.1.1.1/24--------------13.1.1.3(S0/0.31)R3<http://13.1.1.1/24---
-----------13.1.1.3%28S0/0.31%29R3>
>>
>>
R1(S0/0.14)14.1.1.1/24--------------14.1.1.4(S0/0.41)R4<http://14.1.1.1/24---
-----------14.1.1.4%28S0/0.41%29R4>
>>
>>
>>
>> *R2 is running OSPF on its Lo0 and Lo1 with IP addresses of 2.2.2.2/8and
>> 200.2.2.2/24 respectively.*
>>
>> * *
>>
>> *R3 is running ospf on its Lo0 with an IP address of 3.3.3.3/8*
>>
>> *R4 is running ospf on its Lo0 with an IP address of 4.4.4.4/8*
>>
>> * *
>>
>> *Everything is running in OSPF area 0. Lets begin:*
>>
>>
>>
>> *On R1*
>>
>>
>>
>> R1#Show ip route ospf | I O
>>
>> *O 2.0.0.0/8 [110/65] via 12.1.1.2, 00:01:24, Serial0/0.12*
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:44, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:14, Serial0/0.14
>>
>> *O 200.2.2.0/24 [110/65] via 12.1.1.2, 00:01:24, Serial0/0.12*
>>
>>
>>
>> *You can see that R1 is receiving two routes from R2, networks
2.0.0.0/8and
>> 200.2.2.0/24.*
>>
>>
>>
>> *Lets filter all routes coming through S0/0.12:*
>>
>>
>>
>> *On R1*
>>
>>
>>
>> R1(config)#*Route-map tst deny 10*
>>
>> R1(config-route-map)#*match interface s0/0.12*
>>
>> R1(config)#*route-map tst permit 90*
>>
>>
>>
>> R1(config-route-map)#*router ospf 1*
>>
>> R1(config-router)#*distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:38, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:38, Serial0/0.14
>>
>>
>>
>> *Lets remove the previous solution and filter network 2.0.0.0/8 coming
>> through S0/0.21 sub-interface:*
>>
>>
>>
>> R1(config)#*No route-map tst*
>>
>>
>>
>> R1(config)#*router ospf 1*
>>
>> R1(config-router)#*No distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 2.0.0.0/8 [110/65] via 12.1.1.2, 00:00:19, Serial0/0.12
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:19, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:19, Serial0/0.14
>>
>> O 200.2.2.0/24 [110/65] via 12.1.1.2, 00:00:19, Serial0/0.12
>>
>>
>>
>> *The previous solution will NOT work here; to filter network
2.0.0.0/8coming through S0/0.21 we need to do the following:
>> *
>>
>>
>>
>> R1(config)#*access-list 2 permit 2.0.0.0 0.255.255.255*
>>
>>
>>
>> R1(config)#*route-map tst deny 10*
>>
>> R1(config-route-map)#*match interface s0/0.12*
>>
>> R1(config-route-map)#*match ip addr 2*
>>
>> R1(config)#*route-map tst permit 90*
>>
>>
>>
>> R1(config-route-map)#*router ospf 1*
>>
>> R1(config-router)#*distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:23, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:23, Serial0/0.14
>>
>> O 200.2.2.0/24 [110/65] via 12.1.1.2, 00:00:23, Serial0/0.12
>>
>>
>>
>> *Perfect it worked, obviously the same task can be configured using
>> another method.*
>>
>> * *
>>
>> *Lets remove the configuration from the previous solution and filter
>> network 200.2.2.0/24 coming from R2, but this time we are going to use
>> the IP Next-hop option:*
>>
>>
>>
>> R1(config)#*No route-map tst*
>>
>> R1(config)#*No access-list 2*
>>
>>
>>
>> R1(config)#*router ospf 1*
>>
>> R1(config-router)#*No distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 2.0.0.0/8 [110/65] via 12.1.1.2, 00:00:29, Serial0/0.12
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:29, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:29, Serial0/0.14
>>
>> O 200.2.2.0/24 [110/65] via 12.1.1.2, 00:00:29, Serial0/0.12
>>
>>
>>
>> *To filter using the IP next-hop option:*
>>
>>
>>
>>
>>
>> R1(config)#*access-list 1 permit 200.2.2.0 0.0.0.255*
>>
>>
>>
>> R1(config)#*access-list 10 permit host 12.1.1.2*
>>
>>
>>
>> R1(config)#*route-map tst deny 10*
>>
>> R1(config-route-map)#*match ip addr 1*
>>
>> R1(config-route-map)#*match ip next-hop 10*
>>
>> R1(config)#*route-map tst permit 90*
>>
>>
>>
>> R1(config-route-map)#*router ospf 1*
>>
>> R1(config-router)#*distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 2.0.0.0/8 [110/65] via 12.1.1.2, 00:00:05, Serial0/0.12
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:05, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:05, Serial0/0.14
>>
>> * *
>>
>> *Now.lets remove the previous solution and use the route-source
>> option:*
>>
>>
>>
>> R1(config)#*No access-list 1*
>>
>> R1(config)#*No access-list 10*
>>
>> R1(config)#*No route-map tst*
>>
>> R1(config)#*router ospf 1*
>>
>> R1(config-router)#*No distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 2.0.0.0/8 [110/65] via 12.1.1.2, 00:00:34, Serial0/0.12
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:34, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:34, Serial0/0.14
>>
>> O 200.2.2.0/24 [110/65] via 12.1.1.2, 00:00:34, Serial0/0.12
>>
>>
>>
>> * *
>>
>> *To use the route-source option, we MUST use the RID of R2 in the
>> access-list. To find out the RID of R2:*
>>
>>
>>
>> R2#*Show ip ospf | I ID*
>>
>> *Routing Process "ospf 1" with ID 0.0.0.2*
>>
>>
>>
>> R1(config)#*access-list 3 permit 0.0.0.2*
>>
>> R1(config)#*access-list 30 permit 200.2.2.0 0.0.0.255*
>>
>>
>>
>> R1(config)#*route-map tst deny 10*
>>
>> R1(config-route-map)#*match ip addr 30*
>>
>> R1(config-route-map)#*match ip route-source 3*
>>
>> R1(config)#*route-map tst permit 90*
>>
>> R1(config-route-map)#*router ospf 1*
>>
>> R1(config-router)#*distribute-list route-map tst in*
>>
>>
>>
>> R1#*Show ip route ospf | I O*
>>
>> O 2.0.0.0/8 [110/65] via 12.1.1.2, 00:00:06, Serial0/0.12
>>
>> O 3.0.0.0/8 [110/65] via 13.1.1.3, 00:00:06, Serial0/0.13
>>
>> O 4.0.0.0/8 [110/65] via 14.1.1.4, 00:00:06, Serial0/0.14
>>
>>
>>
>>
>>
>> I hope this helped.
>>
>> On Mon, Jan 7, 2013 at 7:09 PM, ccie99999 <ccie99999_at_gmail.com> wrote:
>>
>>> Thanks for your reply Brian..
>>>
>>> I see your point about filtering the RIB and not what OSPF chooses. ( I
>>> didn't realize this before actually)
>>>
>>> What I was complaining is that route-map matching ip next-hop or matching
>>> ip route-source is not working when applied with a distribute list
>>> inbound
>>> to ospf.
>>> Strange I don't find any official reference on this scenario.
>>>
>>>
>>> On Mon, Jan 7, 2013 at 6:08 PM, Brian McGahan <bmcgahan_at_ine.com> wrote:
>>>
>>> > This filters the RIB (routing table), not the OSPF decision process. By
>>> > the time you apply this OSPF has already chosen the intra area route
>>> over
>>> > the inter area one, so all you can do is permit or deny the intra area
>>> one.
>>> >
>>> > The only way to really accomplish this is to make the two route types
>>> > equal. If you were to change the inter area route to intra area with
>>> > something like a virtual link or tunnel then you can modify which path
>>> is
>>> > preferred.
>>> >
>>>
>>>
>>>
>>> --
>>> @ccie99999
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
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>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> --
>> *Narbik Kocharians
>> *CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>> *www.MicronicsTraining.com* <http://www.micronicstraining.com/>
>> Sr. Technical Instructor
>> YES! We take Cisco Learning Credits!
>> A Cisco Learning Partner
>>
>
>
>
> --
> @ccie99999
>

--
@ccie99999
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