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

Hi ccie99999,

Thank you for bringing up a nice topic. Just a slight confirmation from
your end as I am little confused at this point , what ever you are trying
to modify would actually modify the Master Table and not the Ospf DB , is
it right ? or is there a way to change the ospf prefix type from IA to O
only with the route-maps or some sort of filtering?

Thank you
Rakesh M

On Tue, Jan 8, 2013 at 7:58 PM, Jay McMickle <jay.mcmickle_at_yahoo.com> wrote:

> Not to pick sides, but whether or not this was a copy and paste from a
> workbook, I didn't see Narbik selling workbooks here. I thought it helped
> as it did help me remember these points. I don't work with OSPF so I find
> these useful.
>
> Now, had he mentioned "that all of this can be found on my workbooks", I
> would have thought that to be out of bounds.
>
> Regards,
> Jay McMickle- CCIE #35355 (RS)
> Sent from my iPhone 5
>
> On Jan 8, 2013, at 12:30 AM, Brian McGahan <bmcgahan_at_ine.com> wrote:
>
> > Hi Narbik,
> >
> > I would argue that your response is spam, and is not
> > applicable to the list. Once again you are posting out of context "free
> lab"
> > material without answering the original poster's question. I could
> likewise
> > post output from INE's lab workbooks or from Cisco's documentation but
> that is
> > not productive. If you have technology discussion input to give we are
> more
> > than happy to accept it.
> >
> > Thanks,
> >
> > Brian McGahan, CCIE #8593 (R&S/SP/Security)
> > bmcgahan_at_INE.com<mailto:bmcgahan_at_INE.com>
> >
> > Internetwork Expert, Inc.
> > http://www.INE.com
> >
> > From: Narbik Kocharians [mailto:narbikk_at_gmail.com]
> > Sent: Monday, January 07, 2013 11:15 PM
> > To: ccie99999
> > Cc: Brian McGahan; Carlos G Mendioroz; Cisco certification
> > Subject: Re: preferring OSPF inter-area compared to intra-area
> >
> > SORRY FOR THE LONG POST.
> >
> > Let's 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(S0/0.21)R2>
> > 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(S0/0.31)R3>
> > 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(S0/0.41)R4>
> >
> > R2 is running OSPF on its Lo0 and Lo1 with IP addresses of
> > 2.2.2.2/8<http://2.2.2.2/8> and 200.2.2.2/24<http://200.2.2.2/24>
> > respectively.
> >
> > R3 is running ospf on its Lo0 with an IP address of
> > 3.3.3.3/8<http://3.3.3.3/8>
> > R4 is running ospf on its Lo0 with an IP address of
> > 4.4.4.4/8<http://4.4.4.4/8>
> >
> > Everything is running in OSPF area 0. Let's begin:
> >
> > On R1
> >
> > R1#Show ip route ospf | I O
> > O 2.0.0.0/8<http://2.0.0.0/8> [110/65] via 12.1.1.2, 00:01:24,
> > Serial0/0.12
> > O 3.0.0.0/8<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:44,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:14,
> > Serial0/0.14
> > O 200.2.2.0/24<http://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
> > 2.0.0.0/8<http://2.0.0.0/8> and 200.2.2.0/24<http://200.2.2.0/24>.
> >
> > Let's 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<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:38,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:38,
> > Serial0/0.14
> >
> > Let's remove the previous solution and filter network
> > 2.0.0.0/8<http://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<http://2.0.0.0/8> [110/65] via 12.1.1.2, 00:00:19,
> > Serial0/0.12
> > O 3.0.0.0/8<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:19,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:19,
> > Serial0/0.14
> > O 200.2.2.0/24<http://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
> > 2.0.0.0/8<http://2.0.0.0/8> coming 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<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:23,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:23,
> > Serial0/0.14
> > O 200.2.2.0/24<http://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.
> >
> > Let's remove the configuration from the previous solution and filter
> network
> > 200.2.2.0/24<http://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<http://2.0.0.0/8> [110/65] via 12.1.1.2, 00:00:29,
> > Serial0/0.12
> > O 3.0.0.0/8<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:29,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:29,
> > Serial0/0.14
> > O 200.2.2.0/24<http://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<http://2.0.0.0/8> [110/65] via 12.1.1.2, 00:00:05,
> > Serial0/0.12
> > O 3.0.0.0/8<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:05,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:05,
> > Serial0/0.14
> >
> > Now....let's 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<http://2.0.0.0/8> [110/65] via 12.1.1.2, 00:00:34,
> > Serial0/0.12
> > O 3.0.0.0/8<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:34,
> > Serial0/0.13
> > O 4.0.0.0/8<http://4.0.0.0/8> [110/65] via 14.1.1.4, 00:00:34,
> > Serial0/0.14
> > O 200.2.2.0/24<http://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<http://2.0.0.0/8> [110/65] via 12.1.1.2, 00:00:06,
> > Serial0/0.12
> > O 3.0.0.0/8<http://3.0.0.0/8> [110/65] via 13.1.1.3, 00:00:06,
> > Serial0/0.13
> > O 4.0.0.0/8<http://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<mailto: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<mailto: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
> >
> >
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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
> >
> >
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