RE: OSPF LSA type 3 filtering

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So that is what I read the 34,332 posts about workbooks, 9,810 posts about Pakistan schools and 5,641 posts about lab questions to learn...

Carry on gents!

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Brian McGahan
Sent: Wednesday, January 02, 2013 10:28 PM
To: Narbik Kocharians
Cc: Cisco certification
Subject: RE: OSPF LSA type 3 filtering

Sure. Reachability information means the actual prefixes being advertised, like 10.0.0.0/8, 1.2.3.4/32, etc. Topology information means the graph of connectivity within the area that affects the SPF calculation. SPF runs to find the shortest path between nodes, not between prefixes. This is why in OSPFv3 the definition of topology information and reachability information was further separated into Link LSAs and Intra-area Prefix LSAs.

In OSPFv2 you can see this from the output of the database:

Rack1SW3#show ip ospf database

            OSPF Router with ID (150.1.9.9) (Process ID 1)

                Router Link States (Area 2)

Link ID ADV Router Age Seq# Checksum Link count
150.1.3.3 150.1.3.3 660 0x80000051 0x0061BB 1
150.1.6.6 150.1.6.6 1019 0x80000050 0x00D8F7 1
150.1.7.7 150.1.7.7 894 0x80000055 0x0005C0 5
150.1.9.9 150.1.9.9 670 0x8000004F 0x00B13F 2

                Net Link States (Area 2)

Link ID ADV Router Age Seq# Checksum
155.1.37.3 150.1.3.3 660 0x8000004E 0x0082C4
155.1.67.6 150.1.6.6 1019 0x8000004E 0x002BEE
155.1.79.9 150.1.9.9 671 0x8000004E 0x009A64

The Type 1 Router LSAs contain the information about the links, such as their addresses and costs, along with adjacencies. Type 2 LSAs just contain the information to simplify the SPF calculation on broadcast and non-broadcast networks by making the adjacency look like hub and spoke as opposed to full mesh. This way you calculate your SPF cost to the DR and it implicitly means you've calculated the SPF cost to all the DR's attached neighbor's on the segment. This is why the "Router Link States" above show the "Link count" but the "Net Link States" don't, because Type 2 LSA doesn't represent the reachability information, it represents the topology.

Topology information is summarized in OSPF by defining areas. A router in Area 0 does not run SPF end-to-end to reach a router in Area 1. This is by design and by default. By defining areas you don't need to know the entire graph of the topology end-to-end. Reachability information however is not summarized by default in OSPF, and is what the "area range" or "summary-address" commands do. Hence LSA 2 doesn't have anything to do with "area range" "summary-address" or "area filter" because topology information is summarized regardless as soon as you define areas.

Brian McGahan, CCIE #8593 (R&S/SP/Security) bmcgahan_at_INE.com

Internetwork Expert, Inc.
http://www.INE.com

From: Narbik Kocharians [mailto:narbikk_at_gmail.com]
Sent: Wednesday, January 02, 2013 9:01 PM
To: Brian McGahan
Cc: Cisco certification
Subject: Re: OSPF LSA type 3 filtering

I don't understand where you are going with this, can you show me on IOS what you are talking about so we can eliminate any misunderstanding, NOT theory, on IOS. But if you don't like the LSA type-2 addition to what we were talking about, just remove it.

On Wed, Jan 2, 2013 at 6:55 PM, Brian McGahan <bmcgahan_at_ine.com> wrote:
Do you mean summarizing topology information or reachability information? Topology information is already automatically summarized at the ABR, and Type 2 LSA doesn't contain any reachability information, so I'm not sure what you're referring to.

Brian McGahan, CCIE #8593 (R&S/SP/Security) bmcgahan_at_INE.com

Internetwork Expert, Inc.
http://www.INE.com

From: Narbik Kocharians [mailto:narbikk_at_gmail.com]
Sent: Wednesday, January 02, 2013 8:51 PM
To: Brian McGahan
Cc: Cisco certification

Subject: Re: OSPF LSA type 3 filtering

What if in area 1 there are some LSA type-1 and type-2? Can you not filter them or summarize them with the "area range" command?
On Wed, Jan 2, 2013 at 6:17 PM, Brian McGahan <bmcgahan_at_ine.com> wrote:
How does it affect Type 2 LSAs?

Brian McGahan, CCIE #8593 (R&S/SP/Security) bmcgahan_at_INE.com

Internetwork Expert, Inc.
http://www.INE.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Narbik Kocharians
Sent: Wednesday, January 02, 2013 4:52 PM
To: Tim Cribbs Jr.
Cc: Sarad; Cisco certification
Subject: Re: OSPF LSA type 3 filtering

Thanks very much, I am glad it helped. And yes it also handles LSA type-2.

On Wed, Jan 2, 2013 at 2:28 PM, Tim Cribbs Jr. <tmcribbs_at_gmail.com> wrote:

> I was JUST at this exact point in my studies and was about to comment,
> but THANKFULLY Narbik got to it before me. lol
>
> BTW, area range will also work with type 2 (1&2).
>
> Tim
>
> On Wed, Jan 2, 2013 at 5:05 PM, Sarad <tosara_at_gmail.com> wrote:
> > Hi Narbik,
> >
> > Thanks for the in detailed expert level explanation. People like you
> > keep this forum alive. I just did a lab on this and now it make more
> > sense. So take out from this would be both these commands do the LSA
> > filtering on
> ABR
> > but Area range command would work only when filtering LSA type 1
> > regenerating as type 3.
> >
> >
> > Area-range
> >
> > LSA1 ---> LSA3
> >
> > Filter-list
> >
> > LSA1/LSA3 -----> LSA
> >
> >
> > Thanks again for the awesome explanation.
> >
> > Cheers
> > Sara
> >
> >
> > On Thu, Jan 3, 2013 at 7:49 AM, Narbik Kocharians
> > <narbikk_at_gmail.com>
> wrote:
> >
> >> *Sarad,*
> >> *Since we are all engineers, and engineers are "Must See" people,
> >> walk through the following lab.*
> >> **
> >> *Let s assume the following topology:*
> >>
> >>
> >>
> >> Lo0(1.1.1.1/24)----- *R1*(F0/0)12.1.1.1/24 --------
> 12.1.1.2/24(F0/0)*R2*
> >>
> >>
> >>
> >> *R2*(S0/0.23) 23.1.1.2/24----------23.1.1.3/24(S0/0.32) *R3*
> >>
> >>
> >>
> >> *R3*(F0/0)34.1.1.3/24--------34.1.1.4/24(F0/0)*R4*
> >>
> >>
> >>
> >> *OSPF Areas configuration:*
> >>
> >> R1 s Lo0 is advertised with a mask of 24 in area 1
> >>
> >> The link connecting R1 to R2 is in area 1
> >>
> >> The link connecting R2 to R3 is in area 0
> >>
> >> The link connecting R3 to R4 is in area 2
> >>
> >>
> >>
> >> *To verify:*
> >>
> >> R1#*Show ip route ospf | I O*
> >>
> >> O IA 34.1.1.0 [110/66] via 12.1.1.2, 00:04:13, FastEthernet0/0
> >>
> >> O IA 23.1.1.0 [110/65] via 12.1.1.2, 00:04:13, FastEthernet0/0
> >>
> >>
> >>
> >> R2#*Show ip route ospf | I O*
> >>
> >> O IA 34.1.1.0 [110/65] via 23.1.1.3, 00:05:05, Serial0/0.23
> >>
> >> O 1.1.1.0 [110/2] via 12.1.1.1, 00:04:35, FastEthernet0/0
> >>
> >>
> >>
> >> R3#*Show ip route ospf | I O*
> >>
> >> O IA 1.1.1.0 [110/66] via 23.1.1.2, 00:04:30, Serial0/0.32
> >>
> >> O IA 12.1.1.0 [110/65] via 23.1.1.2, 00:05:05, Serial0/0.32
> >>
> >>
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> O IA 1.1.1.0 [110/67] via 34.1.1.3, 00:04:30, FastEthernet0/0
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:04:30, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:04:30, FastEthernet0/0
> >>
> >>
> >>
> >> *Let s test the "area range" command on R3:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3(config)#*router ospf 1*
> >>
> >> R3(config-router)#*area 1 range 1.1.1.0 255.255.255.0 not-ad*
> >>
> >>
> >>
> >> *To verify the configuration:*
> >>
> >> **
> >>
> >> *On R4*
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> *O IA 1.1.1.0 [110/67] via 34.1.1.3, 00:07:07, FastEthernet0/0*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:07:07, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:07:07, FastEthernet0/0
> >>
> >>
> >> *NOTE: It did not work, because the Area range command does not
> >> work on inter-area routes at all; now let s try this command on
> >> R2:*
> >> **
> >>
> >> *On R2*
> >>
> >> R2(config)#*router ospf 1*
> >>
> >> R2(config-router)#*area 1 range 1.1.1.0 255.255.255.0 not-ad*
> >>
> >>
> >>
> >> *To verify the configuration:*
> >> **
> >> *On** R2*
> >>
> >> *NOTE: It s in the routing table and the database of the local
> >> router
> >> (R2):*
> >>
> >>
> >>
> >> R2#*sh ip route ospf | I O*
> >>
> >> O IA 34.1.1.0 [110/65] via 23.1.1.3, 00:00:33, Serial0/0.23
> >>
> >> *O 1.1.1.0 [110/2] via 12.1.1.1, 00:00:33, FastEthernet0/0*
> >>
> >>
> >>
> >> R2#*Show ip ospf da router*
> >>
> >>
> >>
> >> *Link connected to: a Stub Network*
> >>
> >> * (Link ID) Network/subnet number: 1.1.1.0*
> >>
> >> * (Link Data) Network Mask: 255.255.255.0*
> >>
> >> * Number of TOS metrics: 0*
> >>
> >> * TOS 0 Metrics: 1*
> >>
> >> * *
> >>
> >> *But is it going to be advertised to the other areas? Let s check:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3#*Show ip route ospf | I O*
> >>
> >> O IA 12.1.1.0 [110/65] via 23.1.1.2, 00:07:49, Serial0/0.32
> >>
> >>
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:18:52, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:09:14, FastEthernet0/0
> >>
> >>
> >>
> >> *As you can see the answer is "NO". *
> >>
> >> *So you can see that it prevented the LSA type-3 generation for the
> >> 1.1.1.0/24 prefix on the router that sees the route as LSA-1 and
> LSA-3. *
> >>
> >> * *
> >>
> >> *NOW .let s test the area filter-list , but before we test it, we
> should
> >> remove the Area range command:*
> >>
> >> **
> >>
> >> *On R2*
> >>
> >> R2(config)#*router ospf 1*
> >>
> >> R2(config-router)#*No area 1 range 1.1.1.0 255.255.255.0
> >> not-advertise*
> >>
> >>
> >>
> >> *To verify the configuration:*
> >>
> >> **
> >>
> >> *On R3*
> >>
> >>
> >>
> >> R3#*Show ip route ospf | I O*
> >>
> >> *O IA 1.1.1.0 [110/66] via 23.1.1.2, 00:00:16, Serial0/0.32*
> >>
> >> O IA 12.1.1.0 [110/65] via 23.1.1.2, 00:12:47, Serial0/0.32
> >>
> >>
> >>
> >> *Let s configure the area filter-list on R2:*
> >>
> >> * *
> >>
> >> *On R2*
> >>
> >> R2(config)#*IP prefix-list tst deny 1.1.1.0/24*
> >>
> >> R2(config)#*IP prefix-list tst permit 0.0.0.0/0 le 32*
> >>
> >>
> >>
> >> R2(config)#*router ospf 1*
> >>
> >> R2(config-router)#*area 1 filter-list prefix tst out*
> >>
> >>
> >>
> >> *To verify the configuration:*
> >>
> >> **
> >>
> >> *On R2*
> >>
> >>
> >>
> >> R2#*Show ip route ospf | I O*
> >>
> >> O IA 34.1.1.0 [110/65] via 23.1.1.3, 00:02:12, Serial0/0.23
> >>
> >> *O 1.1.1.0 [110/2] via 12.1.1.1, 00:02:12, FastEthernet0/0*
> >>
> >>
> >>
> >> R2#*Show ip ospf da router*
> >>
> >>
> >>
> >> *Link connected to: a Stub Network*
> >>
> >> * (Link ID) Network/subnet number: 1.1.1.0*
> >>
> >> * (Link Data) Network Mask: 255.255.255.0*
> >>
> >> * Number of TOS metrics: 0*
> >>
> >> * TOS 0 Metrics: 1*
> >>
> >>
> >>
> >> *The output of the above show command reveals that the area
> >> filter-list did not do anything to the routing table or the
> >> database of the router
> that
> >> it s configured on. But let s see how it affected the other
> >> routers:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3#*Show ip route ospf | I O*
> >>
> >> O IA 12.1.1.0 [110/65] via 23.1.1.2, 00:15:36, Serial0/0.32
> >>
> >>
> >>
> >> *GR8, it worked.*
> >>
> >> *So this may seem like both area range and the area filter-list
> >> commands do the same thing, because of the end result, b**ut let s
> >> configure the "Area Filter-list" on R3. Remember in the earlier
> >> test the area range command did not work on R3:*
> >>
> >> * *
> >>
> >> *Let s remove the previous command before testing it on R3:*
> >>
> >>
> >>
> >> *On R2*
> >>
> >> R2(config)#*router ospf 1*
> >>
> >> R2(config-router)#*No area 1 filter-list prefix tst out*
> >>
> >>
> >>
> >> *To verify the configuration:*
> >>
> >> **
> >>
> >> *On R3*
> >>
> >> R3#*Show ip route ospf | I O*
> >>
> >> *O IA 1.1.1.0 [110/66] via 23.1.1.2, 00:00:10, Serial0/0.32*
> >>
> >> O IA 12.1.1.0 [110/65] via 23.1.1.2, 00:17:47, Serial0/0.32
> >>
> >>
> >>
> >> *NOW .let s configure the area filter-list on R3:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3(config)#*ip prefix-list tst deny 1.1.1.0/24*
> >>
> >> R3(config)#*ip prefix-list tst permit 0.0.0.0/0 le 32*
> >>
> >>
> >>
> >> R3(config)#*router ospf 1*
> >>
> >> R3(config-router)#*area 0 filter-list prefix tst out*
> >>
> >>
> >>
> >> *Let s verify the routing table of R4*
> >>
> >>
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:29:01, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:19:23, FastEthernet0/0
> >>
> >>
> >>
> >> *So you can see that it did affect the routers in area 2. *
> >>
> >> *So the area range command can be used on the ABR that is
> >> directly connected to the area that originated the route
> >> (intra-area routes) or another way of saying it (Does NOT generate
> >> LSA-3 for the other areas), whereas, the Area filter-list command
> >> affects LSA type-3s and can be configured on any ABR within your
> >> routing domain.*
> >>
> >>
> >>
> >> *You could also use the following command to accomplish the same
> >> result, the following two methods will work on LSA Type-3s going
> >> from area 0 to another area: *
> >>
> >> **
> >>
> >> *Let s remove the previous command and verify:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3(config)#*router ospf 1*
> >>
> >> R3(config-router)#*No area 0 filter-list prefi tst out*
> >>
> >>
> >>
> >> *On R4*
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> *O IA 1.1.1.0 [110/67] via 34.1.1.3, 00:00:27, FastEthernet0/0*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:35:22, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:25:44, FastEthernet0/0
> >>
> >>
> >>
> >> *Let s configure a static route on R3 and point it to Null0:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3(config)#*IP route 1.1.1.0 255.255.255.0 null0*
> >>
> >>
> >>
> >> *To verify the configuration:*
> >>
> >> **
> >>
> >> *On R4*
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:37:00, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:27:22, FastEthernet0/0
> >>
> >>
> >>
> >> *Or the following: Let s remove the previous command and verify:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3(config)#*no IP route 1.1.1.0 255.255.255.0 null0*
> >>
> >>
> >>
> >> *On R4*
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> *O IA 1.1.1.0 [110/67] via 34.1.1.3, 00:00:27, FastEthernet0/0*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:37:54, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:28:16, FastEthernet0/0
> >>
> >>
> >>
> >> *Contrary to popular belief, the distribute-list in command can
> >> affect the neighboring router/s:*
> >>
> >>
> >>
> >> *On R3*
> >>
> >> R3(config)#*access-list 1 deny 1.1.1.0 0.0.0.255*
> >>
> >> R3(config)#*access-list 1 permit any*
> >>
> >>
> >>
> >> R3(config)#*router ospf 1*
> >>
> >> R3(config-router)#*distribute-list 1 in*
> >>
> >>
> >>
> >> *On R4*
> >>
> >> R4#*Show ip route ospf | I O*
> >>
> >> O IA 23.1.1.0 [110/65] via 34.1.1.3, 00:38:55, FastEthernet0/0
> >>
> >> O IA 12.1.1.0 [110/66] via 34.1.1.3, 00:29:17, FastEthernet0/0
> >>
> >>
> >>
> >> *I hope this helped.*
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> On Tue, Jan 1, 2013 at 9:36 PM, Sarad <tosara_at_gmail.com> wrote:
> >>
> >>> Hi All,
> >>>
> >>> May be it's not clear what I have sent before let me put this
> >>> straight,
> >>>
> >>> Other than direction (In/Out) what are the limitations of area
> >>> range command over filter-list command in term of OSPF LSA type 3 filtering?
> >>>
> >>> Thanks
> >>> Saranga
> >>>
> >>>
> >>> On Wed, Jan 2, 2013 at 4:16 PM, Sarad <tosara_at_gmail.com> wrote:
> >>>
> >>> > Hi Experts,
> >>> >
> >>> > Can somebody help me to get my head around this, I've been
> >>> > labbing
> ospf
> >>> > type 3 filtering, Main method use for this is filter-list command.
> >>> Which we
> >>> > can use to filter route based on the direction (in /out)
> >>> >
> >>> >
> >>> >
> >>> > Then there is area range command with not-advertise switch we
> >>> > can
> use to
> >>> > do limited filtering on ABR. When I tested this it only works
> >>> > when I
> >>> filter
> >>> > LSA type 3 from non backbone area to a backbone area.
> >>> >
> >>> > Can somebody help me to explain what is the exact usage of this
> command
> >>> in
> >>> > term of filtering in OSPF. There is nothing much in the doc CD
> >>> >
> >>> > *
> >>> > *
> >>> > *area area-id filter-list prefix prefix-list-name {in | out}
> >>> > area* area-id *range* ipv6-prefix /prefix-length [*advertise* |
> >>> > * not-advertise*] [*cost* cost]
> >>> >
> >>> >
> >>> > Cheers
> >>> > Sara
> >>>
> >>>
> >>> Blogs and organic groups at http://www.ccie.net
> >>>
> >>> __________________________________________________________________
> >>> _____ Subscription information may be found at:
> >>> http://www.groupstudy.com/list/CCIELab.html
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >> --
> >> *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
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > ____________________________________________________________________
> > ___ Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> >
> >
> >
> >
> >
>

--
*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
Blogs and organic groups at http://www.ccie.net