Hi Paul,
Yes, as you know, Type 2 LSAs contains the mask of the segment to the DR. You are correct that it is part of the reachability information. How are they related to "area range" or "area filter-list" though?
Brian McGahan, CCIE #8593 (R&S/SP/Security)
bmcgahan_at_INE.com<mailto:bmcgahan_at_INE.com>
Internetwork Expert, Inc.
http://www.INE.com
On Jan 3, 2013, at 12:34 AM, "Paul Negron" <negron.paul_at_gmail.com<mailto:negron.paul_at_gmail.com>> wrote:
I would take that a step further.
If the Type 2 only describes the topology, then how does the router know what the mask of the ethernet link is?
The only place I see it is in the Type 2 LSA.
In fact, the Router LSA does not even increment the link count when the ethernet link is flapped and brought back up.
Paul Negron
CCIE# 14856
negron.paul_at_gmail.com<mailto:negron.paul_at_gmail.com>
303-725-8162
On Jan 2, 2013, at 8:54 PM, Narbik Kocharians <narbikk_at_gmail.com<mailto:narbikk_at_gmail.com>> wrote:
I meant to say No theory, show it in IOS.
On Wed, Jan 2, 2013 at 7:53 PM, Narbik Kocharians <narbikk_at_gmail.com<mailto:narbikk_at_gmail.com>> wrote:
Can you show me what LSA conveys the Ethernet link between R1 and R2? In
my example. Once again no theory IOS.
On Wed, Jan 2, 2013 at 7:48 PM, Joseph L. Brunner <joe_at_affirmedsystems.com<mailto:joe_at_affirmedsystems.com>
wrote:
Clap Clap Clap Clap ((|))((|))
=X=
UUU UUU
MEOWTH!!!
That was the best post in 6 years here....
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@groupstudy.com<mailto:nobody@groupstudy.com> [mailto:nobody@groupstudy.com<http://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<mailto: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<mailto: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<mailto: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<mailto:bmcgahan_at_ine.com>> wrote:
How does it affect Type 2 LSAs?
Brian McGahan, CCIE #8593 (R&S/SP/Security) bmcgahan_at_INE.com<mailto:bmcgahan_at_INE.com>
Internetwork Expert, Inc.
http://www.INE.com
-----Original Message-----
From: nobody_at_groupstudy.com<mailto: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<mailto: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<mailto: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<mailto: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<mailto: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<mailto: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
Received on Thu Jan 03 2013 - 01:21:48 ART
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