OSPF_LSA_Deep_Dive_Ver2

To lead off where we left, we made Area 15 an NSSA Area which stopped the Type 4 and 5 LSA’s from entering the Area, now we are going to do some Redistribution the other way and turn R5 in the NSSA Area into an ASBR.

I’ve created networks (loopbacks) 5.5.5.5 /32 and 55.5.5.0 /24, and will redistribute them into OSPF, again using the metric-type modifier as I believe the N1 and N2 routes function the same as E1 and E2 route types (though I could be wrong on that!):

R5#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R5(config)#router ospf 1
R5(config-router)#redistribute connected subnets metric-type 1
R5(config-router)#^Z
R5#

I will admit, again I did “sh ip route ospf” completely forgetting it will not show directly connected interfaces as an OSPF external route unless I give them an AD lower than 0.

However, let us take a look at the LS DB to see if anything has changed in there:

R5#sh ip ospf database

            OSPF Router with ID (5.5.5.5) (Process ID 1)

                Router Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Link count
5.5.5.5         5.5.5.5         161         0x8000000B 0x00B6AC 1
11.1.1.1        11.1.1.1        532         0x8000000C 0x00D39D 1

                Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.15.1     11.1.1.1        532         0x80000008 0x001D17

                Summary Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         11.1.1.1        532         0x80000007 0x008697
2.2.2.2         11.1.1.1        532         0x80000007 0x00DAFE
3.3.3.3         11.1.1.1        532         0x80000007 0x00AC29
11.1.1.1        11.1.1.1        532         0x80000007 0x000410
22.2.2.2        11.1.1.1        532         0x80000007 0x00D5EF
33.3.3.3        11.1.1.1        532         0x80000007 0x002592
172.12.34.0     11.1.1.1        532         0x80000007 0x006A9C
172.12.123.0    11.1.1.1        535         0x80000007 0x008925

                Type-7 AS External Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         5.5.5.5         164         0x80000001 0x0058C9 0
55.5.5.0        5.5.5.5         164         0x80000001 0x00FDF6 0
R5#

*Queue the Angels singing* JUST as expected, there are the networks under Link ID, the Advertising Routers RID, Age, …. some other stuff but then I see Tag in there.

Being the curious person I am, I will create a quick route map for the redistribute command and see if that populates in the LS DB:

R5(config)#
R5(config)#access-list 7 permit 5.5.5.5
R5(config)#access-list 7 permit 55.5.5.0 0.0.0.255
R5(config)#
R5(config)#route-map Tagging permit 10
R5(config-route-map)#match ip add 7
R5(config-route-map)#set tag 100
R5(config-route-map)#route-map Tagging permit 20
R5(config-route-map)#exit
R5(config)#
R5(config)#router ospf 1
R5(config-router)#no redistribute connected subnets metric-type 1
R5(config-router)#redistribute connected subnets metric-type 1 ?
metric     Metric for redistributed routes
route-map  Route map reference
tag        Set tag for routes redistributed into OSPF
<cr>

R5(config-router)#$e connected subnets metric-type 1 route-map Tagging
R5(config-router)#

I’ve never noticed in Route-Maps that you have a <cr> after match ip add, I am wondering if that is equivalent to the catch all “let other traffic flow normal” clause I put on sequence 20 by entering nothing. Hmm.

Anyways, lets see those tags in the LS DB! :

R5#sh ip ospf database

(Removed unnecessary output)

                Type-7 AS External Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         5.5.5.5         306         0x80000001 0x006756 100
55.5.5.0        5.5.5.5         306         0x80000001 0x000D83 100
R5#

Cool, so that is a very handy trick to know for exam day if you are asked to answer a tagging question, but “sh route” and “sh run” is disabled, you can run “sh ip ospf database” and see if Route-Maps are indeed tagging them and what they are tagging them with. Very good knowledge for exam day!

That knowledge aside, lets see how R1 is now seeing the network through it’s LS DB:

R1#sh ip ospf data

            OSPF Router with ID (11.1.1.1) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
11.1.1.1        11.1.1.1        1431        0x80000008 0x00D76C 2
22.2.2.2        22.2.2.2        453         0x80000008 0x008E8A 2
33.3.3.3        33.3.3.3        489         0x80000008 0x007E71 2

                Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.123.1    11.1.1.1        423         0x80000007 0x00A9EE

                Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         11.1.1.1        683         0x80000007 0x00E043
2.2.2.2         22.2.2.2        453         0x80000007 0x003AD7
3.3.3.3         33.3.3.3        489         0x80000007 0x00936C
172.12.15.0     11.1.1.1        423         0x80000009 0x00104E
172.12.34.0     33.3.3.3        489         0x80000007 0x0051DF

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
11.1.1.1        11.1.1.1        1431        0x80000007 0x00F018 1

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
2.2.2.2         11.1.1.1        423         0x80000007 0x0035AA
3.3.3.3         11.1.1.1        423         0x80000007 0x0007D4
11.1.1.1        11.1.1.1        683         0x80000007 0x005EBB
22.2.2.2        11.1.1.1        423         0x80000007 0x00309B
33.3.3.3        11.1.1.1        423         0x80000007 0x007F3E
172.12.15.0     11.1.1.1        423         0x80000009 0x00104E
172.12.34.0     11.1.1.1        423         0x80000007 0x00C448
172.12.123.0    11.1.1.1        683         0x80000007 0x00E3D0

                Summary ASB Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
22.2.2.2        11.1.1.1        423         0x80000007 0x0018B3

                Router Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Link count
5.5.5.5         5.5.5.5         1061        0x8000000B 0x00B6AC 1
11.1.1.1        11.1.1.1        1431        0x8000000C 0x00D39D 1

                Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.15.1     11.1.1.1        1431        0x80000008 0x001D17

                Summary Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         11.1.1.1        1431        0x80000007 0x008697
2.2.2.2         11.1.1.1        1431        0x80000007 0x00DAFE
3.3.3.3         11.1.1.1        1431        0x80000007 0x00AC29
11.1.1.1        11.1.1.1        1431        0x80000007 0x000410
22.2.2.2        11.1.1.1        1431        0x80000007 0x00D5EF
33.3.3.3        11.1.1.1        1431        0x80000007 0x002592
172.12.34.0     11.1.1.1        1431        0x80000007 0x006A9C
172.12.123.0    11.1.1.1        1431        0x80000007 0x008925

                Type-7 AS External Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         5.5.5.5         548         0x80000001 0x006756 100
55.5.5.0        5.5.5.5         548         0x80000001 0x000D83 100

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         11.1.1.1        547         0x80000001 0x001AB3 100
55.5.5.0        11.1.1.1        547         0x80000001 0x00BFE0 100
172.12.23.0     22.2.2.2        453         0x80000007 0x00141B 0
R1#

Wooooooah NELLY!!! That is a lot of output, but it perfectly demonstrates that Type 7 LSA’s (Routes Redistributed in NSSA’s) are defined by their network # in the LS DB but not ASBR’s outside of NSSA area – Another very good to know piece of information.

All sorts of good information as we piece LSA’s as a whole together!

So I am curious if R2 will not see the networks, as we know LSA Type 5’s will not enter an NSSA Area, will NSSA Redistributed routes not leave NSSA Areas? :

R2#sh ip route ospf
     1.0.0.0/32 is subnetted, 1 subnets
O IA    1.1.1.1 [110/65] via 172.12.123.1, 03:15:10, Serial0/0
     33.0.0.0/32 is subnetted, 1 subnets
O       33.3.3.3 [110/65] via 172.12.123.3, 03:15:10, Serial0/0
     3.0.0.0/32 is subnetted, 1 subnets
O IA    3.3.3.3 [110/65] via 172.12.123.3, 03:15:10, Serial0/0
     55.0.0.0/24 is subnetted, 1 subnets
O E1    55.5.5.0 [110/85] via 172.12.123.1, 00:14:34, Serial0/0
     5.0.0.0/32 is subnetted, 1 subnets
O E1    5.5.5.5 [110/85] via 172.12.123.1, 00:14:34, Serial0/0
     172.12.0.0/24 is subnetted, 4 subnets
O IA    172.12.34.0 [110/65] via 172.12.123.3, 03:15:10, Serial0/0
O IA    172.12.15.0 [110/65] via 172.12.123.1, 03:15:10, Serial0/0
     11.0.0.0/32 is subnetted, 1 subnets
O       11.1.1.1 [110/65] via 172.12.123.1, 03:15:10, Serial0/0
R2#

So an ASBR outside of an NSSA will create only Type 5 LSA’s that are not allowed inside the NSSA Area, however an ASBR inside the NSSA creates both Type 7 LSA’s for routers inside the NSSA Area, and also creates Type 5 LSA’s to be flooded outside of the NSSA.

^ That is the information you need to know to pass this beast of an exam. Moving on.

Next lets first look at R4’s current Route table, and then we will configure it as a Stub Area, as the ultimate goal is to keep routing tables complete and concise which this Area only has one way out so it’s the perfect candidate!

However, first we’ll start with a look at it’s current “sh ip route” and “sh ip ospf data” as we turn it first into a Stub Area, and then a Total Stub Area:

R4#sh ip ospf data

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum Link count
4.4.4.4         4.4.4.4         1019        0x80000005 0x000D45 1
33.3.3.3        33.3.3.3        1020        0x80000003 0x00BB64 1

                Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.34.3     33.3.3.3        1020        0x80000001 0x004DAA

                Summary Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         33.3.3.3        975         0x80000001 0x007E4F
2.2.2.2         33.3.3.3        855         0x80000001 0x005079
3.3.3.3         33.3.3.3        1059        0x80000001 0x009F66
11.1.1.1        33.3.3.3        975         0x80000001 0x00FBC7
22.2.2.2        33.3.3.3        855         0x80000001 0x004B6A
33.3.3.3        33.3.3.3        1059        0x80000001 0x0018CF
172.12.15.0     33.3.3.3        975         0x80000001 0x00B158
172.12.123.0    33.3.3.3        980         0x80000003 0x00FAA1

                Summary ASB Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
11.1.1.1        33.3.3.3        975         0x80000001 0x00E3DF
22.2.2.2        33.3.3.3        855         0x80000001 0x003382

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         11.1.1.1        965         0x80000001 0x001AB3 100
55.5.5.0        11.1.1.1        965         0x80000001 0x00BFE0 100
172.12.23.0     22.2.2.2        1007        0x80000001 0x002015 0
R4#
R4#
R4#sh ip route ospf

Gateway of last resort is not set

      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/66] via 172.12.34.3, 00:16:43, FastEthernet0/1
      2.0.0.0/32 is subnetted, 1 subnets
O IA     2.2.2.2 [110/66] via 172.12.34.3, 00:14:43, FastEthernet0/1
      3.0.0.0/32 is subnetted, 1 subnets
O IA     3.3.3.3 [110/2] via 172.12.34.3, 00:17:24, FastEthernet0/1
      5.0.0.0/32 is subnetted, 1 subnets
O E1     5.5.5.5 [110/86] via 172.12.34.3, 00:16:32, FastEthernet0/1
      11.0.0.0/32 is subnetted, 1 subnets
O IA     11.1.1.1 [110/66] via 172.12.34.3, 00:16:43, FastEthernet0/1
      22.0.0.0/32 is subnetted, 1 subnets
O IA     22.2.2.2 [110/66] via 172.12.34.3, 00:14:43, FastEthernet0/1
      33.0.0.0/32 is subnetted, 1 subnets
O IA     33.3.3.3 [110/2] via 172.12.34.3, 00:17:24, FastEthernet0/1
      55.0.0.0/24 is subnetted, 1 subnets
O E1     55.5.5.0 [110/86] via 172.12.34.3, 00:16:32, FastEthernet0/1
      172.12.0.0/16 is variably subnetted, 5 subnets, 2 masks
O IA     172.12.15.0/24 [110/66] via 172.12.34.3, 00:16:43, FastEthernet0/1
O E1     172.12.23.0/24 [110/85] via 172.12.34.3, 00:14:38, FastEthernet0/1
O IA     172.12.123.0/24 [110/65] via 172.12.34.3, 00:16:48, FastEthernet0/1
R4#

You should be able to read right down that list and say “This router has a Type 1, 2, 3, 4, and 5 LSA’s coming to it” at this point without thinking twice.

I wanted to show the route table as well, as that will shrink along with the Stubbing of this network, which the purpose of stubbing is really breaking it down to a single default route out of the network since it only has one path it can take – However we must know how it impacts the flow of LSA’s.

That being said, I hope the LSA Database is starting to burn into your memory, and lets make are 34 a Stub Area:

R4#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R4(config)#router ospf 1
R4(config-router)#area 34 stub
R4(config-router)#
*Apr 26 00:28:13.639: %OSPF-5-ADJCHG: Process 1, Nbr 33.3.3.3 on FastEthernet0/1 from FULL to DOWN, Neighbor Down: Adjacency forced to reset
R4(config-router)#
ASR#3
[Resuming connection 3 to r3 … ]

R3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#router ospf 1
R3(config-router)#area 34 stub
R3(config-router)#
*Mar 31 19:28:58.966: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.4 on FastEthernet0/1 from FULL to DOWN, Neighbor Down: Adjacency forced to reset
*Mar 31 19:28:59.174: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.4 on FastEthernet0/1 from LOADING to FULL, Loading Done
R3(config-router)#

As I mentioned, creating a Stub network will take the Adjacency down just as long as it takes you to configure both sides, along with NSSA Area configuration!

So let’s see what is happening on R4 now:

R4#sh ip ospf data

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum Link count
4.4.4.4         4.4.4.4         112         0x80000007 0x00272B 1
33.3.3.3        33.3.3.3        1673        0x80000003 0x00BB64 1

                Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.34.3     33.3.3.3        113         0x80000002 0x00698F

                Summary Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         33.3.3.3        113         0x80000001 0x0048CB
1.1.1.1         33.3.3.3        113         0x80000002 0x009A34
2.2.2.2         33.3.3.3        113         0x80000002 0x006C5E
3.3.3.3         33.3.3.3        113         0x80000002 0x00BB4B
11.1.1.1        33.3.3.3        113         0x80000002 0x0018AC
22.2.2.2        33.3.3.3        113         0x80000002 0x00674F
33.3.3.3        33.3.3.3        113         0x80000002 0x0034B4
172.12.15.0     33.3.3.3        113         0x80000002 0x00CD3D
172.12.123.0    33.3.3.3        113         0x80000004 0x001786
R4#

So we have lost our Type 4 and Type 5 LSA’s, but still have Types 1, 2, and 3 in the LS DB, and if you look carefully you can see it’s added a default route with the Advertising Router being R3 in our Type 3 LSA’s portion of the table “Summary Net Link States” (more on this soon). Lets look at the route table to see what exactly has happened there:

R4#sh ip route ospf

Gateway of last resort is 172.12.34.3 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 172.12.34.3, 00:04:18, FastEthernet0/1
      1.0.0.0/32 is subnetted, 1 subnets
O IA     1.1.1.1 [110/66] via 172.12.34.3, 00:04:18, FastEthernet0/1
      2.0.0.0/32 is subnetted, 1 subnets
O IA     2.2.2.2 [110/66] via 172.12.34.3, 00:04:18, FastEthernet0/1
      3.0.0.0/32 is subnetted, 1 subnets
O IA     3.3.3.3 [110/2] via 172.12.34.3, 00:04:18, FastEthernet0/1
      11.0.0.0/32 is subnetted, 1 subnets
O IA     11.1.1.1 [110/66] via 172.12.34.3, 00:04:18, FastEthernet0/1
      22.0.0.0/32 is subnetted, 1 subnets
O IA     22.2.2.2 [110/66] via 172.12.34.3, 00:04:18, FastEthernet0/1
      33.0.0.0/32 is subnetted, 1 subnets
O IA     33.3.3.3 [110/2] via 172.12.34.3, 00:04:18, FastEthernet0/1
      172.12.0.0/16 is variably subnetted, 4 subnets, 2 masks
O IA     172.12.15.0/24 [110/66] via 172.12.34.3, 00:04:18, FastEthernet0/1
O IA     172.12.123.0/24 [110/65] via 172.12.34.3, 00:04:18, FastEthernet0/1
R4#

So making the network a Stub Area has accomplished is stopping LSA Type 4’s and 5’s into the Area, so it won’t have External Routes from the Type 5’s as is doesn’t even know a path back to the ASBR provided by the Type 4 LSA, and it made a Default route to it’s only next hop out into the network.

So now we’ll take this that one step further, and make this Area a Total Stub, Stub Area:

R3(config-router)#no area 34 stub
*Mar 31 19:41:07.027: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.4 on FastEthernet0/1 from FULL to DOWN, Neighbor Down: Adjacency forced to reset
R3(config-router)#area 34 stub no-summary
R3(config-router)#
*Mar 31 19:41:20.341: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.4 on FastEthernet0/1 from DOWN to DOWN, Neighbor Down: Adjacency forced to reset
R3(config-router)#

It does only need to be issued on the edge router, but it can be issued on both, so lets see how the LS DB likes THAT on R4:

R4#sh ip ospf data

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum Link count
4.4.4.4         4.4.4.4         100         0x8000000A 0x00212E 1
33.3.3.3        33.3.3.3        101         0x80000006 0x00D34B 1

                Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.34.3     33.3.3.3        97          0x80000005 0x006392

                Summary Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         33.3.3.3        851         0x80000001 0x0048CB
R4#

Note the Type 3 LSA in the LS DB is the default route in the OSPF table, as seen here:

R4#sh ip route ospf

Gateway of last resort is 172.12.34.3 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 172.12.34.3, 00:03:01, FastEthernet0/1
R4#

Two points here, the default route has not changed from Stub to Total-Stub Stub Area as can be seen when comparing the two, and the only thing that making it a Total Stub was disallowing LSA Type 3 “Summary” LSA’s into the area (hence the command no-summary to make it a Total Stub) with one exception explained shortly.

So making an Area a Stub will Stop LSA 4 and 5 types from entering, and a Total Stub stops Type 3 LSA’s as well, leaving only Type 1’s and Type 2’s left inside of it.

Speaking of which, we can still gets Type 1’s and type 2’s inside of this area, lets try to make a couple of loopbacks to confirm this:

R4(config)#router ospf 1
R4(config-router)#network 4.4.4.4 0.0.0.0 area 34
R4(config-router)#^Z
R4#

I did a “sh ip route ospf” once again on R4 expecting to see it, and facepalmed as I did not see it there, and realized I was looking for a directly connected route in the ospf route table again – I think at this point I’m on the brink of mental exhaustion.

I actually was like “Where the diddly do is my route?” when it wasn’t there, and this is the phases of confirming the route is within the Area:

R4#sh ip route ospf

Gateway of last resort is 172.12.34.3 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 172.12.34.3, 00:24:47, FastEthernet0/1

What the diddly do!?!?!

R4#sh ip int bri
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            unassigned      YES NVRAM  administratively down down
FastEthernet0/1            172.12.34.4     YES NVRAM  up                    up
Loopback4                  4.4.4.4         YES NVRAM  up                    up

Yep the interface is configured as usual, is OSPF even seeing it??

R4#sh ip ospf data

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum Link count
4.4.4.4         4.4.4.4         267         0x8000000B 0x00022B 2
33.3.3.3        33.3.3.3        1537        0x80000006 0x00D34B 1

                Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.34.3     33.3.3.3        1533        0x80000005 0x006392

                Summary Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         33.3.3.3        2287        0x80000001 0x0048CB

Omg, I fell for the connected route thing again!!!

However it highlights one important aspect of all this LSA / Router Type brainwashing, and that is this real world or even lab world use for knowing the LS DB, I can verify that 4.4.4.4 is part of Area 34 even if I don’t see it on R4’s OSPF Specific route table – But I bet I can on R3! :

R3#sh ip route ospf
     1.0.0.0/32 is subnetted, 1 subnets
O IA    1.1.1.1 [110/65] via 172.12.123.1, 00:15:23, Serial0/2
     2.0.0.0/32 is subnetted, 1 subnets
O IA    2.2.2.2 [110/65] via 172.12.123.2, 00:15:23, Serial0/2
     4.0.0.0/32 is subnetted, 1 subnets
O       4.4.4.4 [110/2] via 172.12.34.4, 00:15:23, FastEthernet0/1
     55.0.0.0/24 is subnetted, 1 subnets
O E1    55.5.5.0 [110/85] via 172.12.123.1, 00:15:23, Serial0/2
     5.0.0.0/32 is subnetted, 1 subnets
O E1    5.5.5.5 [110/85] via 172.12.123.1, 00:15:23, Serial0/2
     172.12.0.0/24 is subnetted, 4 subnets
O IA    172.12.15.0 [110/65] via 172.12.123.1, 00:15:23, Serial0/2
     22.0.0.0/32 is subnetted, 1 subnets
O       22.2.2.2 [110/65] via 172.12.123.2, 00:36:45, Serial0/2
     11.0.0.0/32 is subnetted, 1 subnets
O       11.1.1.1 [110/65] via 172.12.123.1, 00:36:45, Serial0/2
R3#

In fact while on R3, let us gander upon its LS DB, because there are a few things to point out in it’s LS DB that are worth noting:

R3#sh ip ospf data

            OSPF Router with ID (33.3.3.3) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
11.1.1.1        11.1.1.1        787         0x80000004 0x00DF68 2
22.2.2.2        22.2.2.2        729         0x80000004 0x009686 2
33.3.3.3        33.3.3.3        708         0x80000004 0x00866D 2

                Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.123.1    11.1.1.1        531         0x80000004 0x00AFEB

                Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         11.1.1.1        1041        0x80000003 0x00E83F
2.2.2.2         22.2.2.2        729         0x80000003 0x0042D3
3.3.3.3         33.3.3.3        708         0x80000003 0x009B68
4.4.4.4         33.3.3.3        1150        0x80000001 0x007B85
172.12.15.0     11.1.1.1        787         0x80000007 0x00144C
172.12.34.0     33.3.3.3        449         0x80000002 0x005BDA

                Router Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum Link count
33.3.3.3        33.3.3.3        711         0x80000003 0x00E4E9 1

                Summary Net Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         33.3.3.3        711         0x80000003 0x007A51
2.2.2.2         33.3.3.3        711         0x80000003 0x004C7B
4.4.4.4         33.3.3.3        1153        0x80000001 0x007B85
11.1.1.1        33.3.3.3        711         0x80000003 0x00F7C9
22.2.2.2        33.3.3.3        711         0x80000003 0x00476C
33.3.3.3        33.3.3.3        711         0x80000003 0x0014D1
172.12.15.0     33.3.3.3        711         0x80000003 0x00AD5A
172.12.34.0     33.3.3.3        452         0x80000002 0x005BDA
172.12.123.0    33.3.3.3        711         0x80000005 0x00F6A3

                Summary ASB Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum
11.1.1.1        33.3.3.3        711         0x80000003 0x00DFE1
22.2.2.2        33.3.3.3        714         0x80000003 0x002F84

                Router Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum Link count
4.4.4.4         4.4.4.4         455         0x8000000C 0x00FF2C 2
33.3.3.3        33.3.3.3        454         0x80000007 0x00D14C 1

                Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.34.3     33.3.3.3        454         0x80000006 0x006193

                Summary Net Link States (Area 34)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         33.3.3.3        454         0x80000002 0x0046CC

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         11.1.1.1        792         0x80000003 0x0016B5 100
55.5.5.0        11.1.1.1        792         0x80000003 0x00BBE2 100
172.12.23.0     22.2.2.2        741         0x80000003 0x001C17 0
R3#

R3 is flooding Type 3 LSA’s into all other areas despite Area 34 being closed shut to incoming Type 3, 4, and 5 LSA’s, but also that R3 is actually flooding the default route in R4’s OSPF table is a Type 3 LSA, so this is something of a curiosity.

This Type 3 LSA default network was created by making a Stub Area which filters LSA Type 4 and 5’s from entering it, but when I made it a Total-Stub Stub Area, R3 is still flooding the single LSA Type 3 default route into Area 34.

So in as can be seen in the output the Area does allow the flooding of a Type 3 LSA for Total-Stub Stub’s, but only as a default route to its upstream Stub neighbor.

If on exam day I were asked “Do Total-Stub Stub Areas get Type 3 LSA’s injected into them?” there really is no black and white answer to that unless the question mentions something about R3’s default route Advertisement.

Food for thought.

Now onto the final looksy at LSA traffic before I face down on my keyboard, I want to demonstrate what happens in our NSSA when we make that an NSSA Total-Stub Area:

R1(config-router)#no area 15 nssa
R1(config-router)#area
*Apr 26 03:00:33.647: %OSPF-5-ADJCHG: Process 1, Nbr 55.5.5.5 on FastEthernet0/1 from FULL to DOWN, Neighbor Down: Adjacency forced to reset
R1(config-router)#area 15 nssa no-summary
R1(config-router)#
*Apr 26 03:00:50.031: %OSPF-5-ADJCHG: Process 1, Nbr 55.5.5.5 on FastEthernet0/1 from DOWN to DOWN, Neighbor Down: Adjacency forced to reset
*Apr 26 03:00:50.955: %OSPF-5-ADJCHG: Process 1, Nbr 55.5.5.5 on FastEthernet0/1 from LOADING to FULL, Loading Done
R1(config-router)#

So we’ve made this a “Total-Stub Not-So-Stubby-Area” which is clear as mud when you read it, right? So first lets take another look at R5’s “before” LS DB and OSPF route table:

R5#sh ip ospf database

            OSPF Router with ID (5.5.5.5) (Process ID 1)

                Router Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Link count
5.5.5.5         5.5.5.5         150         0x80000005 0x00BCAE 1
11.1.1.1        11.1.1.1        147         0x80000007 0x00DD98 1

                Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.15.1     11.1.1.1        147         0x80000003 0x002712

                Summary Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
1.1.1.1         11.1.1.1        152         0x80000002 0x009092
2.2.2.2         11.1.1.1        152         0x80000002 0x00E4F9
3.3.3.3         11.1.1.1        152         0x80000002 0x00B624
11.1.1.1        11.1.1.1        152         0x80000002 0x000E0B
22.2.2.2        11.1.1.1        152         0x80000002 0x00DFEA
33.3.3.3        11.1.1.1        152         0x80000002 0x002F8D
172.12.34.0     11.1.1.1        152         0x80000002 0x007497
172.12.123.0    11.1.1.1        160         0x80000002 0x009320

R5#sh ip route ospf
     1.0.0.0/32 is subnetted, 1 subnets
O IA    1.1.1.1 [110/2] via 172.12.15.1, 00:02:46, FastEthernet0/1
     2.0.0.0/32 is subnetted, 1 subnets
O IA    2.2.2.2 [110/66] via 172.12.15.1, 00:02:46, FastEthernet0/1
     33.0.0.0/32 is subnetted, 1 subnets
O IA    33.3.3.3 [110/66] via 172.12.15.1, 00:02:46, FastEthernet0/1
     3.0.0.0/32 is subnetted, 1 subnets
O IA    3.3.3.3 [110/66] via 172.12.15.1, 00:02:46, FastEthernet0/1
     172.12.0.0/24 is subnetted, 3 subnets
O IA    172.12.34.0 [110/66] via 172.12.15.1, 00:02:46, FastEthernet0/1
O IA    172.12.123.0 [110/65] via 172.12.15.1, 00:02:46, FastEthernet0/1
     22.0.0.0/32 is subnetted, 1 subnets
O IA    22.2.2.2 [110/66] via 172.12.15.1, 00:02:46, FastEthernet0/1
     11.0.0.0/32 is subnetted, 1 subnets
O IA    11.1.1.1 [110/2] via 172.12.15.1, 00:02:46, FastEthernet0/1
R5#

And after making the NSSA an NSSA Total-Stub:

R5#sh ip ospf data

            OSPF Router with ID (55.5.5.5) (Process ID 1)

                Router Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Link count
11.1.1.1        11.1.1.1        345         0x8000000D 0x00F972 1
55.5.5.5        55.5.5.5        934         0x80000006 0x009867 1

                Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.15.5     55.5.5.5        934         0x80000004 0x006267

                Summary Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         11.1.1.1        350         0x80000001 0x00C067

                Type-7 AS External Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         55.5.5.5        934         0x80000005 0x009BEB 100
55.5.5.0        55.5.5.5        934         0x80000005 0x004119 100
R5#

So by my quackulations, this will only contain the same type of default route R4 had in its routing table:

R5#sh ip route ospf
O*IA 0.0.0.0/0 [110/2] via 172.12.15.1, 00:08:57, FastEthernet0/1
R5#

So it turns out whether you add “… no-summary” to a Stub or NSSA network type, it will filter any Type 3 LSA’s, except the default route flooded into the Total-Stub network by its upstream Stub neighbor!

A quick look at R1’s new LS DB entries for Area 15 and its routes:

R5#sh ip ospf data

                Router Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Link count
11.1.1.1        11.1.1.1        903         0x8000000D 0x00F972 1
55.5.5.5        55.5.5.5        1493        0x80000006 0x009867 1

                Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
172.12.15.5     55.5.5.5        1493        0x80000004 0x006267

                Summary Net Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         11.1.1.1        908         0x80000001 0x00C067

                Type-7 AS External Link States (Area 15)

Link ID         ADV Router      Age         Seq#       Checksum Tag
5.5.5.5         55.5.5.5        1492        0x80000005 0x009BEB 100
55.5.5.0        55.5.5.5        1492        0x80000005 0x004119 100

Generating Type 1 LSA’s, reciving Type 2 LSA from the DR, as well as a Type 3 LSA with the default route from the Total-Stub configuration, and still generating Type 7 LSA’s from Redistributing connected routes.

One last look at R1’s “sh ip route ospf” :

R1# sh ip route ospf

Gateway of last resort is not set

      2.0.0.0/32 is subnetted, 1 subnets
O IA     2.2.2.2 [110/65] via 172.12.123.2, 00:16:31, Serial0/0/0
      3.0.0.0/32 is subnetted, 1 subnets
O IA     3.3.3.3 [110/65] via 172.12.123.3, 00:16:31, Serial0/0/0
      4.0.0.0/32 is subnetted, 1 subnets
O IA     4.4.4.4 [110/66] via 172.12.123.3, 00:16:31, Serial0/0/0
      5.0.0.0/32 is subnetted, 1 subnets
O N1     5.5.5.5 [110/21] via 172.12.15.5, 00:16:21, FastEthernet0/1
      22.0.0.0/32 is subnetted, 1 subnets
O        22.2.2.2 [110/65] via 172.12.123.2, 00:16:31, Serial0/0/0
      33.0.0.0/32 is subnetted, 1 subnets
O        33.3.3.3 [110/65] via 172.12.123.3, 00:16:31, Serial0/0/0
      55.0.0.0/24 is subnetted, 1 subnets
O N1     55.5.5.0 [110/21] via 172.12.15.5, 00:16:21, FastEthernet0/1
      172.12.0.0/16 is variably subnetted, 6 subnets, 2 masks
O E1     172.12.23.0/24 [110/84] via 172.12.123.2, 00:16:31, Serial0/0/0
O IA     172.12.34.0/24 [110/65] via 172.12.123.3, 00:16:31, Serial0/0/0
R1#

Note that it receives those routes as N1 routes, but any other router will see them as E1, and that about wraps up my deep dive into LSA and OSPF router types as I am going brain dead staring at the CLI (hurts so good).

You can extract some about the entire network from the local router with the Link State Database, so I really hope if you didn’t read it here, you read about it elsewhere as the topic of LSA’s across different network types is so broad its prime ground for exam questions for the ROUTE exam.

Not sure what is next yet, but I will stop rambling about LSA’s now, and move onto another DEEP dive before exam day!

I am now officially fried, and doing something other than studying now 🙂