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Figure 1 - Network Scenario |
We made a bit of changes to our network scenario, follow the changes and proceed ahead to the configurations for the NSSA area.
This could get probably really confusing but to prevent that let’s just make a review on what kind of areas we could define in an ospf network.
Normal areas: normal ospf areas which have no limitations, all advertised routes are accepted in this type of area.
Stub areas: no type 5 autonomous system LSA’s are allowed to be advertised in this area, we’re also not allowed to have ASBR’s defined in this area.
Totally Stub area: additional to type 5 LSA’s (not allowed in stub areas), type 3 (ABR Summary LSA’s) and type 4 LSA’s (ASBR summary LSA’s) are not allowed to propagate into this area.
Not So Stubby area (NSSA): no type 5 LSA’s (ASBR external LSA’s) are allowed but type 7 LSA’s (NSSA external LSA’s) are allowed to be translated into type 5 (ABR external LSA’s) and traverse the ABR router.
Totally Not So Stubby area (TNSSA): no type 5 LSA’s (ASBR external LSA’s), no type 3 (ABR Summary LSA’s) and finally no type 4 LSA’s (ASBR summary LSA’s) are allowed to propagate into this area but type 7 LSA’s (NSSA external LSA’s) are allowed to be translated into type 5 (ABR external LSA’s) and traverse the ABR router.
From where we configured stub areas we were not able to have any autonomous system border router included to our stub areas and we were also not able to advertise ASBR external LSA’s into the stub area, to overcome these limitations the not so stubby area was introduced in the RFC 1587 so that we could have kept the specifications of a stub area while we could have inserted the type 5 LSA’s we needed into the area in a limited fashion. In this case we are still not able to redistribute type 5 external routes but instead the NSSA ASBR would create a new generation of LSA’s called type 7 LSA’s where after on at the NSSA-ABR (R2) these routes would be translated back to type 5 LSA’s and would be redistributed into the OSPF network in the 0.0.0.0 area.
In this chapter we would only be configuring the TNSSA area, the NSSA is just simply the same with the difference that the summary LSA’s show up in the ospf database but in the case of TNSSA the default route of 0.0.0.0 would be replaced instead of all the summary type 3 and type 4 LSA’s.
To get a better view the following ospf databases would show the change before the configurations and after we configure the 1.1.1.1 as a NSSA area.
Let’s take a look at R1, R2 and also R5 ospf databases.
vyatta@r1:~$ show ip ospf database
OSPF Router with ID (127.1.1.1)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Link count
127.1.1.1 127.1.1.1 1377 0x80000003 0x1a4c 2
127.2.2.2 127.2.2.2 1374 0x80000003 0xf466 2
127.3.3.3 127.3.3.3 1376 0x80000004 0xee62 2
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
10.10.10.3 127.3.3.3 1376 0x80000002 0xb763
Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Route
50.50.50.0 127.2.2.2 448 0x80000001 0x1b1c 50.50.50.0/24
127.5.5.5 127.2.2.2 433 0x80000001 0x6fc5 127.5.5.5/32
ASBR-Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
127.5.5.5 127.2.2.2 433 0x80000001 0xfc41
AS External Link States
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.5.5.5 242 0x80000001 0xf3ff E2 20.20.20.0/24 [0x0]
60.60.60.0 20.20.20.5 1376 0x80000002 0x3196 E2 60.60.60.0/24 [0x0]
60.60.60.0 127.5.5.5 445 0x80000001 0x4e2d E2 60.60.60.0/24 [0x0]
In our ospf database on R1 we have AS external link states already generated by the ASBR (R5), since R5 is our autonomous system border router and since we already have configured R5 to redistribute connected and also RIP routes it would be advertising these type of LSA’s into our 0.0.0.0 area, later on after we configure 1.1.1.1 as the TNSSA area these link states would be advertised by R2, in better words the external routes injected into the 1.1.1.1 by R5 would be translated into type 5 LSA’s by the TNSSA area border router.
Let’s take a look at R2:
vyatta@r2:~$ show ip ospf database
OSPF Router with ID (127.2.2.2)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Link count
127.1.1.1 127.1.1.1 1424 0x80000003 0x1a4c 2
127.2.2.2 127.2.2.2 1420 0x80000003 0xf466 2
127.3.3.3 127.3.3.3 1423 0x80000004 0xee62 2
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
10.10.10.3 127.3.3.3 1423 0x80000002 0xb763
Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Route
50.50.50.0 127.2.2.2 494 0x80000001 0x1b1c 50.50.50.0/24
127.5.5.5 127.2.2.2 479 0x80000001 0x6fc5 127.5.5.5/32
ASBR-Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
127.5.5.5 127.2.2.2 479 0x80000001 0xfc41
Router Link States (Area 1.1.1.1)
Link ID ADV Router Age Seq# CkSum Link count
127.2.2.2 127.2.2.2 488 0x80000006 0x1aea 1
127.5.5.5 127.5.5.5 489 0x80000003 0xd573 2
Net Link States (Area 1.1.1.1)
Link ID ADV Router Age Seq# CkSum
50.50.50.5 127.5.5.5 490 0x80000001 0x4ccf
Summary Link States (Area 1.1.1.1)
Link ID ADV Router Age Seq# CkSum Route
10.10.10.0 127.2.2.2 208 0x80000002 0xbeef 10.10.10.0/24
127.1.1.1 127.2.2.2 1420 0x80000001 0xf34d 127.1.1.1/32
127.3.3.3 127.2.2.2 1420 0x80000001 0xb189 127.3.3.3/32
AS External Link States
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.5.5.5 287 0x80000001 0xf3ff E2 20.20.20.0/24 [0x0]
60.60.60.0 20.20.20.5 1422 0x80000002 0x3196 E2 60.60.60.0/24 [0x0]
60.60.60.0 127.5.5.5 490 0x80000001 0x4e2d E2 60.60.60.0/24 [0x0]
Since we yet haven’t configured the area 1.1.1.1 as a TNSSA area we still have summary link states in our R2 ospf database, and as we mentioned before the AS external routes are advertised by R5.
Let’s take a look at R5 (same description goes for R5 as well):
vyatta@v5:~$ show ip ospf database
OSPF Router with ID (127.5.5.5)
Router Link States (Area 1.1.1.1)
Link ID ADV Router Age Seq# CkSum Link count
127.2.2.2 127.2.2.2 576 0x80000006 0x1aea 1
127.5.5.5 127.5.5.5 576 0x80000003 0xd573 2
Net Link States (Area 1.1.1.1)
Link ID ADV Router Age Seq# CkSum
50.50.50.5 127.5.5.5 576 0x80000001 0x4ccf
Summary Link States (Area 1.1.1.1)
Link ID ADV Router Age Seq# CkSum Route
10.10.10.0 127.2.2.2 296 0x80000002 0xbeef 10.10.10.0/24
127.1.1.1 127.2.2.2 6 0x80000002 0xf14e 127.1.1.1/32
127.3.3.3 127.2.2.2 1508 0x80000001 0xb189 127.3.3.3/32
AS External Link States
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.5.5.5 374 0x80000001 0xf3ff E2 20.20.20.0/24 [0x0]
60.60.60.0 20.20.20.5 1509 0x80000002 0x3196 E2 60.60.60.0/24 [0x0]
60.60.60.0 127.5.5.5 576 0x80000001 0x4e2d E2 60.60.60.0/24 [0x0]
Let’s make the configurations and see the changes:
vyatta@v5# configure
vyatta@v5# set protocols ospf area 1.1.1.1 area-type nssa no-summary
vyatta@v5# commit
vyatta@r2# configure
vyatta@r2# set protocols ospf area 1.1.1.1 area-type nssa no-summary
vyatta@r2# commit
Let’s see the changes (if your ospf database doesn’t read what’s written below be patient there are possibly some routes which would age out after an hour 3600s):
vyatta@r2:~$ show ip ospf database
OSPF Router with ID (127.2.2.2)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Link count
127.1.1.1 127.1.1.1 1180 0x80000005 0x164e 2
127.2.2.2 127.2.2.2 1277 0x80000005 0xf660 2
127.3.3.3 127.3.3.3 1180 0x80000006 0xea64 2
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
10.10.10.3 127.3.3.3 1180 0x80000004 0xb365
Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Route
50.50.50.0 127.2.2.2 1484 0x80000002 0x191d 50.50.50.0/24
127.5.5.5 127.2.2.2 172 0x80000003 0x6bc7 127.5.5.5/32
ASBR-Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
127.5.5.5 127.2.2.2 1033 0x80000002 0xfa42
Router Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum Link count
127.2.2.2 127.2.2.2 1275 0x8000000a 0xbd3b 1
127.5.5.5 127.5.5.5 1276 0x80000007 0x73cb 2
Net Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum
50.50.50.5 127.5.5.5 1281 0x80000002 0xef25
Summary Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum Route
0.0.0.0 127.2.2.2 833 0x80000002 0xebeb 0.0.0.0/0
NSSA-external Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.5.5.5 1274 0x80000003 0x99bf E2 20.20.20.0/24 [0x0]
60.60.60.0 127.5.5.5 1114 0x80000004 0xf1ed E2 60.60.60.0/24 [0x0]
AS External Link States
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.2.2.2 1273 0x80000003 0x6dfe E2 20.20.20.0/24 [0x0]
60.60.60.0 127.2.2.2 1113 0x80000004 0xc52d E2 60.60.60.0/24 [0x0]
On R2 the summary link states have been removed and instead a default route of 0.0.0.0 has been replaced (we expected this to happen since in a totally not so stubby area ospf summary link states are replaced by the default route – using the no summary parameter excludes these routes), we also have generated new NSSA-external link stated which are normally generated by the ASBR (R5), and we also have generated two similar routes to what we had in the previous entries of our database but with a little difference where they are advertised by the TNSSA border router (R2), as we stated, the link states injected by the ASBR into the 1.1.1.1 area once they get to the TNSSA ABR are translated back to type 5 LSA’s and are advertised to the 0.0.0.0 backbone area.
Let’s take a look at R1:
vyatta@r1:~$ show ip ospf database
OSPF Router with ID (127.1.1.1)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Link count
127.1.1.1 127.1.1.1 1276 0x80000005 0x164e 2
127.2.2.2 127.2.2.2 1375 0x80000005 0xf660 2
127.3.3.3 127.3.3.3 1276 0x80000006 0xea64 2
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
10.10.10.3 127.3.3.3 1276 0x80000004 0xb365
Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Route
50.50.50.0 127.2.2.2 1581 0x80000002 0x191d 50.50.50.0/24
127.5.5.5 127.2.2.2 270 0x80000003 0x6bc7 127.5.5.5/32
ASBR-Summary Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
127.5.5.5 127.2.2.2 1130 0x80000002 0xfa42
AS External Link States
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.2.2.2 1371 0x80000003 0x6dfe E2 20.20.20.0/24 [0x0]
60.60.60.0 127.2.2.2 1211 0x80000004 0xc52d E2 60.60.60.0/24 [0x0]
As you see on R1 we no longer have our AS external link states generated by the R5 ASBR router instead they are advertised as type 5 LSA’s while translated from type 7 LSA’s into the 0.0.0.0 area (these LSA’s are self originated by the ABR router, in order to view the self originated routes by the router run the show ip ospf database command with the self originate parameter) .
Let’s take a look at R5:
vyatta@v5:~$ show ip ospf database
OSPF Router with ID (127.5.5.5)
Router Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum Link count
127.2.2.2 127.2.2.2 461 0x8000000c 0x9b5e 1
127.5.5.5 127.5.5.5 450 0x80000008 0x2f12 2
Net Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum
50.50.50.2 127.2.2.2 461 0x80000001 0x4fd2
Summary Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum Route
0.0.0.0 127.2.2.2 1711 0x80000002 0xebeb 0.0.0.0/0
NSSA-external Link States (Area 1.1.1.1 [NSSA])
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 127.5.5.5 455 0x80000005 0x95c1 E2 20.20.20.0/24 [0x0]
60.60.60.0 127.5.5.5 455 0x80000006 0xedef E2 60.60.60.0/24 [0x0]
AS External Link States
Link ID ADV Router Age Seq# CkSum Route
20.20.20.0 20.20.20.5 3600 0x80000001 0xd868 E2 20.20.20.0/24 [0x0]
20.20.20.0 127.5.5.5 455 0x80000005 0xeb04 E2 20.20.20.0/24 [0x0]
60.60.60.0 127.5.5.5 455 0x80000006 0x4432 E2 60.60.60.0/24 [0x0]
On R5 we have both type 5 and also type 7 LSA’s the type 5 LSA’s are self originated by the router itself (shown as AS-external Link States) but are injected as type 7 LSA’s into the 1.1.1.1 TNSSA area (these routes are self originated and advertised in the 1.1.1.1 area).
What we just configured was a totally not so stubby area, since we added the no-summary option to the NSSA area, the summary routes area replaced by the 0.0.0.0 default route and the area is considered to be a totally not so stubby area, to regenerate the summary type 3 and type 4 link states remove the no-summary parameter and only configure the area as a NSSA area.
You could also manage the translation process by using the following commands:
vyatta@v5# set protocols ospf area 1.1.1.1 area-type nssa translate
possible completions:
always Configure NSSA-ABR to always translate
candidate Configure NSSA-ABR for translate election (default)
never Configure NSSA-ABR to never translate
CONTINUE TO PART 9 - VIRTUAL LINKS |
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