OSPF Stub Area Types
Share this page:First lets make sure we’re comfortable with the LSA types, because you will not understand Stubs before you understand LSAs 100%
*LSA - Link State Advertisement, Each LSA has a LSID (Link State ID, like Router-ID for the LSAs)
LSA 1 - Router LSA, One per Router (Generated by Each Router)
LSA 2 - Network LSA, One per Network (Generated by DR)
LSA 3 - Summary LSA, One per Area (generated by ABR when LSAs 1 and 2 are injected into another Area). LSA3 = Subnet + Mask + Cost to reach the Network
LSA 4 - Summary External LSA, One per Autonomous System (Generated by ASBR)
LSA 5 - External LSA, Injected into OSPF from another routing process (non-ospf)
LSA 6 - Grout Membership LSA, Not supported by Cisco
LSA 7 - NSSA External, Generated by ASBR inside the NSSA instead of LSA 5 (details explained below, NSSA Section)
LSA 8-11 - Not implemented by Cisco
Check the LSA Statistics using the command:
Cisqueros_R3(config-router)#do show ip ospf stat
** OSPF Router with ID (3.3.3.3) (Process ID 1)**
** Area 0: SPF algorithm executed 4 times**
** Summary OSPF SPF statistic**
** SPF calculation time**
**Delta T Intra D-Intra Summ D-Summ Ext D-Ext Total Reason**
**00:22:26 0 0 0 0 0 0 0 R**
**00:22:16 0 0 0 0 0 0 0 R**
**00:21:47 0 0 0 0 0 0 0 R, N, SN**
**00:20:01 0 0 0 0 0 0 0 R, SN**
Check the OSPF DATABASE and all the LSAs currently in it:
Cisqueros_R3#show ip ospf database **
** OSPF Router with ID (3.3.3.3) (Process ID 1)
** Router Link States (Area 0) <— LSA1**
**Link ID ADV Router Age Seq# Checksum Link count**
**2.2.2.2 2.2.2.2 79 0x80000003 0x000E94 2**
**3.3.3.3 3.3.3.3 78 0x80000007 0x006F2C 4**
**4.4.4.4 4.4.4.4 52 0x80000004 0x007781 3**
** Net Link States (Area 0) ****<— LSA2**
**Link ID ADV Router Age Seq# Checksum**
**10.1.23.3 3.3.3.3 78 0x80000001 0x00658F**
** Summary Net Link States (Area 0) ****<— LSA3**
**Link ID ADV Router Age Seq# Checksum**
**1.1.1.0 2.2.2.2 124 0x80000002 0x00B33C**
**2.2.2.0 2.2.2.2 124 0x80000002 0x000D20**
**10.1.12.0 2.2.2.2 124 0x80000002 0x00BA22**
**10.1.45.0 4.4.4.4 43 0x80000001 0x00F5F4**
**44.4.4.0 4.4.4.4 43 0x80000001 0x008077**
** Router Link States (Area 1) **<— LSA1, Area 1
Link ID ADV Router Age Seq# Checksum Link count
3.3.3.3 3.3.3.3 89 0x80000007 0x00AC78 0
** Router Link States (Area 2) **<— LSA2, Area 1
Link ID ADV Router Age Seq# Checksum Link count
3.3.3.3 3.3.3.3 90 0x80000006 0x00AE77 0
STUB - No LSA 5 (E1 and E2) advertised on ABRs. You cannot use a Virtual Link here, but GRE Tunnel is an option.
Totally Stubby Area - Stub without the Summary Routes (LSA3), so no Intra-Area (IA O). Only Route and Network LSAs (LSA1 and LSA2) within the Area
The “no-summary” attribute is ONLY necessary on ABR, because the ABR is the only router that actually originates the LSA 3.
* STUB and Totally Stubby Area: DO NOT FORGET to configure the “area X stub” on all the routers in the Area X. The routers that ONLY belong to the Area X will BY DEFAULT get the Default Route injected with the ABR as a Default Gateway.
NSSA - LSA3 and LSA7 copied into LSA5 (External, E1 and E2)
* ASBR Generates LSA 7 instead of LSA 5 because the LSA 5 is not supported by NSSA. Then the ABR transforms it into LSA 5 on the ingress from NSSA to the regular OSPF Area.
Totally Stubby NSSA - No Summary (LSA3), but External Routes Included (LSA5)