LSA types

1. Router LSA – This LSA is produced by every router. The LSA contains information of the router’s connected interfaces, states, neighbour router type, any known ospf routers connected to the router’s link and outgoing cost of each link. This LSA floods within its own area (intra-area flooding), hence this LSA describes intra-area route.


r1#show ip ospf database router

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

LS age: 265
 Options: (No TOS-capability, DC)
 LS Type: Router Links
 Link State ID: 1.1.1.1
 Advertising Router: 1.1.1.1
 LS Seq Number: 80000008
 Checksum: 0xE690
 Length: 48
 Number of Links: 2

Link connected to: a Stub Network
 (Link ID) Network/subnet number: 1.1.1.1
 (Link Data) Network Mask: 255.255.255.255
 Number of TOS metrics: 0
 TOS 0 Metrics: 1

Link connected to: a Transit Network
 (Link ID) Designated Router address: 172.30.0.1
 (Link Data) Router Interface address: 172.30.0.1
 Number of TOS metrics: 0
 TOS 0 Metrics: 1


 Routing Bit Set on this LSA
 LS age: 1867
 Options: (No TOS-capability, DC)
 LS Type: Router Links
 Link State ID: 2.2.2.2
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000008
 Checksum: 0xD98F
 Length: 48
 Area Border Router
 Number of Links: 2

Link connected to: a Stub Network
 (Link ID) Network/subnet number: 2.2.2.2
 (Link Data) Network Mask: 255.255.255.255
 Number of TOS metrics: 0
 TOS 0 Metrics: 1

Link connected to: a Transit Network
 (Link ID) Designated Router address: 172.30.0.1
 (Link Data) Router Interface address: 172.30.0.2
 Number of TOS metrics: 0
 TOS 0 Metrics: 1


 Routing Bit Set on this LSA
 LS age: 1897
 Options: (No TOS-capability, DC)
 LS Type: Router Links
 Link State ID: 3.3.3.3
 Advertising Router: 3.3.3.3
 LS Seq Number: 80000007
 Checksum: 0xCB91
 Length: 48
 Area Border Router
 Number of Links: 2

Link connected to: a Stub Network
 (Link ID) Network/subnet number: 3.3.3.3
 (Link Data) Network Mask: 255.255.255.255
 Number of TOS metrics: 0
 TOS 0 Metrics: 1

Link connected to: a Transit Network
 (Link ID) Designated Router address: 172.30.0.1
 (Link Data) Router Interface address: 172.30.0.3
 Number of TOS metrics: 0
 TOS 0 Metrics: 1


r1#

2. Network LSA – Produced by every DR in multi-access network. Network LSA floods within its own area. Describes all connected OSPF routers including the DR itself. The DR represents all connected router within its own area as a pesudonode, hence a network LSA represents a pseudonode just as a router LSA represents as a single physical router.


r1#show ip ospf database network

OSPF Router with ID (1.1.1.1) (Process ID 1)

Net Link States (Area 0)

Routing Bit Set on this LSA
 LS age: 416
 Options: (No TOS-capability, DC)
 LS Type: Network Links
 Link State ID: 172.30.0.1 (address of Designated Router)
 Advertising Router: 1.1.1.1
 LS Seq Number: 80000007
 Checksum: 0x92B5
 Length: 36
 Network Mask: /24
 Attached Router: 1.1.1.1
 Attached Router: 2.2.2.2
 Attached Router: 3.3.3.3

r1#

3. Network Summary LSA – Produced by ABR. This LSA advertises routes outside the area, for instance R2 is the ABR of area 0 and 10. R2 advertises route to area 10 within area 0, R2 also advertises route to area 0 within area 10. Default routes external to the area, but internal to the OSPF autonomous system are also advertised by network summary LSA.


r2#show ip ospf database summary

OSPF Router with ID (2.2.2.2) (Process ID 1)

Summary Net Link States (Area 0)

Routing Bit Set on this LSA
 LS age: 1846
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 4.4.4.4 (summary Network Number)
 Advertising Router: 3.3.3.3
 LS Seq Number: 80000007
 Checksum: 0x4C05
 Length: 28
 Network Mask: /32
 TOS: 0 Metric: 201

LS age: 793
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 5.5.5.5 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000006
 Checksum: 0x3E14
 Length: 28
 Network Mask: /32
 TOS: 0 Metric: 201

LS age: 1817
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 172.30.10.0 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0x7C15
 Length: 28
 Network Mask: /24
 TOS: 0 Metric: 200

Routing Bit Set on this LSA
 LS age: 1850
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 172.30.20.0 (summary Network Number)
 Advertising Router: 3.3.3.3
 LS Seq Number: 80000007
 Checksum: 0xEF93
 Length: 28
 Network Mask: /24
 TOS: 0 Metric: 200


 Summary Net Link States (Area 10)

LS age: 1823
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 1.1.1.1 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0x2702
 Length: 28
 Network Mask: /32
 TOS: 0 Metric: 2

LS age: 1825
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 2.2.2.2 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0xEE37
 Length: 28
 Network Mask: /32
 TOS: 0 Metric: 1

LS age: 1827
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 3.3.3.3 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0xCA56
 Length: 28
 Network Mask: /32
 TOS: 0 Metric: 2

LS age: 1828
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 4.4.4.4 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0x74DF
 Length: 28
 Network Mask: /32
 TOS: 0 Metric: 202

LS age: 1829
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 172.30.0.0 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0x1D46
 Length: 28
 Network Mask: /24
 TOS: 0 Metric: 1

LS age: 1831
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(Network)
 Link State ID: 172.30.20.0 (summary Network Number)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000007
 Checksum: 0x186E
 Length: 28
 Network Mask: /24
 TOS: 0 Metric: 201

r2#

4. ASBR summary LSA – Produced by ABR. This LSA is identical to type 3 network summary LSA except it only advertises the destination of ASBR. This LSA describes which router is doing redistribution. This LSA floods inter-area.


r2#show ip ospf database asbr-summary

OSPF Router with ID (2.2.2.2) (Process ID 1)

Summary ASB Link States (Area 0)

LS age: 1121
 Options: (No TOS-capability, DC, Upward)
 LS Type: Summary Links(AS Boundary Router)
 Link State ID: 5.5.5.5 (AS Boundary Router address)
 Advertising Router: 2.2.2.2
 LS Seq Number: 80000001
 Checksum: 0x3027
 Length: 28
 Network Mask: /0
 TOS: 0 Metric: 200

r2#

As shown above, the destination of ASBR is revealed in type 4 ASBR summary LSA.

5. Autonomous System External LSA – Produced by ASBR. This LSA either advertises a destination external to OSPF autonomous system or a default route external to the OSPF autonomous system. In essence it advertises redistributed routes. This is the only LSA that is not associated with any area or area types.


r5#show ip ospf database external

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

Type-5 AS External Link States

LS age: 1605
 Options: (No TOS-capability, DC)
 LS Type: AS External Link
 Link State ID: 192.168.0.0 (External Network Number )
 Advertising Router: 5.5.5.5
 LS Seq Number: 80000001
 Checksum: 0xAB61
 Length: 36
 Network Mask: /30
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 200
 Forward Address: 0.0.0.0
 External Route Tag: 100

r5#

6. MOSPF – Not supported by Cisco router. If MOSPF is received by Cisco router syslog message will be generated.


r5(config)#router ospf 1
r5(config-router)#ignore lsa mospf
r5(config-router)#

Ignoring mospf LSA will prevent syslog messages from being produced if mospf lsa is received.

7. NSSA LSA – Produced by ASBR of Not-so-stubby-Area type. This LSA is only flooded within NSSA, it describes redistributed routes within NSSA only. OSPF routers within NSSA must be NSSA type otherwise no adjacency can be formed.

show ip ospf database nssa-external
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