Network Setup for OSPF Type-4 LSA Generation – Scenario #1
Below shows that RT1 has originated a Type-5 External LSA when it becomes an ABSR by redistributing the static route to 10.0.0.0/8 using the redistribute static OSPF router subcommand.
RT1#sh ip ospf database external OSPF Router with ID (1.1.1.1) (Process ID 100) Type-5 AS External Link States LS age: 112 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x474B Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0 RT1#
Below shows that RT2 has received the Type-5 AS-External LSA from RT1.
It is propagating the Type-5 AS-External LSA to RT3 and originated a Type-4 ASBR-Summary LSA, as it is the ABR (between areas 0 and 1) that is resides within the same area as the ASBR – RT1.
RT2#sh ip ospf database asbr-summary OSPF Router with ID (2.2.2.2) (Process ID 100) Summary ASB Link States (Area 0) LS age: 51 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(AS Boundary Router) Link State ID: 1.1.1.1 (AS Boundary Router address) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x1B14 Length: 28 Network Mask: /0 TOS: 0 Metric: 1 RT2# RT2#sh ip ospf database external OSPF Router with ID (2.2.2.2) (Process ID 100) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 122 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x474B Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0 RT2#
RT3 has received the Type-5 AS-External LSA that is originated by RT1 and propagated by RT2, as well as the Type-4 ASBR-Summary LSA that is originated by RT2 for Area 0.
Note that it has originated another copy of Type-4 ASBR-Summary LSA into Area 2!
RT3#sh ip ospf database asbr-summary OSPF Router with ID (3.3.3.3) (Process ID 100) Summary ASB Link States (Area 0) Routing Bit Set on this LSA LS age: 55 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(AS Boundary Router) Link State ID: 1.1.1.1 (AS Boundary Router address) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x1B14 Length: 28 Network Mask: /0 TOS: 0 Metric: 1 Summary ASB Link States (Area 2) LS age: 40 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(AS Boundary Router) Link State ID: 1.1.1.1 (AS Boundary Router address) Advertising Router: 3.3.3.3 LS Seq Number: 80000001 Checksum: 0x723 Length: 28 Network Mask: /0 TOS: 0 Metric: 2 RT3# RT3#sh ip ospf database external OSPF Router with ID (3.3.3.3) (Process ID 100) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 125 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x474B Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0 RT3#
Below shows the Type-4 ASBR-Summary and Type-5 AS-External LSAs that are received upon RT4:
RT4#sh ip ospf database asbr-summary OSPF Router with ID (4.4.4.4) (Process ID 100) Summary ASB Link States (Area 2) Routing Bit Set on this LSA LS age: 44 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(AS Boundary Router) Link State ID: 1.1.1.1 (AS Boundary Router address) Advertising Router: 3.3.3.3 LS Seq Number: 80000001 Checksum: 0x723 Length: 28 Network Mask: /0 TOS: 0 Metric: 2 RT4# RT4#sh ip ospf database external OSPF Router with ID (4.4.4.4) (Process ID 100) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 129 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x474B Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0 RT4#
Network Setup for OSPF Type-4 LSA Generation – Scenario #2
Area 1 is an NSSA.
RT1 is originating a Type-7 NSSA-External LSA for 10.0.0.0/8.
RT2 converts the Type-7 NSSA-External LSA to Type-5 AS-External LSA before propagating it into other areas in the OSPF domain.
Below shows the configuration implemented on RT1 and RT2 to convert area 1 into an NSSA:
RT1#conf t Enter configuration commands, one per line. End with CNTL/Z. RT1(config)#router ospf 100 RT1(config-router)#area 1 nssa RT1(config-router)#end RT1# 00:04:36: %OSPF-5-ADJCHG: Process 100, Nbr 2.2.2.2 on FastEthernet1/0 from FULL to DOWN, Neighbor Down: Adjacency forced to reset 00:04:40: %OSPF-5-ADJCHG: Process 100, Nbr 2.2.2.2 on FastEthernet1/0 from LOADING to FULL, Loading Done RT1# ---------------------------------------------------------------------- RT2#conf t Enter configuration commands, one per line. End with CNTL/Z. RT2(config)#router ospf 100 RT2(config-router)#area 1 nssa RT2(config-router)#end RT2# 00:04:37: %OSPF-5-ADJCHG: Process 100, Nbr 1.1.1.1 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Adjacency forced to reset 00:04:39: %OSPF-5-ADJCHG: Process 100, Nbr 1.1.1.1 on FastEthernet0/0 from LOADING to FULL, Loading Done RT2#
Below shows that RT1 has originated a Type-7 NSSA-External LSA for 10.0.0.0/8, and RT2 has originated a Type-5 AS-External LSA for the Type-7 NSSA-External LSA:
RT1#sh ip ospf database nssa-external OSPF Router with ID (1.1.1.1) (Process ID 100) Type-7 AS External Link States (Area 1) LS age: 42 Options: (No TOS-capability, Type 7/5 translation, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x72F0 Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 12.12.12.1 External Route Tag: 0 RT1# ---------------------------------------------------------------------- RT2#sh ip ospf database external OSPF Router with ID (2.2.2.2) (Process ID 100) Type-5 AS External Link States LS age: 6 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xE880 Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 12.12.12.1 External Route Tag: 0 RT2# RT2#sh ip ospf database nssa-external OSPF Router with ID (2.2.2.2) (Process ID 100) Type-7 AS External Link States (Area 1) Routing Bit Set on this LSA LS age: 92 Options: (No TOS-capability, Type 7/5 translation, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x72F0 Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 12.12.12.1 External Route Tag: 0 RT2#
Below shows that RT3 has received the Type-5 AS-External LSA from RT2 and propagating it to RT4. It has originated a Type-4 ASBR-Summary LSA, as it is the ABR (between areas 0 and 2) that is resides within the same area as the ASBR – RT2.
RT3#sh ip ospf database asbr-summary OSPF Router with ID (3.3.3.3) (Process ID 100) Summary ASB Link States (Area 2) LS age: 26 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(AS Boundary Router) Link State ID: 2.2.2.2 (AS Boundary Router address) Advertising Router: 3.3.3.3 LS Seq Number: 80000001 Checksum: 0xCE58 Length: 28 Network Mask: /0 TOS: 0 Metric: 1 RT3# RT3#sh ip ospf database external OSPF Router with ID (3.3.3.3) (Process ID 100) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 11 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xE880 Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 12.12.12.1 External Route Tag: 0 RT3#
Finally, below shows the Type-4 ASBR-Summary and Type-5 AS-External LSAs that are received upon RT4:
RT4#sh ip ospf database asbr-summary OSPF Router with ID (4.4.4.4) (Process ID 100) Summary ASB Link States (Area 2) Routing Bit Set on this LSA LS age: 29 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(AS Boundary Router) Link State ID: 2.2.2.2 (AS Boundary Router address) Advertising Router: 3.3.3.3 LS Seq Number: 80000001 Checksum: 0xCE58 Length: 28 Network Mask: /0 TOS: 0 Metric: 1 RT4# RT4#sh ip ospf database external OSPF Router with ID (4.4.4.4) (Process ID 100) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 14 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.0.0.0 (External Network Number ) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xE880 Length: 36 Network Mask: /8 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 12.12.12.1 External Route Tag: 0 RT4#
I think you should notice here, that type 4 lsa is created because of the E bit settled in the flag field of type 1 lsa.
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