Demystifying the OSPFv3 database – Part 2

In yesterday’s post I forgot to mention a very interesting behaviour of the way router’s originate Type9 LSAs over a broadcast segment. Let’s remind ourselves of the topology we were up to:
OSPFv3-3
I’ve reset this topology and currently R3 is the DR. Let’s first check the non-broadcast link between R1 and R2. Each router oritiginates a Type9 with all their OSPFv3 enabled prefixes. This includes the link between them:

R2#show ospfv3 database prefix self-originate

          OSPFv3 1 address-family ipv6 (router-id 2.2.2.2)

		Intra Area Prefix Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 568
  LS Type: Intra-Area-Prefix-LSA
  Link State ID: 0
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000003
  Checksum: 0xF340
  Length: 64
  Referenced LSA Type: 2001
  Referenced Link State ID: 0
  Referenced Advertising Router: 2.2.2.2
  Number of Prefixes: 2
  Prefix Address: 2001:DB8::2:2:2:2
  Prefix Length: 128, Options: LA, Metric: 0
  Prefix Address: 2001:DB8:12::
  Prefix Length: 64, Options: None, Metric: 1

Here R2 has two prefixes in the LSA. R1 is also originating 2001:DB8:12::/64 in it’s LSA. When connected to a broadcast segment, routers do NOT advertise the connected prefixes address. Take a look at R7’s Type9:

R7#show ospfv3 database prefix self-originate

          OSPFv3 1 address-family ipv6 (router-id 7.7.7.7)

		Intra Area Prefix Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 6
  LS Type: Intra-Area-Prefix-LSA
  Link State ID: 0
  Advertising Router: 7.7.7.7
  LS Seq Number: 80000003
  Checksum: 0x2E11
  Length: 52
  Referenced LSA Type: 2001
  Referenced Link State ID: 0
  Referenced Advertising Router: 7.7.7.7
  Number of Prefixes: 1
  Prefix Address: 2001:DB8::7:7:7:7
  Prefix Length: 128, Options: LA, Metric: 0

R7 is not showing it’s connected to the 2001:db8:13::/64 subnet.

Responsibility for advertising that Type9 lies with the DR. The interesting part is that the DR actually originates two separate Type9s:

R3#show ospfv3 database prefix self-originate

          OSPFv3 1 address-family ipv6 (router-id 3.3.3.3)

		Intra Area Prefix Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 876
  LS Type: Intra-Area-Prefix-LSA
  Link State ID: 0
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000004
  Checksum: 0xE984
  Length: 52
  Referenced LSA Type: 2001
  Referenced Link State ID: 0
  Referenced Advertising Router: 3.3.3.3
  Number of Prefixes: 1
  Prefix Address: 2001:DB8::3:3:3:3
  Prefix Length: 128, Options: LA, Metric: 0

  Routing Bit Set on this LSA
  LS age: 1150
  LS Type: Intra-Area-Prefix-LSA
  Link State ID: 2048
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0x1297
  Length: 44
  Referenced LSA Type: 2002
  Referenced Link State ID: 2
  Referenced Advertising Router: 3.3.3.3
  Number of Prefixes: 1
  Prefix Address: 2001:DB8:13::
  Prefix Length: 64, Options: None, Metric: 0

There is an important detail to note. The Type9 originated for the segment has a reference LSA Type value of 2002 while a regular Type9 has a value of 2001. The 2002 value tells you that the LSA was originated by the DR for the segment.

Ultimately this means that a DR will originate two separate LSAs for each broadcast segment. The second LSA being the link state Type2:

R3#show ospfv3 database network self-originate

          OSPFv3 1 address-family ipv6 (router-id 3.3.3.3)

		Net Link States (Area 0)

  LS age: 1524
  Options: (V6-Bit, E-Bit, R-bit, DC-Bit)
  LS Type: Network Links
  Link State ID: 2 (Interface ID of Designated Router)
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000002
  Checksum: 0xF0D8
  Length: 36
	Attached Router: 3.3.3.3
	Attached Router: 1.1.1.1
	Attached Router: 7.7.7.7

In part 3 I’ll be going over inter-area LSAs

Read part 1
Read part 2
Read part 3
Read part 4

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