I85PREP
⌘ K
Nokia 4A0-113 OSPF study materials
Nokia 4A0-113 OSPF study resources

Nokia 4A0-113 OSPF: Link-State Database, LSAs, and Area Types

Nokia 4A0-113 OSPF · Work through your exam, one topic at a time.

All guide sections

Link-State Database, LSAs, and Area Types

Domain 3 - Link-State Database, LSAs, and Area Types

This domain tests the LSA types, which router floods which LSA, and how area types filter them.

LSA types

  • Type 1 Router: one per router per area; describes links and costs.
  • Type 2 Network: generated by the DR for a broadcast segment.
  • Type 3 Summary: ABR advertises prefixes from another area.
  • Type 4 ASBR Summary: ABR tells the area where the ASBR is.
  • Type 5 External: ASBR floods external prefixes across the domain.
  • Type 7 NSSA External: used inside an NSSA; the ABR translates it to Type 5 at the area boundary. LSAs have a sequence number, age, and checksum; the LSDB must be identical within an area.

Area types

  • Normal: all LSA types.
  • Stub: blocks Type 5 and Type 4; the ABR injects a default route.
  • Totally stubby: also blocks Type 3, leaving only intra-area routes and the default.
  • NSSA: blocks Type 5 but allows Type 7, so external routes can be originated inside.
  • Totally NSSA: blocks Type 3 and Type 5, allows Type 7.

Worked example

Area 1 is stub and contains R1. The ABR has an external 192.0.2.0/24 from area 0. R1's LSDB contains Type 1 and Type 2 LSAs from area 1, Type 3 summaries for inter-area prefixes, and a default Type 3 from the ABR - but no Type 5 for 192.0.2.0/24. R1 reaches it via the default.

Traps

Thinking stub areas receive external routes with a metric. Forgetting Type 4 exists. Assuming a stub router can be an ASBR - it cannot. Mixing up Type 7 translation and Type 7 flooding.