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OSPFPrivileged EXEC

show ip ospf database

Displays the OSPF link-state database (LSDB) to verify OSPF adjacencies, check for missing or corrupt LSAs, and troubleshoot OSPF routing issues.

Syntax·Privileged EXEC
show ip ospf database

When to Use This Command

  • Verify that all expected LSAs (Type 1, 2, 3, etc.) are present in the LSDB after configuring OSPF.
  • Troubleshoot missing routes by checking if Type 3 summary LSAs are being generated by the ABR.
  • Confirm that an ASBR is advertising external routes by looking for Type 5 LSAs.
  • Check the age and sequence number of LSAs to detect OSPF instability or flapping neighbors.

Command Examples

Basic OSPF Database Display

show ip ospf database
       OSPF Router with ID (192.168.1.1) (Process ID 1)

                Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
192.168.1.1     192.168.1.1     345         0x80000004 0x00B2D4 2
192.168.1.2     192.168.1.2     567         0x80000003 0x00A1C3 3

                Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.1.3     192.168.1.3     234         0x80000001 0x0099E1

                Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.0.0        192.168.1.2     123         0x80000002 0x00CC44

                Summary ASB Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.2.1     192.168.1.2     456         0x80000001 0x00DD55

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
0.0.0.0         192.168.2.1     789         0x80000001 0x00EE66 0

The output is organized by LSA type. 'Router Link States' shows Type 1 LSAs from each router (identified by Link ID = Router ID). 'Net Link States' shows Type 2 LSAs from the DR (Link ID = DR's interface IP). 'Summary Net Link States' shows Type 3 LSAs from ABRs. 'Summary ASB Link States' shows Type 4 LSAs (ASBR summary). 'Type-5 AS External Link States' shows external routes. Key fields: ADV Router (advertising router), Age (seconds since LSA originated, should be < 1800 for stability), Seq# (increments with each update; higher is newer), Checksum (integrity check).

Display OSPF Database for a Specific LSA Type

show ip ospf database router 192.168.1.1
       OSPF Router with ID (192.168.1.1) (Process ID 1)

                Router Link States (Area 0)

  LS age: 345
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 192.168.1.1
  Advertising Router: 192.168.1.1
  LS Seq Number: 80000004
  Checksum: 0xB2D4
  Length: 48
  Number of Links: 2

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 192.168.1.3
     (Link Data) Router Interface address: 192.168.1.1
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 192.168.1.0
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

This shows detailed information for a specific Type 1 LSA. 'LS age' should be low (<1800) for a stable network. 'Link State ID' and 'Advertising Router' identify the originator. 'Number of Links' shows how many interfaces are participating in OSPF. Each link entry describes the type (transit, stub, etc.), the neighbor's DR address, and the metric (cost). A high age or rapidly changing Seq# may indicate instability.

Understanding the Output

The 'show ip ospf database' command displays the entire OSPF link-state database, organized by LSA type. Each section corresponds to a different LSA type: Type 1 (Router), Type 2 (Network), Type 3 (Summary), Type 4 (ASBR Summary), and Type 5 (External). The 'Link ID' field identifies the LSA's origin (e.g., Router ID for Type 1, DR's interface IP for Type 2). 'ADV Router' is the router that originated the LSA. 'Age' is the time in seconds since the LSA was first created; values approaching 1800 (MaxAge) indicate the LSA is about to be flushed. 'Seq#' is a sequence number that increments with each update; a higher number means a more recent LSA. 'Checksum' is used for error detection. In a stable network, ages should be relatively low and consistent, and sequence numbers should not be jumping erratically. Missing or incomplete sections can indicate adjacency problems or misconfigurations (e.g., no Type 3 LSAs if ABR is not working).

CCNA Exam Tips

1.

CCNA exam tip: Know that Type 1 LSAs are generated by every router, Type 2 by the DR, Type 3 by ABRs, Type 4 by ABRs for ASBRs, and Type 5 by ASBRs.

2.

CCNA exam tip: The 'show ip ospf database' command is used to verify that the LSDB is synchronized; if an LSA is missing, the route will not be in the routing table.

3.

CCNA exam tip: In the exam, you may be asked to identify which router is the DR based on Type 2 LSA output (the Link ID is the DR's interface IP).

4.

CCNA exam tip: A high 'Age' value (close to 1800) indicates the LSA is about to expire; if it resets to 0, the LSA was refreshed. Frequent refreshes may indicate a flapping link.

Common Mistakes

Mistake 1: Confusing 'Link ID' with 'ADV Router' — the Link ID identifies the object (e.g., router ID or network), while ADV Router is the router that sent the LSA.

Mistake 2: Assuming that missing Type 5 LSAs mean no external routes exist — check if the ASBR is properly configured and reachable.

Mistake 3: Ignoring the 'Age' field — if ages are consistently high or vary wildly, it may indicate OSPF instability or a router with a bad clock.

Related Commands

show ip ospf

Displays general information about OSPF routing process, including router ID, areas, and LSDB statistics, used to verify OSPF configuration and operational status.

show ip ospf neighbor

Displays OSPF neighbor information to verify adjacency formation and troubleshoot OSPF neighbor relationships.

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