This part covers Single-Area OSPFv2 (Area 0) configuration across the 6-node Nokia SR OS topology, verification of neighbor adjacencies, route table population, and LSDB behavior with point-to-point and broadcast network types.

  • SR OS Version: 25.7.R1

  • CLI Mode: MD-CLI (Model-Driven CLI)

Topology Diagram

Nokia SR OS OSPF Topology

Configuration

Enable OSPF instance 0 in Area 0 across all nodes. Configure physical and system interfaces as point-to-point, set system interfaces as passive to advertise loopback reachability without sending unnecessary Hello packets, and secure adjacencies with MD5 authentication.

Router R1 (CE1)

/configure router ospf 0 admin-state enable
/configure router ospf 0 area 0 interface "system" interface-type point-to-point
/configure router ospf 0 area 0 interface "system" passive true
/configure router ospf 0 area 0 interface "toR2" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR2" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR2" message-digest-key 1 md5 NokiaOSPF2026

commit

Router R2 (PE1)

/configure router ospf 0 admin-state enable
/configure router ospf 0 area 0 interface "system" interface-type point-to-point
/configure router ospf 0 area 0 interface "system" passive true
/configure router ospf 0 area 0 interface "toR1" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR1" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR1" message-digest-key 1 md5 NokiaOSPF2026
/configure router ospf 0 area 0 interface "toR3" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR3" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR3" message-digest-key 1 md5 NokiaOSPF2026
/configure router ospf 0 area 0 interface "toR4" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR4" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR4" message-digest-key 1 md5 NokiaOSPF2026

commit

Router R3 (P1)

/configure router ospf 0 admin-state enable
/configure router ospf 0 area 0 interface "system" interface-type point-to-point
/configure router ospf 0 area 0 interface "system" passive true
/configure router ospf 0 area 0 interface "toR2" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR2" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR2" message-digest-key 1 md5 NokiaOSPF2026
/configure router ospf 0 area 0 interface "toR5" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR5" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR5" message-digest-key 1 md5 NokiaOSPF2026

commit

Router R4 (P2)

/configure router ospf 0 admin-state enable
/configure router ospf 0 area 0 interface "system" interface-type point-to-point
/configure router ospf 0 area 0 interface "system" passive true
/configure router ospf 0 area 0 interface "toR2" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR2" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR2" message-digest-key 1 md5 NokiaOSPF2026
/configure router ospf 0 area 0 interface "toR5" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR5" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR5" message-digest-key 1 md5 NokiaOSPF2026

commit

Router R5 (PE2)

/configure router ospf 0 admin-state enable
/configure router ospf 0 area 0 interface "system" interface-type point-to-point
/configure router ospf 0 area 0 interface "system" passive true
/configure router ospf 0 area 0 interface "toR3" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR3" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR3" message-digest-key 1 md5 NokiaOSPF2026
/configure router ospf 0 area 0 interface "toR4" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR4" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR4" message-digest-key 1 md5 NokiaOSPF2026
/configure router ospf 0 area 0 interface "toR6" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR6" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR6" message-digest-key 1 md5 NokiaOSPF2026

commit

Router R6 (CE2)

/configure router ospf 0 admin-state enable
/configure router ospf 0 area 0 interface "system" interface-type point-to-point
/configure router ospf 0 area 0 interface "system" passive true
/configure router ospf 0 area 0 interface "toR5" interface-type point-to-point
/configure router ospf 0 area 0 interface "toR5" authentication-type message-digest
/configure router ospf 0 area 0 interface "toR5" message-digest-key 1 md5 NokiaOSPF2026

commit

Verification

Verifying OSPF Interfaces

Verify that all active physical links and system loopbacks show operational state PToP (show router ospf interface):

  • Router R2 (PE1):

R2 Interface Verification

  • Router R3 (P1):

R3 Interface Verification

Checking Adjacency States

With point-to-point network types configured, OSPF bypasses DR/BDR election and transitions directly to Full adjacency:

  • R1 (CE1): 1 full adjacency (toR2)
  • R2 (PE1): 3 full adjacencies (toR1, toR3, toR4)
  • R3 (P1) & R4 (P2): 2 full adjacencies each
  • R5 (PE2): 3 full adjacencies (toR3, toR4, toR6)
  • R6 (CE2): 1 full adjacency (toR5)

Neighbor Verification Example: Router R2 (PE1)

R2 Neighbor Verification

Validating End-to-End Reachability

Verify OSPF and global routing tables on R1 (CE1). Remote loopbacks and transit subnets are learned dynamically via OSPF:

  • OSPF Route Table Inspection (R1):

R1 OSPF Routes Verification

  • Global Route Table Inspection (R1):

R1 Route Table Verification

Verify end-to-end data plane reachability across the core by pinging R6’s system loopback (10.100.1.6) from R1 (R1 → R2 → R3/R4 → R5 → R6):

R1 Pinging R6 system interface

LSDB Analysis

Inspect Link-State Database (LSDB) contents across the topology, then observe how changing the interface network type from point-to-point to broadcast alters LSA generation and triggers DR/BDR elections.

Once OSPF converges, every router maintains an identical LSDB copy containing entries corresponding to each router’s system ID:

  • Database Inspection on R1:

    R1 OSPF Database Verification

  • Database Inspection on R5:

    R5 OSPF Database Verification

2. Detailed LSA Inspection

Inspecting a Router LSA (e.g., from R1 (CE1) via 10.100.1.1) details how physical topology (neighbors) and IP reachability (adjacent subnets) are advertised:

R1 Detailed OSPF Database Verification

3. Changing Interface Types: Point-to-Point to Broadcast

Change the network type on the link between R1 (CE1) and R2 (PE1) from point-to-point to broadcast:

  • On R1:
/configure router ospf 0 area 0 interface "toR2" interface-type broadcast

commit
  • On R2:
/configure router ospf 0 area 0 interface "toR1" interface-type broadcast

commit

4. Broadcast Verification

Once committed on both routers, OSPF initiates a DR/BDR election:

  • Router R1 (CE1) Interface State: R1 Interface Verification - Broadcast

  • Router R2 (PE1) Interface State: R2 Interface Verification - Broadcast

    The operational interface state transitions from PToP to either DR or BDR.

  • Router R1 (CE1) Database State: R1 Database Inspection - Broadcast

    A Network LSA (Type 2) is generated and injected into the LSDB by the elected Designated Router, representing the transit broadcast segment and listing all adjacent routers.