OSPF

OSPF (Open Shortest Path First) is a standards-based link-state interior gateway protocol that uses Dijkstra’s shortest path first algorithm to calculate optimal routes through a network topology stored in a synchronized link-state database. It provides fast convergence, load balancing across equal-cost paths, and hierarchical network design through area-based segmentation that reduces routing overhead and improves scalability in large networks. OSPF supports advanced features including route summarization, authentication, traffic engineering extensions, and integration with MPLS for comprehensive enterprise and service provider routing solutions.

Diagram

Classes

routing (iosxe.devices.configuration)

Name	Type	Constraint	Mandatory	Default Value
ospf_processes	List	`[ospf_processes]`	No

ospf_processes (iosxe.devices.configuration.routing)

Name	Type	Constraint	Mandatory
id	Integer	min: `1`, max: `65535`	No
vrf	String		No
bfd_all_interfaces	Boolean	`true`, `false`	No
default_information_originate	Boolean	`true`, `false`	No
default_information_originate_always	Boolean	`true`, `false`	No
default_information_originate_metric	Integer	min: `1`, max: `16777214`	No
default_information_originate_metric_type	Integer	min: `1`, max: `2`	No
default_information_originate_route_map	String		No
default_metric	Integer	min: `1`, max: `16777214`	No
distance	Integer	min: `1`, max: `255`	No
domain_tag	Integer	min: `1`, max: `4294967295`	No
fast_reroute_per_prefix_enable_prefix_priority	Choice	`high`, `low`	No
log_adjacency_changes	Boolean	`true`, `false`	No
log_adjacency_changes_detail	Boolean	`true`, `false`	No
max_metric_router_lsa	Boolean	`true`, `false`	No
max_metric_router_lsa_external_lsa_metric	Integer	min: `1`, max: `16777215`	No
max_metric_router_lsa_include_stub	Boolean	`true`, `false`	No
max_metric_router_lsa_on_startup_time	Integer	min: `5`, max: `86400`	No
max_metric_router_lsa_on_startup_wait_for_bgp	Boolean	`true`, `false`	No
max_metric_router_lsa_summary_lsa_metric	Integer	min: `1`, max: `16777215`	No
mpls_ldp_autoconfig	Boolean	`true`, `false`	No
mpls_ldp_sync	Boolean	`true`, `false`	No
neighbors	List	`[neighbors]`	No
networks	List	`[networks]`	No
nsf_cisco	Boolean	`true`, `false`	No
nsf_cisco_enforce_global	Boolean	`true`, `false`	No
nsf_ietf	Boolean	`true`, `false`	No
nsf_ietf_restart_interval	Integer	min: `1`, max: `3600`	No
priority	Integer	min: `0`, max: `127`	No
redistribute	Class	`[redistribute]`	No
router_id	IP		No
shutdown	Boolean	`true`, `false`	No
summary_addresses	List	`[summary_addresses]`	No
areas	List	`[areas]`	No
passive_interface_default	Boolean	`true`, `false`	No
auto_cost_reference_bandwidth	Integer	min: `1`, max: `4294967`	No
passive_interfaces	List	`[passive_interfaces]`	No
non_passive_interfaces	List	`[non_passive_interfaces]`	No
distribute_list_in	String		No
distribute_list_out	String		No

neighbors (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory
ip	IP		Yes
priority	Integer	min: `0`, max: `255`	No
cost	Integer	min: `1`, max: `65535`	No

networks (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory
ip	IP		Yes
wildcard	IP		No
area	Any	String or Integer[min: `0`]	No

redistribute (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory
connected	Boolean	`true`, `false`	No
connected_metric	Integer	min: `0`, max: `16777214`	No
connected_metric_type	Integer	min: `1`, max: `2`	No
connected_route_map	String		No
connected_tag	Integer	min: `0`, max: `4294967295`	No
static	Boolean	`true`, `false`	No
static_metric	Integer	min: `0`, max: `16777214`	No
static_metric_type	Integer	min: `1`, max: `2`	No
static_route_map	String		No
static_tag	Integer	min: `0`, max: `4294967295`	No
ospf	List	`[ospf]`	No

summary_addresses (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory	Default Value
ip	IP		Yes
mask	IP		No

areas (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory
id	Any	String or Integer[min: `0`]	No
authentication_message_digest	Boolean	`true`, `false`	No
nssa	Boolean	`true`, `false`	No
nssa_default_information_originate	Boolean	`true`, `false`	No
nssa_default_information_originate_metric	Integer	min: `0`, max: `16777214`	No
nssa_default_information_originate_metric_type	Integer	min: `1`, max: `2`	No
nssa_no_summary	Boolean	`true`, `false`	No
nssa_no_redistribution	Boolean	`true`, `false`	No

passive_interfaces (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory	Default Value
interface_type	Choice	`Loopback`, `Vlan`, `GigabitEthernet`, `TwoGigabitEthernet`, `FiveGigabitEthernet`, `TenGigabitEthernet`, `TwentyFiveGigabitEthernet`, `FortyGigabitEthernet`, `FiftyGigabitEthernet`, `HundredGigabitEthernet`	No
interface_id	Any	String or Integer[min: `0`]	No

non_passive_interfaces (iosxe.devices.configuration.routing.ospf_processes)

Name	Type	Constraint	Mandatory	Default Value
interface_type	Choice	`Loopback`, `Vlan`, `Tunnel`, `Port-channel`, `Port-channel-subinterface`, `GigabitEthernet`, `TwoGigabitEthernet`, `FiveGigabitEthernet`, `TenGigabitEthernet`, `TwentyFiveGigabitEthernet`, `FortyGigabitEthernet`, `HundredGigabitEthernet`, `TwoHundredGigabitEthernet`, `FourHundredGigabitEthernet`	No
interface_id	Any	String or Integer[min: `0`]	No

ospf (iosxe.devices.configuration.routing.ospf_processes.redistribute)

Name	Type	Constraint	Mandatory
process_id	Integer	min: `1`, max: `65535`	Yes
match_internal	Boolean	`true`, `false`	No
match_external_1	Boolean	`true`, `false`	No
match_external_2	Boolean	`true`, `false`	No
match_nssa_external_1	Boolean	`true`, `false`	No
match_nssa_external_2	Boolean	`true`, `false`	No
metric	Integer	min: `0`, max: `16777214`	No
metric_type	Integer	min: `1`, max: `2`	No
route_map	String		No
tag	Integer	min: `0`, max: `4294967295`	No
vrf	String		No

By using Dijkstra’s algorithm and area-based segmentation, OSPF provides fast convergence, scalable routing, and robust network design.

OSPF Parameters

Key Components:

OSPF Process ID (id): Identifies the OSPF routing process.
Router ID (router_id): Sets the unique router ID for the process.
Network Statements (networks): Advertises networks into OSPF with IP, wildcard mask, and area.
Area Type (areas): Configures area types (normal, stub, NSSA, totally stubby).
Interface Cost (neighbors.cost): Sets the cost for OSPF interfaces.
Interface Priority (neighbors.priority): Sets the priority for OSPF interfaces.
Authentication (areas.authentication_message_digest): Enables OSPF authentication (simple, MD5).
Default Information Originate (default_information_originate): Advertises a default route into OSPF. Supports default_information_originate_metric, default_information_originate_metric_type (1 or 2), and default_information_originate_route_map.
Redistribute (redistribute): Controls route redistribution into OSPF. Supports static and connected with optional metric, metric_type, route_map, and tag. Inter-process OSPF redistribution via ospf list with process_id, match options (match_internal, match_external_1, match_external_2), and common redistribution attributes.
Distribute List (distribute_list_in, distribute_list_out): Filters OSPF routing updates using a standard ACL applied inbound or outbound.
Route Summarization (summary_addresses): Configures inter-area and external route summarization.
Administrative Distance (distance): Sets the OSPF administrative distance.
Bidirectional Forwarding Detection (BFD) (bfd_all_interfaces): Enables BFD for OSPF interfaces.
Passive Interface (passive_interface_default, passive_interfaces, non_passive_interfaces): Configures passive interfaces. Use passive_interface_default with non_passive_interfaces to enable the common hardening pattern of making all interfaces passive by default and selectively re-enabling specific uplinks.
Reference Bandwidth (auto_cost_reference_bandwidth): Sets reference bandwidth for auto-cost calculation.
VRF Association (vrf): Associates OSPF process with a VRF.

Key Parameters Briefly Explained:

id: OSPF process identifier.
router_id: Unique router ID.
networks: Network statements for OSPF.
areas: Area configuration and types.
neighbors.cost, neighbors.priority: Interface cost and priority.
areas.authentication_message_digest: Authentication settings.
default_information_originate: Default route advertisement.
default_information_originate_metric, default_information_originate_metric_type: Default route metric options.
redistribute.static, redistribute.connected: Basic redistribution with optional metric, metric_type, route_map, tag.
redistribute.ospf: Inter-process OSPF redistribution with match options.
distribute_list_in, distribute_list_out: ACL-based route filtering.
summary_addresses: Route summarization.
distance: Administrative distance.
bfd_all_interfaces: BFD enablement.
passive_interface_default, passive_interfaces, non_passive_interfaces: Passive interface settings.
auto_cost_reference_bandwidth: Reference bandwidth.
vrf: VRF association.

You can use these OSPF parameters to design and implement a scalable and efficient routing infrastructure. Customize the process ID, router ID, network statements, area types, and interface settings to fit your network’s topology, performance requirements, and security policies. Adjusting these parameters lets you tailor OSPF’s behavior for optimal route calculation and distribution.

Sample Configuration

The following configuration describes how to set up OSPF on a Cisco IOS-XE device, including process definition, router ID, network advertisement, area configuration, default route origination, passive interfaces, and VRF association.

router ospf 100
 router-id 192.168.1.1
 bfd all-interfaces
 redistribute connected metric 200 metric-type 2 tag 600
 redistribute static metric 100 metric-type 1 tag 500 route-map RM_STATIC
 redistribute ospf 200 metric 150 metric-type 1 match internal external 1
 default-information originate always metric 10 metric-type 1
 auto-cost reference-bandwidth 10000
 network 192.168.1.0 0.0.0.255 area 0
 network 10.0.0.0 0.255.255.255 area 1
 distribute-list 10 in
 distribute-list 20 out
 passive-interface default
 no passive-interface GigabitEthernet0/0
 passive-interface Vlan100
 area 1 authentication message-digest
 area 1 nssa default-information-originate metric 100 metric-type 1 no-summary
!
router ospf 200 vrf VRF-PROD
 router-id 172.16.1.1
 default-metric 20
 network 172.16.0.0 0.0.255.255 area 0

Example YAML Code

The following YAML code defines OSPF configuration on an IOS-XE device, including multiple OSPF processes, VRF association, BFD settings, default route origination, auto-cost reference bandwidth, neighbor configuration, networks, router ID, summary addresses, area types, and passive interface settings.

iosxe:
  devices:
    - name: Device1
      configuration:
        routing:
          ospf_processes:
            - id: 100
              vrf: VRF-PROD
              bfd_all_interfaces: true
              default_information_originate: true
              default_information_originate_always: true
              default_metric: 10
              distance: 120
              domain_tag: 10
              auto_cost_reference_bandwidth: 10000
              neighbors:
                - ip: 192.168.1.2
                  priority: 10
                  cost: 100
                - ip: 192.168.2.2
                  priority: 5
                  cost: 50
              networks:
                - ip: 192.168.1.0
                  wildcard: 0.0.0.255
                  area: "0"
                - ip: 10.0.0.0
                  wildcard: 0.255.255.255
                  area: "1"
              router_id: 192.168.1.1
              shutdown: false
              summary_addresses:
                - ip: 10.0.0.0
                  mask: 255.0.0.0
                - ip: 172.16.0.0
                  mask: 255.240.0.0
              areas:
                - id: "1"
                  authentication_message_digest: true
                  nssa: true
                  nssa_default_information_originate: true
                  nssa_default_information_originate_metric: 100
                  nssa_default_information_originate_metric_type: 1
                  nssa_no_summary: true
                  nssa_no_redistribution: true
              passive_interface_default: true
              passive_interfaces:
                - interface_type: GigabitEthernet
                  interface_id: "0/0/1"
                - interface_type: Vlan
                  interface_id: "100"
              non_passive_interfaces:
                - interface_type: GigabitEthernet
                  interface_id: "0/0/0"
                - interface_type: GigabitEthernet
                  interface_id: "0/0/2"
            - id: 200
              bfd_all_interfaces: false
              default_metric: 20
              auto_cost_reference_bandwidth: 1000
              networks:
                - ip: 172.16.0.0
                  wildcard: 0.0.255.255
                  area: "0"
              router_id: 172.16.1.1
              passive_interface_default: false
            - id: 300
              log_adjacency_changes: true
              nsf_cisco: true
              nsf_cisco_enforce_global: true
              max_metric_router_lsa: true
              max_metric_router_lsa_summary_lsa_metric: 16711680
              max_metric_router_lsa_external_lsa_metric: 16711680
              max_metric_router_lsa_include_stub: true
              max_metric_router_lsa_on_startup_time: 60
              fast_reroute_per_prefix_enable_prefix_priority: high
              redistribute:
                connected: true
                connected_metric: 200
                connected_metric_type: 2
                static: true
                static_metric_type: 1
                static_route_map: RM_STATIC
                static_tag: 500
                ospf:
                  - process_id: 200
                    match_internal: true
                    match_external_1: true
                    metric: 150
                    metric_type: 1
                    route_map: RM_OSPF_REDIST
              distribute_list_in: "10"
              distribute_list_out: "20"
        interfaces:
          loopbacks:
            - id: 100
              description: OSPF multi-area interface
              ipv4:
                address: 192.168.100.1
                address_mask: 255.255.255.255
              ospf:
                process_ids:
                  - id: 300
                    areas:
                      - 0
                multi_area_ids:
                  - 10
                  - 20

Interface OSPF Authentication

OSPF supports three interface-level authentication modes. These are mutually exclusive — only one can be set per interface.

Key-Chain Authentication

References a key chain (configured via key_chains) for cryptographic authentication, supporting algorithm rotation and key lifetimes.

interface Loopback100
 ip ospf authentication key-chain OSPF-AUTH
 ip ospf 1 area 0

iosxe:
  devices:
    - name: Device1
      configuration:
        interfaces:
          loopbacks:
            - id: 100
              ospf:
                authentication_key_chain: OSPF-AUTH
                process_ids:
                  - id: 1
                    areas:
                      - 0

Message-Digest (MD5) Authentication

Enables MD5 authentication on the interface. Requires message_digest_keys to define the key ID and password.

interface Loopback101
 ip ospf authentication message-digest
 ip ospf message-digest-key 1 md5 md5pass123
 ip ospf 1 area 0

iosxe:
  devices:
    - name: Device1
      configuration:
        interfaces:
          loopbacks:
            - id: 101
              ospf:
                authentication_message_digest: true
                message_digest_keys:
                  - id: 1
                    md5_auth_key: md5pass123
                    md5_auth_type: "0"
                process_ids:
                  - id: 1
                    areas:
                      - 0

Null Authentication

Explicitly disables authentication on a specific interface, even when area-level authentication is enabled.

interface Loopback102
 ip ospf authentication null
 ip ospf 1 area 0

iosxe:
  devices:
    - name: Device1
      configuration:
        interfaces:
          loopbacks:
            - id: 102
              ospf:
                authentication_null: true
                process_ids:
                  - id: 1
                    areas:
                      - 0