OSPF Interface Configuration

OSPF interfaces are managed at Services > FRR OSPF on the Interface tab.

The Interfaces tab contains a list of current OSPF interfaces, if any, and controls to manage the entries (e.g. edit, delete). The Add button creates a new interface.

OSPF must use one or more interfaces to announce itself to neighbors and to receive announcements from neighbors. At least one interface must be configured and active in order to locate neighbors and form an adjacency.

The remaining sections on this page cover the various options available when creating or editing an interface entry.

Interface Options

Interface:

The interface to use with OSPF. Entries should be added for interfaces which connect to other routers (neighbors) as well as interfaces containing networks which should be advertised to OSPF neighbors.

Description:

Text describing the purpose of this interface in OSPF.

Network Type:

Manually configures a specific type of network used on a given interface, rather than letting OSPF determine the type automatically. This controls how OSPF behaves and how it crafts messages when using an interface.

Tip

Most environments will use either Broadcast mode (e.g. Ethernet) or Point-to-Point mode (e.g. VPNs).

Broadcast:

Broadcast networks, such as typical Ethernet networks, allow multiple routers on a segment and OSPF can use broadcast and multicast to send messages to multiple targets at once. OSPF assumes that all routers on broadcast networks are directly connected and can communicate without passing through other routers.

Non-Broadcast:

Non-broadcast networks support multiple routers but do not have broadcast or multicast capabilities. Due to this lack of support, neighbors must be manually configured using the Neighbor tab (OSPF Neighbor Configuration).

When using this mode, OSPF simulates a broadcast network using Non-Broadcast Multi-Access (NMBA) mode, but transmits messages to known neighbors directly.

Point-to-Multipoint:

Similar to Non-Broadcast mode, but connections to manually configured neighbors are treated as a collection of point-to-point links rather than a shared network. Similar to a point-to-point network, OSPF disables DR election.

Point-to-Point:

A point-to-point network links a single pair of routers. The interface is still capable of broadcast, and OSPF will dynamically discover neighbors. With this type of network, OSPF disables election of a DR.

Interface is Passive:

Configures the specified interface as passive. This prevents the interface from actively participating in OSPF, while still allowing OSPF to operate on networks connected to that interface. This is commonly used for local interfaces without other routers attached. OSPF will announce networks attached to passive interfaces as stub links.

Ignore MTU:

When present, OSPF will ignore the MTU advertised by neighbors and can still achieve a full adjacency when peers do not have matching MTU values.

Tip

If two neighbors are stuck in an ExStart state, that is typically from an MTU mismatch. If fixing the MTU mismatch is not viable, set this option on both sides.

OSPF Interface Handling

Metric:

A manual cost value to apply to this interface, rather than allowing automatic cost calculation to take place.

In situations where multiple paths are possible to the same destination, this allows OSPF to prefer one path over another when all else is equal.

Area:

This defines the interface as a member of the given area. If this is left blank, FRR will take the value set in Default Area.

Accept Filter:

When set, automatically configures lists behind the scenes to prevent this interface subnet from being advertised to, or received from, OSPF.

This can avoid problems seen in Multi-WAN deployments where there are multiple paths to a remote neighbor and a router can end up learning a route to itself across a VPN link, which is problematic.

Authentication

Configures authentication for OSPF neighbors on this interface. All routers connected to this interface must have identical authentication configurations. This can also be enabled in the area settings.

Authentication Type:

Sets the type of authentication to use in this area.

None:

Do not use authentication in this area. This is the default behavior, but may be explicitly configured to override the authentication configured for this area.

Message Digest (MD5 Hash):

Enables MD5 HMAC authentication for this area. This is stronger authentication than simple passwords.

Simple Password:

Enables simple password authentication for this area.

Password:

Password to use with Simple Password or key to use with Message Digest authentication.

This value must match all neighbors reachable through this interface. Simple passwords may be up to 8 characters, Message Digest passwords (keys) may be up to 16 characters.

Advanced

Router Priority:

A priority value, from 0-255, assigned to this router. When determining which router will become the Designated Router (DR), the router with the highest priority is more likely to be elected as the DR.

The default value is 1. The value 0 is special and will prevent this router from being chosen as DR.

Retransmit Interval:

The interval, in seconds from 1-65535, at which this router will retransmit Link State Request and Database Description messages. This is also known as the RxmtInterval timer in OSPF. Default value is 5.

Hello Interval:

The interval, in seconds from 1-65535, at which this router will send hello messages. This is also known as the HelloInterval timer in OSPF. Default value is 10. This timer should be set to the same value for all routers.

A lower value will result in faster convergence times, but will consume more resources.

Dead Interval:

Time, in seconds from 1-65535, without communication from a neighbor on this interface before considering it dead. This is also known as the RouterDeadInterval timer in OSPF. Default value is 40. This timer should be set to the same value for all routers.

Minimal Hello:

When active, the Dead Interval is forced to a value of 1 and OSPF will instead send this number of Hello messages each second. This allows for faster convergence, but will consume more resources.

Note

When set, this overrides the values of both Dead Interval and Hello Interval. Custom values configured in those fields will be ignored by OSPF.

BFD

When set, enables Bidirectional Forwarding Detection for OSPF on this interface.