OSPF Required Information

Before starting, take the time to gather all of the information required to form an OSPF adjacency to a neighbor. At a minimum, FRR will need to know these items:

Local Router ID:

Typically the highest numbered local address on the firewall. This is also frequently set as the internal or LAN side IP address of a router. It does not matter what this ID is, so long as it is given in IPv4 address notation and does not conflict with any neighbors.

Local OSPF Area:

A designation for the set of networks to which this router belongs. Can be any number capable of being expressed in dotted quad notation (IPv4 address) or as a 32-bit unsigned integer.

In typical OSPF configurations such as this example, 0.0.0.0 is the backbone area between all routers and each local network has its own area. For simpler deployments, the only area may be 0.0.0.0 on every router and interface. Using a single area disables some features such as route summarization.

OSPF Active Interfaces:

The interfaces on this router upon which the OSPF daemon will advertise itself and look for neighbors. These interfaces are connected to network segments with other routers. They may be connected to local networks or remote point-to-point links. These interfaces must be configured with IP addresses.

OSPF Active Interface Cost Values:

OSPF calculates the most efficient way to route between networks based on the total cost of a path from source to destination. Less desirable links (e.g. wireless) can be given a higher cost so that paths over faster networks will be used by traffic unless the preferred path is unavailable. For single connections to other networks, this value is not necessary and may be omitted or set to a simple default such as 5 or 10.

OSPF Passive Interfaces:

These interfaces contain networks which should be advertised as reachable through this router, but do not contain other routers.

Summary Routes:

A list of networks to advertise instead of using networks from directly attached interfaces. This allows many similar routes to be summarized as one larger route if they can all be contained within a larger subnet.

This can only be done when connecting to an ABR in a configuration with multiple areas.

Note

This is optional, but without this in place, every network which must be advertised to neighbors must be attached to this firewall and the interfaces must be added as passive interfaces in OSPF. Using a summary route is cleaner in that it advertises less (one large subnet vs many small subnets) and that it requires less ongoing configuration.

The example in this section uses the following values:

Example OSPF Configuration

Item	Value
Local Router ID	10.2.0.1
OSPF Backbone Area	0.0.0.0
Local OSPF Area	0.0.0.2
Active Interfaces (Cost)	OPT1 (10)
Passive Interfaces	LAN
Summary Routes	10.2.0.0/16