| Description | This article describes how the OSPF default-information-metric type 1 and type 2 work when default-information-originate is enabled. |
| Scope | FortiGate, OSPF |
| Solution |
The default-information-originate option on the OSPF is to advertise a default route to the peering OSPF devices. It has 3 possible options posted below:
disable (default): Avoid to advertise a default route to OSPF peering devices. enable: Advertise a default route to OSPF peering devices if there is an active default route on the routing-table. always: Always advertise a default route to OSPF peering devices even if there is no active default route on the routing-table.
If this option is set to enable and always, there are 2 additional configurations that we can adjust to control the default route being advertised to its peering devices.
OSPF metric type has 2 options, Either Type 1 or Type 2. Here are more details about metric types 1 and 2:
If metric type 1 is selected the metric value of the default route that will be advertised on the network will be the sum of the internal OSPF cost and the value set on 'set default-information-metric <integer>'.
See the sample scenario below to see how metric type 1 and type 2 work. Network Diagram:
Scenario 1: Both are using metric type 1. The lowest metric value will be selected as the primary default route of the peering devices and the computation will be the sum of the internal OSPF cost and the value set on 'set default-information-metric <integer>'.
Router1 routing table: Router 1 will select the route that has the lower metric and will have the metric value of External OSPF Type1 route (the sum of the internal OSPF cost and the value set on 'set default-information-metric <integer>').
Scenario 2: Both are using metric type 2. The lowest metric value will be selected as the primary default route of the peering devices and the metric will be the value set on 'set default-information-metric <integer>'.
DC1: Default Metric value is set to 500 and Metric type is set to type 2.
DC2: Default Metric Value is set to 400 and Metric Type is set Type 2.
Router 1 routing table: Router 1 will select the route that has the lower metric and will have the metric value of the External OSPF Type2 route (the metric will be the value set on 'set default-information-metric <integer>').
Scenario 3: DC1 and DC2 have different Metric Types. DC1 has a Metric type of 1 with a Metric value of 500 while DC2 has a Metric type of 2 with a Metric value of 400.
Note: The device that receives a metric type 1 and 2 on different devices will always prefer the type 1 over a type 2 route for the same destination.
Router 1 routing table: Router 1 will choose the DC1 default route since it is using Metric Type 1.
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