Technical Tip: How to redistribute a default route in OSPF

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Description	This article provides explanations on how to redistribute the default route in OSPF with different metrics, so the peer will get the route with a lower than the default metric of 10.
Scope	FortiGate.
Solution	The following syntax is used to advertise a default route in OSPF on a FortiGate. config router ospf(ospf)  set default-information-originate <option> Available options are as follows: 'enable': Enable setting.                 <- This will send a default route if FortiGate has one in the routing table. 'always': Always advertise the default router.     <- This will always send a default route. 'disable': Disable setting. To prevent advertising a default route to some OSPF neighbors behind specific OSPF interfaces: Do not enable OSPF on those interfaces if this is possible (a static default route towards the ISPs routers might be enough in most cases). Set those interfaces as passive interfaces if the subnet has to be advertised as OSPF routes but is not forming an adjacency. In the GUI, note the same options: By default, the redistributed default route is with the metric of 10. In order to change the metric for the default route, use the following options (CLI): config router ospf     set default-information-originate enable    set default-information-metric 1  <- It is possible to use metric if needed. set default-information-metric-type type 1 | type2 Type 1 (E1): Metric increases as it moves through the OSPF domain (cumulative cost). Type 2 (E2 - Default): Metric remains constant, regardless of path cost. The result is the following external LSA generated from the advertising FortiGate: AS External Link States.  LS age: 551  Options: 0x2 (*|-|-|-|-|-|E|-)  LS Type: AS-external-LSA  Link State ID: 0.0.0.0 (External Network Number)  Advertising Router: 172.16.20.2  LS Seq Number: 80000001  Checksum: 0xb475  Length: 36  Network Mask: /0        Metric Type: 2                  <- Larger than any link state path.    TOS: 0        Metric: 1        Forward Address: 10.200.1.1        External Route Tag: 0 In the routing table of the peer, it is possible to confirm that the route is with a metric of 1: get router info routing-table data Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP       O - OSPF, IA - OSPF inter area       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2       E1 - OSPF external type 1, E2 - OSPF external type 2       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area       > - selected route, * - FIB route, p - stale info Routing table for VRF=0O E2    0.0.0.0/0 [110/1] via 10.200.1.1, port1, 00:22:17 S    *> 0.0.0.0/0 [10/0] via 172.16.31.254, port10 Run the following command to check if the default route is advertised: show router ospf database external Note: By default, FortiGate does not advertise an inactive route (routes which are not present in the routing table). Related articles: Technical Tip: OSPF configuration guide for ABR and ASBR settings Technical Tip: simple OSPF configuration with 2 FortiGates in the same area Technical Tip: OSPF route summarization for LSAs Type 3 (on ABR) and Type5 (on ASBR) Technical Tip: How to redistribute routes from other sources in a dynamic routing protocol (RIP, OSP... Technical Tip: OSPF static route redistribution example