Clearing OSPF routes from the routing table

If you think the wrong route has been added to your routing table and you want to check it out, you first have to remove that route from your table before seeing if it is added back in or not. You can clear all or some OSPF neighbor connections (sessions) using the execute router clear ospf command. The exec router clear command is much more limiting for OSPF than it is for BGP. See Border Gateway Protocol (BGP) on page 338.

For example, if you have routes in the OSPF routing table and you want to clear the specific route to IP address 10.10.10.1, you will have to clear all the OSPF entries. Enter the command:

execute router clear ospf process

Checking the state of OSPF neighbors

In OSPF each router sends out link state advertisements to find other routers on its network segment, and to create adjacencies with some of those routers. This is important because routing updates are only passed between adjacent routers. If two routers you believe to be adjacent are not, that can be the source of routing failures.

To identify this problem, you need to check the state of the OSPF neighbors of your FortiGate unit. Use the CLI command get router info ospf neighbor all to see all the neighbors for your FortiGate unit. You will see output in the form of:

FGT1 # get router info ospf neighbor

OSPF process 0:

Neighbor ID Pri State   Dead Time Address Interface

10.0.0.2    1   Full/ – 00:00:39 10.1.1.2 tunnel_wan1

10.0.0.2    1   Full/ – 00:00:34 10.1.1.4 tunnel_wan2

The important information here is the State column. Any neighbors that are not adjacent to your FortiGate unit will be reported in this column as something other than Full. If the state is Down, that router is offline.