OSPF is a link-state protocol that gathers information from all the routers in the neighboring areas and chooses the shortest path with minimum cost for the data to be transmitted. It can successfully manage the bandwidth of the network and easily work on complex networks. However, sometimes issues may arise causing problems for data transmission in the shortest path. It is important to identify the issues and find proper methods to troubleshoot them. The common issues faced by OSPF and ways they can be troubleshot is mentioned below.
- OSPF Neighbor Issues: This issue arises if there is a connection problem between the two devices and the shortest path can’t be determined by OSPF. To troubleshoot, you need to check a few parameters like if the devices are in the same subnet, are in the same area, and have unique router IDs. Some of the commands mentioned below are used to troubleshoot.
- show ip protocols – This command is used to verify and troubleshoot the OSPF’s global configuration.
- show ip ospf – It verifies the basic configuration information related to OSPF protocol. The output shows information about Router ID, SPF related information, and Area related information that is useful.
- show ip ospf interface – It can be used to see a particular interface or all interfaces configuration and check if it is participating in OSPF or not. It also provides other information such as –
- Interface IP address
- Which area the interface is connected to as they must be in the same area to establish a neighboring relationship.
- Router ID of the interface must be unique.
- The type of network
- The Designated Router and the Backup designated router in that OSPF segment.
- Hello and Dead timers
- Adjacency reason in case of multi access networks
- show ip ospf neighbor – This command is used to show the neighbor related information and study the neighbor data structure.
- OSPF Routing Table Issues: This issue arises when some of the contents of the table get removed and OSPF can’t function properly. You need to identify if some of the routes have been deleted or damaged in the routing table an adjacency check will be required and external LSA check if any damage was made to external routes information.
- show ip ospf database – This command displays two important information. One is the area to which the route is connected to and the number of other routers present in that area. Second is the network links found in that area. It shows LSA types, Link ID, advertising router, and age.
- show ip route ospf – It shows OSPF routes that were received from the neighbors and information about it like administrative distances and cost.
- OSPF INIT Issues: When a router is able to send “Hello” messages to the neighbor but the neighbor is unable to return back the “Hello” it is known as the INIT state. So if this issue arises we need to check the authentication used in both the devices, the physical cabling, and also the switch settings. The following command is used to check the authentication.
show ip ospf interface – This command verifies if the same authentication keys are configured by both the devices.
- ACL Issues: Sometimes ACL interferes with the functioning of the OSPF and you need to check if any routers are configured with the ACLs. The following command is used to check.
show ip interface – This command verifies if ACL is applied to the specific interface to which OSPF is also configured. If ACL is found, then it needs to be disabled and check if OSPF has started to work again.
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