Technical Tip: OSPFv3 error 'OSPFv3: RECV[Hello]: instance ID mismatch'

[kaurg_FTNT]

Description	This article explains the reason for the error 'OSPFv3: RECV[Hello]: instance ID mismatch' observed on FortiGate.
Scope	FortiGate.
Solution	OSPFv3 was developed to support IPv6. Instance ID is an 8-bit field in the OSPFv3 header. Instance ID was designed to facilitate multiple instances of OSPFv3 to run on a single interface. An instance number of 0 through 255 can be used to distinguish between the different OSPFv3 instances. Further Instance ID will tell more details on what type of routes will be advertised in OSPFv3 adjacency: 0 - 31 --> It is used to advertise IPv6 unicast. 32 - 63 --> It is used to advertise IPv6 multicast. 64 - 95 --> It is used to advertise IPv4 unicast. 96 - 127 --> It is used to advertise IPv4 multicast. 128 - 255 --> It is unassigned. At present, the 'Instance ID' feature is not supported on FOS, leading to an error in Routing events, as depicted below. The error message suggests that routers with disparate OSPF Instance IDs cannot form an adjacency. This issue arises due to a mismatched instance ID received from a peer, considering FortiGate's default interface instance is set to 0. It is important to note that the 'Instance ID' feature is currently not supported on FOS. However, there is a possibility of it being supported in future releases. For any further assistance, contact Fortinet support.