In the old JNCIP materials I found a sentence saying about one of differences between OSPFv2 and OSPFv3
Support for multiple instances per link: This support allows multiple OSPF instances to run over a single link to support separate routing domains or to support a single link belonging to multiple areas. Previously, this functionality was achieved in OSPFv2 by tweaking authentication to hide OSPF packets from an OSPF router. This functionality is now formalized by including an instance ID in the OSPF header.
Does anybody have an example of this authentication tweak?
This document defines the OSPFv2 Instance ID to enable separate OSPFv2 protocol instances on the same interface. Unlike OSPFv3 where the Instance ID can be used for multiple purposes, such as putting the same interface in multiple areas, the OSPFv2 Instance ID is reserved for identifying protocol instances.
This document extends OSPFv2 with a mechanism to differentiate packets for different instances sent and received on the same interface. In support of this capability, a modified packet header format with the Authentication Type field split into an Instance ID and AuType.
This is not about Junos configuration tweak but a protocol implementation tweak.
As far as I know the only way to run multiple OSPF instances in Junos is to use routing instances. Since single interface cannot be configured under multiple routing instances there is no way to use this functionality in Junos.
After reading some content I think your understanding is correct. Probably the tweak in the authentication mentioned in the Juniper document is the reduction in AuType OSPFv2 header field from 2 octets to 1 octet for Instance ID.
Regards, Rahul Please mark my solution as accepted it it helped.