OSPF multiple instances per link

‎08-09-2017 05:26 AM


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?


Regards, Wojtek



Re: OSPF multiple instances per link

‎08-11-2017 04:03 AM

I did some digging and it looks like they were talking about OSPFv2 Multi-Instance Extensions.


   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.

Am I right?


Regards, Wojtek


Re: OSPF multiple instances per link

‎08-15-2017 04:10 AM

Hi Wojtek,

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.

Please mark my solution as accepted it it helped.