Subject: [OSPF] OSPFv3: Clarification on instance ID

From: "Goyal, Manoj" <[email-masked]>
Date: Thu, 3 Aug 2006 12:50:49 -0700

Hi,
The paragraph:

   "In the context of this document, an OSPF instance is a separate
   protocol instance complete with its own protocol data structures
   (e.g., areas, interfaces, neighbors), link state database, protocol
   state machines, and protocol processes (e.g.  SPF calculation)."

but in the rest of the document it says that the instance ID has
local link significance only and it solely affects the reception of
the packets.
It can also be used to have one link in more then one area.

Also:
   "Additionally, an instance ID
   may be configured for virtual links from different protocol instances
   in order to utilize the same transit area (without requiring
   different router IDs for demultiplexing)."

Lets look at these situations here.
There are three OSPF processes running on a system:

OSPF instance A :
   interface-1      inst-ID 10
   interface-2      inst-ID 20

OSPF instance B :
   interface-1      inst-ID 11
   interface-2      inst-ID 21
   interface-3      inst-ID 31

OSPF instance C :
   interface-1      inst-ID 12 Area 1
   interface-1      inst-ID 13 Area 2

- If the instance ID has local link significance only then all the above
  configurations should be valid.(??)

- But, if the instance ID means that the SPF will be run only on the
  packets with the same instance ID, essentially mandating that
  one ospf process(instance) should really have all the interfaces
  in it assigned the same instance ID, then these configs are invalid.
  In this case, the same interface can not be used in more then one area
  of the same instance.

What are your views?

thanks,
Manoj
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