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From: Erblichs (erblichs_at_EARTHLINK.NET)
Date: Tue Oct 01 2002 - 12:46:10 CDT
I haven't seen whether last year's RFC on Out-of-band
LSDB Resynchronization draft had been formalized into a
So these comments may be way late, with this
different approach to perform LSDB Resynchronization.
I haven't tried this .... but in my mind this
method could accomplish the same thing with
legacy routers and remove the need for a
option bit which is becoming a scarse thing
in version 2. And be a lightweight mechanism.
Since the neighbor field in a hello PDU is the
normal indicator of 2-way communication, why
not just temporarily drop the neighbor field
of the adjacency that you wish to re-establish?
Yes, I am assuming that based on your internal
request to perform this operation you reset
your neighbor state machine and set a internal
"OOB request neighbor field flag".
At best you can re-establish the link on average
of 1/2 hello interval and at worst you will have
to wait router-dead-interval timeframe before
you re-acknowledge the arrival of hellos from
the neighbor that you wish resync the adjacency.
(or wait before you resend hellos?)
The preference is to just with-hold the neighbor
from the neighbor field. This would allow the
OOB requester to remain as a DR or BDR if that
was his orignal router OSPF type. This would
remove any necessary overhead of elections,
adjacency reformations, and substantial SPF
Then the question is how to utilize the flag
to make sure that you don't deallocate any
neighbor data structures and whether you increment
the sequence number of your orignated LSAs,
keep them the same, or set MAXAGE and then resend.
More than likely you will also have to withold
flooding to the neighbor or acks back to the
neighbor from his flooding of LSAs. If LSAs were
recv'ed from the neighbor during flooding, I would
probably incorporate them into my LSDB.
Independent of how you deal with the above issues,
you then must re-attempt to synchronize the LSDB.
Assuming that their were more than two OSPF speaking
routers in your area, your previous interaction should
have minimal effects on your neighbor. More than
likely, he had kept your earlier originated LSAs
in his database. And you just resync, upon reaching
full state again with the neighbor, you clear your
internal "OOB request neighbor field flag".
Is there a dual-behaviour (one who wants to redo the
initial LSDB synchronization and one who keeps the
established adj) achieved by establishing
a adjacency and then removing the neighbor specified
in the hello field that really requires the
OOB requestor in the scenario to cycle into a
period of router-dead-interval before sending out
new hellos AND ... ????
Flames now allowed....