Re: Reestablish adjacencies after Graceful-Restart

[Debopam Bandyopadhyay <debopam at ALUMNUX.COM>]

Hi Acee,

Thanks a lot for the help.

Regards,
Debopam

>Hi Debopam,
>
>Debopam Bandyopadhyay wrote:
>
>>Thanks a lot for the help, Acee. It has cleared a major chunk of my design
>>requirements.
>>Finally, I have one question related to a hypothetical case (which may be
>>required for interoperability).
>>
>>I will go back to the previous example:
>>
>>            X ----- lan ----- Y
>>
>>In the topology, we have two routers, X and Y; and Y happens to be the DR
in
>>the network segment.
>>
>>Now Router X restarts. After 'T' seconds, Router X becomes fully adjacent
>>with Router Y.  'T is very much less than X's Grace Period.
>>Let's say, X is unable to trace its pre-restart Router-LSA in its database
>>(because Y had not sent it during the DD-exchange). So my question is:
>>1> Would X now exit Graceful-restart at this point, or
>>2> Would X wait for its pre-restart Router-LSA to be received from Y (in
the
>>form of LS-Updates), until grace period expires; or
>>3> Would it be implementation dependent?
>>
>>
>While not every scenario is not explicitly documented,  not having a
>pre-restart LSAs and
>a full neighbor would be fall into the category of an inconsistent LSA.
>Hence, you should
>terminate graceful restart as specified by 2) in section 2.2 of RFC
>3623. Keep in mind,
>that a full adjacency implies a complete database exchange.
>
>Hope this helps,
>Acee
>
>
>>Thanks,
>>Debopam
>>
>>----- Original Message ----- 
>>From: "Acee Lindem" <acee at CISCO.COM>
>>To: <OSPF at PEACH.EASE.LSOFT.COM>
>>Sent: Monday, May 09, 2005 5:50 PM
>>Subject: Re: Reestablish adjacencies after Graceful-Restart
>>
>>
>>Debopam Bandyopadhyay wrote:
>>
>>
>>
>>>This question is a bit long, backdated and maybe, queer. But it is a bit
>>>
>>>
>>critical for me.
>>
>>
>>>It is regarding RFC 3623 (Graceful OSPF Restart), Section 2.2. "When to
>>>
>>>
>>Exit Graceful Restart", Point 1 "Router X has reestablished all its
>>adjacencies".
>>
>>
>>>I am trying to identify the corresponding event from RFC 2328 for Router
X.
>>>
>>>
>>Is it one of the following:
>>
>>
>>>a> Upon installation of an LSA in the database [RFC2328, Sec 13.2] [and
>>>
>>>
>>thereby tracing the database for all the relevant LSAs which indicate the
>>previous adjacencies],
>>
>>
>>>    or
>>>b> State of neighbor Y changing to Full; [and thereby tracing the
database
>>>
>>>
>>...]
>>
>>
>>>    or
>>>c> Implementation specific
>>>
>>>Let me explain this with a simplified example:
>>>
>>>           X ----- lan ----- Y
>>>
>>>In the topology, we have two routers, X and Y; and Y happens to be the DR
>>>
>>>
>>in the network segment.
>>
>>
>>>Now Router X restarts. After 'T' seconds, Router X becomes fully adjacent
>>>
>>>
>>with Router Y.
>>
>>
>>>At this point, three scenarios are possible:
>>>1> X had received all the relevant LSAs (i.e. router-LSAs of X, Y and
>>>
>>>
>>Network-LSA of Y) BEFORE becoming fully adjacent with Y.
>>
>>
>>>    Hence, the graceful-restart exit event has already been fired BEFORE
X
>>>
>>>
>>became fully adjacent with Y.
>>
>>
>>>2> X had received all the relevant LSAs BEFORE becoming fully adjacent
with
>>>
>>>
>>Y;
>>
>>
>>>    but graceful-restart exit event gets fired EXACTLY when X became
fully
>>>
>>>
>>adjacent with Y.
>>
>>
>>>3> X had completed receiving all the relevant LSAs AFTER becoming fully
>>>
>>>
>>adjacent with Y;
>>
>>
>>>    Hence, the graceful-restart exit event gets fired sometime AFTER X
>>>
>>>
>>became fully adjacent with Y.
>>
>>
>>>
>>>
>>Hi Depopam,
>>
>>As stated in RFC 3623 section 2.2, a restarting router uses its
>>pre-restart router
>>LSA to determine whether or not it has re-established all its
>>pre-restart adjacencies.
>>Adjacency formation implies database synchronization and reception of
>>all LSAs within
>>the flooding domain of the router with whom the adjacency is being
>>formed. Hence,
>> #2 above is the only scenario which makes sense.
>>
>>Hope this helps,
>>Acee
>>
>>
>>
>>
>>>Thanks,
>>>Debopam
>>>
>>>
>>>
>>>
>>
>>
>>