Re: [OSPF] OSPF GR query

Abhay D.S Tue, 05 Dec 2006 18:05:49 -0800

hi acee,

Helper terminating graceful restart by flooding an inconsistent routeror network LSA

can cause increased downtime.

It is exactly good IMHO to have explicit notification back to re-starterfirst.

The idea is with due respect to the critical interdependencies on OSPFrouting on otherprotocols, and how long we might allow and watch to flap, wrench andwrestle all the signalling, routing,and other data protocols which depend on OSPF in the event of a helpernot co-operating.

This idea is above all the reason of whether to include this mechanismin grat(c)eful re-start.


It rather completes a old gr specification    ;-).

Thanks,
Abhay


Acee Lindem wrote:

Hi Sujay,
sujay gupta wrote:

Hi Acee,
A late mail on this thread.

given the scenario if R3-R1 is a stub area
and the incoming LSA is a type-5, even with strict LSA
checking enabled will not exit Helper mode.

I'm not sure what the network picture looks like but a helper
router can always terminate graceful restart by flooding an
inconsistent router or network LSA to the restarting  router.

Thanks,
Acee


It can be a nice idea to give some explicit notification
by R2 to R1 about exiting helper mode.

As rightly pointed by you the above conditions and more
has been causing some confusion for some time.
Our proposal ;

http://tools.ietf.org/wg/ospf/draft-holla-ospf-update-graceful-restart-02.txt

hopefully resolves this.
Could we add this as an addendum/reference to RFC3623?, purely an
add-on.
Best Regards.
Sujay

On 10/5/06, Acee Lindem <[EMAIL PROTECTED]> wrote:


Khan Amir-G20247 wrote:
> Hi Ace
>

> But reaching to a FULL state is not one of the conditions forHelper to

> quit Helper mode, I guess a Helper who has reached

> to FULL state with its restarting router will wait for Grace LSAsto be

> flushed or GR timeout to happen for exiting Helper mode.
>

No - The presumption is when you reach FULL state you don't need to"quit"helping - you have "finished" helping. Over the years, there havebeen a

few situations that could have been better documented - however, this
never
caused any confusion in the past.

Thanks,
Acee

> Regards
> Aamir
>
>
> -----Original Message-----
> From: Acee Lindem [mailto:[EMAIL PROTECTED]
> Sent: Thursday, October 05, 2006 8:00 PM
> To: Khan Amir-G20247
> Cc: [email protected]
> Subject: Re: [OSPF] OSPF GR query
>
> Hello Amir,
>
> Khan Amir-G20247 wrote:
>
>>
>>
>> Hi
>>
>> I have query related to OSPF Graceful Restart.
>>
>> Consider this scenario:
>>
>>
>>
>> - Three Routers R1, R2 and R3 connected via Broadcast networks.
>>
>>
>>
>>
>>
>>
>>
>> - Where R1 is a DR on both the segments, where as R2 and R3 are in
>> DR-other
>> - Now R1 wants to perform GR, R2 and R3 agrees to be its Helpers.

>> - Now after restart R1 will try to form adjacency with both R2and R3.

>>
>
>
>> - Lets say R1 and R2 had become FULL, while R1 and R3 had reached

>> Exstart state. Now at this time R2 receives an LSA (any type1-5 and

>> 7, from some other router existing in the same area, not pictured
>> here) which he needs to flood to R1.

>> - This will force R2 to quit Helper Status, while R1 and R3 arestill

>> in process of forming adjacency.
>>
>>
> Since he has reached FULL state, he is no longer a helper router.
>
>> Considering above scenario, my doubts are:
>>
>> - How will R1 come to know that its Helper R2 has quit?
>>
>>
> Since he has reached FULL state, he is no longer a helper router.
>
>> - Will the adjacency between R1 and R2 needs to go down, as R2 quits
>> helper mode?
>>
>>
> No
>
>> - Will this effect the adjacency formation of R1 and R3?
>>
>>
> No. R3 MAY exit helper status and re-originate a new router LSA if he
> receives the new LSA before reaching FULL state with R1 AND he is has
> strict-LSA-checking configured.
>
> Hope this helps,
> Acee
>
>>
>>
>> Regards
>> Aamir
>>
>>
>>
>>
>>

>>----------------------------------------------------------------------

>> --
>>
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>>
>>
>

>

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