Re: Exit-Graceful Restart Condition

[Padma Pillay-Esnault <[e-mail]>]

Kishore Rao wrote:

>----- Original Message ----- 
>From: "Padma Pillay-Esnault" <[e-mail]>
>To: <[e-mail]>
>Sent: Wednesday, May 25, 2005 11:54 AM
>Subject: Re: Exit-Graceful Restart Condition
>
>
>  
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>>Kishore Rao wrote:
>>
>>    
>>
>>>----- Original Message ----- 
>>>From: "Acee Lindem" <[e-mail]>
>>>To: <[e-mail]>
>>>Sent: Wednesday, May 25, 2005 10:10 AM
>>>Subject: Re: Exit-Graceful Restart Condition
>>>
>>>
>>>
>>>
>>>      
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>>>>Padma Pillay-Esnault wrote:
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>>>sujay wrote:
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>>>Hi All,
>>>>>>
>>>>>>Considering RFC3623, Graceful Restart for OSPF V2 I have a problem;
>>>>>>
>>>>>>Ex:
>>>>>>
>>>>>>(network)---- DUT ---- RTA
>>>>>>
>>>>>>(All in the same area)
>>>>>>
>>>>>>Assume DUT undergoes a Graceful-Restart, it sends out grace LSA's to
>>>>>>RTA and other routers in the 'network'
>>>>>>
>>>>>>At the instant RTA recvs the Grace-LSA it also goes down.
>>>>>>
>>>>>>Is there a way in the RFC 3623 specified as to how DUT could Detect
>>>>>>this topology change and Exit GR *before* grace period expiry??
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>>I do not think the RFC covers this case. You are in a double failure
>>>>>situation.
>>>>>
>>>>>I can think of a simple solution. When DUT reacquires its router-lsa.
>>>>>It can determine its previous
>>>>>neighbors. It can then decide that if within DeadRouterInterval that
>>>>>neighbor did not  respond
>>>>>to hellos to abort GR. This would be equivalent to the normal
>>>>>situation when a router goes down and its
>>>>>neigbors takes DeadInterval to bring down their adjacency
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>I agree completely with Padma. One point, if RTA comes back up and
>>>>originates a new router LSA
>>>>then the DUT will detect the inconsistency (as specified in RFC 3623)
>>>>with it's pre-restart LSA and
>>>>terminate graceful restart.
>>>>
>>>>
>>>>        
>>>>
>>>Acee,
>>>
>>>Will this work ?
>>>In case there is another router RTB, scan the Hello from RTB for all
>>>neighbors on the network and then make sure Hello from RTA has been
>>>      
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>received
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>>>within a Hello interval + 2 (say) . If not, exit GR.
>>>
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>>>      
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>>It is not clear to me. Do you mean that RTB has the same neighbors as
>>DUT and is on the same network link ?
>>    
>>
>
>Yes.
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>

This is not a solution that you can rely one. For one - you can only use 
it on a BCAST interface where there are
2+ neighbors possible. It will not work for p2p for example.

I prefer a generic solution.

Padma

>
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>>Padma
>>
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>>>This would be faster than using the reacquired Router and Network LSAs to
>>>determine the neighbors, isnt it ?
>>>
>>>Kishore
>>>
>>>
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>>>>        
>>>>
>>>>>Padma.
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>>>For other routers in the network RTA is still reachable and traffic
>>>>>>Will be eventually dropped.
>>>>>>
>>>>>>Kindly correct me,
>>>>>>
>>>>>>Regds,
>>>>>>Ashok/Sujay
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>
>>>      
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