Re: Exit-Graceful Restart Condition

Padma Pillay-Esnault <ppe@CISCO.COM> Tue, 31 May 2005 22:39 UTC

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Date: Tue, 31 May 2005 15:40:04 -0700
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From: Padma Pillay-Esnault <ppe@CISCO.COM>
Subject: Re: Exit-Graceful Restart Condition
To: OSPF@PEACH.EASE.LSOFT.COM
In-Reply-To: <429CE51E.8010909@cisco.com>
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Acee Lindem wrote:

> sujay wrote:
>
>> Hi Padma,
>>
>> Guess we *must* run the dead interval timer on a per neighbor basis,
>>  
>>
> Hi Sujay,
>
> IMHO, this is the norm rather than the exception.
>

Agree - this is usual behavior.

Padma

>> else
>> for the maximum configured dead interval amongst all possible
>> neighbours.
>> It could be of course implementation specific.
>>
>> Solves more than the one issue mentioned in this thread !
>>
>> Regds,
>> Sujay
>>
>> -----Original Message-----
>> From: Mailing List [mailto:OSPF@PEACH.EASE.LSOFT.COM] On Behalf Of Padma
>> Pillay-Esnault
>> Sent: Friday, May 27, 2005 8:40 PM
>> To: OSPF@PEACH.EASE.LSOFT.COM
>> Subject: Re: Exit-Graceful Restart Condition
>>
>>
>> Kishore Rao wrote:
>>
>>  
>>
>>> ----- Original Message -----
>>> From: "Padma Pillay-Esnault" <ppe@cisco.com>
>>> To: <OSPF@peach.ease.lsoft.com>
>>> Sent: Wednesday, May 25, 2005 11:54 AM
>>> Subject: Re: Exit-Graceful Restart Condition
>>>
>>>
>>>
>>>
>>>   
>>>
>>>> Kishore Rao wrote:
>>>>
>>>>  
>>>>     
>>>>
>>>>> ----- Original Message -----
>>>>> From: "Acee Lindem" <acee@cisco.com>
>>>>> To: <OSPF@peach.ease.lsoft.com>
>>>>> Sent: Wednesday, May 25, 2005 10:10 AM
>>>>> Subject: Re: Exit-Graceful Restart Condition
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>    
>>>>>       
>>>>>
>>>>>> 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
>>>>>    
>>>>>       
>>>>
>>> received
>>>
>>>
>>>   
>>>
>>>>> within a Hello interval + 2 (say) . If not, exit GR.
>>>>>
>>>>>
>>>>>    
>>>>>       
>>>>
>>>> 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.
>>>
>>>
>>>   
>>
>>
>> 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
>>
>>  
>>
>>>
>>>
>>>   
>>>
>>>> Padma
>>>>
>>>>  
>>>>     
>>>>
>>>>> This would be faster than using the reacquired Router and Network 
>>>>> LSAs to determine the neighbors, isnt it ?
>>>>>
>>>>> Kishore
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>    
>>>>>       
>>>>>
>>>>>>      
>>>>>>         
>>>>>>
>>>>>>> Padma.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>        
>>>>>>>           
>>>>>>>
>>>>>>>> For other routers in the network RTA is still reachable and 
>>>>>>>> traffic Will be eventually dropped.
>>>>>>>>
>>>>>>>> Kindly correct me,
>>>>>>>>
>>>>>>>> Regds,
>>>>>>>> Ashok/Sujay
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>          
>>>>>>>>             
>>>>>>>
>>>>>    
>>>>>       
>>>>
>>>
>>>
>>>   
>>
>>
>>  
>>
>