Re: [OSPF] draft-ietf-ospf-segment-routing-extensions-03

[Peter Psenak <[e-mail]>]

Hi Shraddha,

please see inline:

On 12/16/14 18:31 , Shraddha Hegde wrote:
> Rob,
>
> Pls see inline..
>
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]]
> Sent: Tuesday, December 16, 2014 10:11 PM
> To: Shraddha Hegde; [e-mail]; [e-mail]
> Cc: [e-mail]
> Subject: Re: draft-ietf-ospf-segment-routing-extensions-03
>
> Shraddha,
>
> Is it really up to the neighbor to specify what was previously a bundle?
>
> <Shraddha>  The graceful restart in OSPF as per RFC  3623 works by learning  the LSAs from neighbor after the restating router comes up and builds the LSA database based on the learnt 		LSAs.
> 	          The neighbor relays back the LSA generated by the restarting router. The Extended link LSA contains the adj-sid Label TLV which
>                             Has the "s bit" set indicating the label is a set label. If there are multiple such set labels associated with a link, its difficult to associate which label was allocated for which bundle.
>
>                            If there is a some kind of identifier for the bundle, the label can be easily associated.

I don't think adding additional info to be distributed by the protocol 
is the right way to address the local data persistence across 
restart/switch over. If you need to make sure that the LSA contains the 
same data prior and after GR, you can checkpoint them and restore from 
checkpoint after GR.

>
>
> It is surely the local configuration of the node that determines what the bundle is in the first place, and this is persistent over a graceful-restart of the session?
>
> <Shraddha> Yes, IMO local configuration decides which links belong to the bundle. This configuration is persistent over graceful restart.
>                            You MAY want to bundle all the parallel links between two nodes into a bundle, in which case the existing protocol operations work fine.
>                             But I think protocol should provide flexibility to make multiple bundles, able to assign a link to multiple bundles (if so desired) and recovering the label across restart.

sure. If you need to make sure that same label is used prior and post 
GR, you do not need protocol help for that.

thanks,
Peter
>
>
> Thanks,
> r.
>
> [16/12/2014 16:34, "Shraddha Hegde" <[e-mail]>]
>
>> Peter,
>>
>> An extended link LSA can contain multiple adj-sid labels with "s bit" set.
>> During graceful restart , when self generated LSAs are learnt from
>> neighbors, A handle is required to associate the set label with the
>> bundle.
>>
>> I think a group-id field along with set label would serve the purpose.
>>
>> Rgds
>> Shraddha
>> -----Original Message-----
>> From: Peter Psenak [mailto:[e-mail]]
>> Sent: Sunday, December 14, 2014 4:08 PM
>> To: Shraddha Hegde;
>> [e-mail]
>> Cc: OSPF WG List
>> Subject: Re: draft-ietf-ospf-segment-routing-extensions-03
>>
>> Shraddha,
>>
>> the idea is that you can assign the same Adj-SID to multiple links.
>> That way you can create multiple sets as you need.
>>
>> thanks,
>> Peter
>>
>>
>> On 12/13/14 19:19 , Shraddha Hegde wrote:
>>> Authors,
>>>
>>>           When there are multiple parallel links between two nodes, it
>>> is useful to
>>>
>>> Group them into different bundles and use each bundle for load-balancing
>>>    for different traffic flows.
>>>
>>> What we have in adjacency sid is just a flag to indicate that the
>>> label is a "set label" by setting a flag
>>>
>>> In adj-sid TLV. It serves the purpose when all the parallel links
>>> are in one bundle but not sufficient when
>>>
>>> There can be different bundles and different labels for each of them.
>>>
>>> An identifier for the group, probably "group-id" is needed to
>>> associate the label with the interface group.
>>>
>>> Any thoughts on this?
>>>
>>> Rgds
>>>
>>> Shraddha
>>>
>>
>
> .
>