Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions

Peter Psenak <ppsenak@cisco.com> Mon, 29 December 2014 11:05 UTC

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Date: Mon, 29 Dec 2014 12:04:53 +0100
From: Peter Psenak <ppsenak@cisco.com>
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To: Shraddha Hegde <shraddha@juniper.net>, "draft-ietf-ospf-segment-routing-extensions@tools.ietf.org" <draft-ietf-ospf-segment-routing-extensions@tools.ietf.org>, "draft-ietf-isis-segment-routing-extensions@tools.ietf.org" <draft-ietf-isis-segment-routing-extensions@tools.ietf.org>
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Subject: Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions
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Shraddha,

On 12/29/14 10:06 , Shraddha Hegde wrote:
> Peter,
>
> The requirement here is to get an un-protected path for services which do not want to divert the traffic on protected path in any case.

can you give an example of such a service and a reasoning why such 
service would want to avoid local protection along the path?

thanks,
Peter

> So when the originator of node-sid signals un-protected path requirement, there is always an unprotected path.
>
> Regarding the protected path, it is the default behavior as it exists today. You get protection if it's available otherwise you don't get protection.
>
> In fact, you can have the new flag to say "NP flag" meaning non-protected flag which can be set for the unprotected path.
> By default it remains off and gives the behavior as it exists today.
>
>
> Rgds
> Shraddha
>
> -----Original Message-----
> From: Peter Psenak [mailto:ppsenak@cisco.com]
> Sent: Monday, December 29, 2014 2:26 PM
> To: Shraddha Hegde; draft-ietf-ospf-segment-routing-extensions@tools.ietf.org; draft-ietf-isis-segment-routing-extensions@tools.ietf.org
> Cc: ospf@ietf.org; isis-wg@ietf.org
> Subject: Re: [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions
>
> Shraddha,
>
> I do not see how an originator of the node-sid can mandate a protection for the prefix on other routers. What if there is no backup available on a certain node along the path?
>
> The parallel with the B-flag in adj-sids is not right - in case of adj-sid the originator has the knowledge about the local adjacency protection and as such can signal it it it's LSA.
>
> thanks,
> Peter
>
>
> On 12/29/14 09:47 , Shraddha Hegde wrote:
>> Peter,
>>
>>
>> Pls see inline.
>>
>> Rgds
>> Shraddha
>>
>> -----Original Message-----
>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>> Sent: Monday, December 29, 2014 2:02 PM
>> To: Shraddha Hegde;
>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> Subject: Re: [Isis-wg] Mail regarding
>> draft-ietf-ospf-segment-routing-extensions
>>
>> Shraddha,
>>
>> I do not see how an originator can set any flag regarding the protection of the locally attached prefix.
>> <Shraddha> The originator advertises 2 node-sids. One with p flag set and the other without the p-flag set.
>>
>>    It's all the routers on the path towards such prefix that need to deal with the protection.
>> <Shraddha> The receiving nodes will download protected path for the
>> node-sid with p-flag set and download Unprotected path for the node-sid with p-flag unset.
>>
>> Signaling anything from the originator seems useless.
>> <Shraddha>  For node-sids it's the others who need to build the forwarding plane but it's only the originator who can signal which of
>>                           Sid need to be built with protection and which not. Other routers on the path cannot signal this information.
>
>
>
>>
>> With this you have two paths for the node. One is protected and the other is unprotected. This meets the requirement of having an un-protected path.
>>
>> It's very much in parallel to B-flag in adj-sids. It is similar to
>> advertising multiple adj-sids one with B-flag on and other with b-flag off , to get protected and unprotected Adj-sids.
>>
>> thanks,
>> Peter
>>
>> On 12/29/14 09:26 , Shraddha Hegde wrote:
>>> Yes.You are right.
>>>
>>> Lets say a prefix sid has a flag "p flag". If this is on it means build a path and provide protection.
>>> If this is off it means build a path with no protection.
>>> The receivers of the prefix-sid will build forwarding plane based on this flag.
>>>
>>> The applications building the paths will either use prefix-sids with p flag on or off based on the need of the service.
>>> Rgds
>>> Shraddha
>>>
>>>
>>> -----Original Message-----
>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>>> Sent: Monday, December 29, 2014 1:49 PM
>>> To: Shraddha Hegde;
>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>>> Subject: Re: [Isis-wg] Mail regarding
>>> draft-ietf-ospf-segment-routing-extensions
>>>
>>> Shraddha,
>>>
>>> the problem is that the node that is advertising the node-sid can not advertise any data regarding the protection of such prefix, because the prefix is locally attached.
>>>
>>> thanks,
>>> Peter
>>>
>>> On 12/29/14 09:15 , Shraddha Hegde wrote:
>>>> Peter,
>>>>
>>>> If there is a service which has to use un-protected path and while
>>>> building such a path if the node-sids Need to be used (one reason
>>>> could be label stack compression) , then there has to be unprotected node-sid that this service can make use of.
>>>>
>>>> Prefix -sids could also be used to represent different service
>>>> endpoints which makes it even more relevant to have A means of representing  unprotected paths.
>>>>
>>>> Would be good to hear from others on this, especially operators.
>>>>
>>>> Rgds
>>>> Shraddha
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>>>> Sent: Monday, December 29, 2014 1:35 PM
>>>> To: Shraddha Hegde;
>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>>>> Subject: Re: [Isis-wg] Mail regarding
>>>> draft-ietf-ospf-segment-routing-extensions
>>>>
>>>> Shraddha,
>>>>
>>>> node-SID is advertised by the router for the prefix that is directly attached to it. Protection for such local prefix does not mean much.
>>>>
>>>> thanks,
>>>> Peter
>>>>
>>>> On 12/24/14 11:57 , Shraddha Hegde wrote:
>>>>> Authors,
>>>>> We have a "backup flag" in adjacency sid to indicate whether the
>>>>> label is protected or not.
>>>>> Similarly. I think we need a flag in prefix-sid as well to indicate
>>>>> whether the node-sid is to be protected or not.
>>>>> Any thoughts on this?
>>>>> Rgds
>>>>> Shraddha
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Isis-wg mailing list
>>>>> Isis-wg@ietf.org
>>>>> https://www.ietf.org/mailman/listinfo/isis-wg
>>>>>
>>>>
>>>> .
>>>>
>>>
>>> .
>>>
>>
>> .
>>
>
> .
>