Peter, Shraddha,
Primarily — I don’t think that use of the ‘B’ flag in the Adj-SID implies that
there MUST be a backup route installed, it merely indicates that the Adj-SID
MAY be subject to re-routing (and hence strict placement on an adjacency may
not be honoured during link failures).
For me, I’m unclear on what the practical use of not requesting backup for a
{Node,Prefix}-SID could be — its very nature (“the shortest path to X” where X
is a node/prefix) means that it is not well defined in terms of a route through
the network, and hence is not well defined in terms of performance. This (to
me) says that we cannot really rely on such a SID for performance-sensitive
traffic, and hence must always be able to tolerate events such as FRR paths
during protection.
The fact that AdjSID maps deterministically to a particular link, about which
the calculating entity (PCE/iLER) can know details of, means that performance
can be inferred - and hence strict affinity to that path (and/or failure when
it is not available) is of utility.
Kind regards,
r.
> On 29 Dec 2014, at 08:56, Peter Psenak <[email protected]> wrote:
>
> 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:[email protected]]
>> Sent: Monday, December 29, 2014 2:02 PM
>> To: Shraddha Hegde;
>> [email protected];
>> [email protected]
>> Cc: [email protected]; [email protected]
>> 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:[email protected]]
>>> Sent: Monday, December 29, 2014 1:49 PM
>>> To: Shraddha Hegde;
>>> [email protected];
>>> [email protected]
>>> Cc: [email protected]; [email protected]
>>> 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:[email protected]]
>>>> Sent: Monday, December 29, 2014 1:35 PM
>>>> To: Shraddha Hegde;
>>>> [email protected];
>>>> [email protected]
>>>> Cc: [email protected]; [email protected]
>>>> 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
>>>>> [email protected]
>>>>> https://www.ietf.org/mailman/listinfo/isis-wg
>>>>>
>>>>
>>>> .
>>>>
>>>
>>> .
>>>
>>
>> .
>>
>
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