Re: [spring] WG adoption requested for draft-filsfils-spring-sr-recursing-info

Hi Deccan,

> On Aug 23, 2016, at 4:39 AM, peng.shaofu@zte.com.cn wrote:
> 
> Hi Stefano 
> 
> Sure, SRRI provided in this document can explicitly indicate a recursive operation (or relationship). 
> But it maybe a default behavior to do recursive operation when an SR-NODE received remote prefix-sid with L/V flag set according to the documents already existed. For example, 
> prefix reachability advertisement received: 
>     prefix (1.0.0.99/32) 
>         prefix-sid (30004), L/V flag set,  //ISIS-SR 
>         "IPv4 Source Router ID" is 1.0.0.4 //rfc7794 
> Then, prefix 1.0.0.9/32 can do recursion to prefix 1.0.0.4/32 by default.

there are other cases where V/L are used so I wouldn’t 
bind these flags to the recursive behavior.

> If "default behavior" is not accepted, we can define a new RECURSIVE flag in Prefix-SID Sub-TLV. 

if I understand your proposal, you could:
. attach the SourceRouterID (RFC7794) to the prefix
. attach a prefix-sid with:
   . recursive flag set, which means the sid is to be 
      taken from the sourceRouterID
   . optionally set the V/L flag and also a local label
   . if no V/L flag are set, the value of the sid/label 
      field in the prefix-sid must be 0 on transmit and 
      ignored on receive.

I see at least 2 problems with that:
1. the value of the prefix-sid you’re going to advertise 
   will be misinterpreted by non-srri-capable nodes 
   (i.e.: nodes know knowing the recursive flag). I.e: The 
   value of the prefix sid would be either an explicit 
   null label either a 0-value index.
2. RFC7794 states that: the Router ID advertised is 
   always the Router ID of the IS-IS instance that 
   originated the advertisement.

   This reduces the ability to use other addresses of the 
   node for recursion.

Bottom line, having a separate repository for the recursing 
information is the safest and cleanest option which allows 
better flexibility (i.e.: allowing to recurse to a 
non-router-ID address) and which ensure backward 
compatibility (i.e.: non-srri-nodes will simply ignore the 
whole srri info and consider the prefix as it had no sid at 
all).

> BTW, all we discussed is SID recursive but not sharing,

of course it is sharing. As defined in the draft, the 
local label attached to the srri info it’s an optional 
optimization. Without the local label, you will share the 
same sid among multiple prefixes. 

> even the first case in this draft is actually not SID sharing, otherwise it will be cared by draft-ietf-spring-conflict-resolution. 

No, it is not a conflict. Having a dedicated srri 
repository makes it clear.

s.

> Thanks 
> Deccan 
> 
> 
> 
> 
> 
> "Stefano Previdi (sprevidi)" <sprevidi@cisco.com>
> 2016-08-22 21:38
> 
> 收件人
> "peng.shaofu@zte.com.cn" <peng.shaofu@zte.com.cn>,
> 抄送
> SPRING WG <spring@ietf.org>
> 主题
> Re: [spring] WG adoption requested for draft-filsfils-spring-sr-recursing-info
> 
> 
> 
> 
> 
> 
> > On Aug 9, 2016, at 5:55 AM, peng.shaofu@zte.com.cn wrote:
> > 
> > Other documents have already addressed this issue,
> 
> 
> I don’t think so. Can you point to these documents ?
> 
> 
> > for example, set L-flag of Prefix-SID Sub-TLV in draft-ietf-isis-segment-routing-extensions-05 and contain IPv4 Source Router ID in rfc7794. 
> 
> 
> the L flag has the solely purpose of indicating the sid contains a local value. Typically it goes with the V flag that indicates a value (i.e.: local label).
> 
> Nothing is mentioned regarding sharing the same sid among different services.
> 
> s.
> 
> 
> 
> > 
> > 
> > Thanks, 
> > 
> > Deccan 
> > 
> > 
> > 
> > 
> > 
> > [spring] WG adoption requested for draft-filsfils-spring-sr-recursing-info 
> > "John G. Scudder" <jgs@juniper.net> Sun, 24 July 2016 12:54 UTCShow header
> > Dear WG,
> > 
> > As we discussed at our meeting, working group adoption has been requested for draft-filsfils-spring-sr-recursing-info. Please reply to the list with your comments, including although not limited to whether or not you support adoption. Non-authors are especially encouraged to comment.
> > 
> > We will end the call on August 31, 2015. 
> > 
> > Authors, please indicate whether you are aware of any relevant IPR and if so, whether it has been disclosed.
> > 
> > Thanks,
> > 
> > --Bruno and John
> > 
> > 
> > _______________________________________________
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> > spring@ietf.org
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> > 
> 
> 