Re: [spring] Is srv6 PSP a good idea

[Ron Bonica <[e-mail]>]

Chairs,

Please continue to track this as an open issue.

                                               Ron


Juniper Business Use Only

-----Original Message-----
From: Pablo Camarillo (pcamaril) <[e-mail]> 
Sent: Friday, December 20, 2019 12:36 PM
To: Ron Bonica <[e-mail]>; Joel M. Halpern <[e-mail]>; [e-mail]
Subject: Re: [spring] Is srv6 PSP a good idea

 Hi Ron,

I guess we are making some progress here but going in some circles. So far we have moved from “this violates RFC8200” to “there are no use-cases or benefits” to “this is complex for an ASIC” to “what is the benefit again” and now back to “this is complex for an ASIC”.

As for how easy or not something is, the PSP behavior has been implemented and deployed (running code). The use-cases have been described and positively reinforced by operators. I don't think there is any further explanation to provide.

Happy Holidays,
Pablo.


-----Original Message-----
From: Ron Bonica <[e-mail]>
Date: Tuesday, 17 December 2019 at 16:06
To: "Pablo Camarillo (pcamaril)" <[e-mail]>, "Joel M. Halpern" <[e-mail]>, "[e-mail]" <[e-mail]>
Subject: RE: [spring] Is srv6 PSP a good idea

    Pablo,
    
    In your message below, are you arguing that it is easier for the penultimate node to remove the SRH than it is for the ultimate node to ignore it? I think that would be a stretch.
    
                                                                                  Ron
    
    
    
    Juniper Business Use Only
    
    -----Original Message-----
    From: Pablo Camarillo (pcamaril) <[e-mail]> 
    Sent: Saturday, December 14, 2019 4:50 AM
    To: Ron Bonica <[e-mail]>; Joel M. Halpern <[e-mail]>; [e-mail]
    Subject: Re: [spring] Is srv6 PSP a good idea
    
    Ron,
    
    What is the "price paid by the penultimate segment"? All the current implementations do this at linerate with no performance degradation as I have explained in my email before.
    
    There is substantial benefit. Four operators have deployed PSP, which proves the benefit. 
    It enables new use-cases that have been provided by other members in the list. [1], [2] and [5].
    From operational perspective it is not complex as explained in [3].
    Operators have expressed their value in [4] and [5].
    
    [1].- https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/spring/wTLJQkzC6xwSNPbhB84VH0mLXx0__;!!NEt6yMaO-gk!TzJ8_ZyDvWvLPNwsalQ6RiBzoLkP6Vj30eGaDVFEWdDq_IdPkWwaIL4IcdXeBzk_$ 
    [2].- https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/spring/V0ZpjVLSVZxHaBwecXFxqJjlg_c__;!!NEt6yMaO-gk!TzJ8_ZyDvWvLPNwsalQ6RiBzoLkP6Vj30eGaDVFEWdDq_IdPkWwaIL4IcU9bihBc$ 
    [3].- https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/spring/ssobwemrPz0uEZjvRCZP1e4l_l0__;!!NEt6yMaO-gk!TzJ8_ZyDvWvLPNwsalQ6RiBzoLkP6Vj30eGaDVFEWdDq_IdPkWwaIL4Icc_wo902$ 
    [4].- https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/spring/KXCBHT8Tpy17S5BsJXLBS35yZbk__;!!NEt6yMaO-gk!TzJ8_ZyDvWvLPNwsalQ6RiBzoLkP6Vj30eGaDVFEWdDq_IdPkWwaIL4IcRXo_q-1$ 
    [5].- https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/spring/ErcErN39RIlzkL5SKNVAeEWpnAI__;!!NEt6yMaO-gk!TzJ8_ZyDvWvLPNwsalQ6RiBzoLkP6Vj30eGaDVFEWdDq_IdPkWwaIL4IceGPpSab$ 
    
    Cheers,
    Pablo.
    
    -----Original Message-----
    From: Ron Bonica <[e-mail]>
    Date: Thursday, 12 December 2019 at 21:50
    To: "Pablo Camarillo (pcamaril)" <[e-mail]>, "Joel M. Halpern" <[e-mail]>, "[e-mail]" <[e-mail]>
    Subject: RE: [spring] Is srv6 PSP a good idea
    
        Pablo,
        
        I am not convinced the benefit derived by the ultimate segment justifies the price paid by the penultimate segment. Specifically,
        
        - the ultimate segment benefits because it doesn't have to skip over the SRH with SL == 0
        - in order for the ultimate segment to derive this benefit, the penultimate segment needs to remove bytes from the middle of the packet and update two fields in the IPv6 header
        
        As Joel said, we typically don't add options (i.e., complexity) to a specification unless there is substantial benefit.
        
                                                            Ron
        
        
        
        
        Juniper Business Use Only
        
        -----Original Message-----
        From: spring <[e-mail]> On Behalf Of Pablo Camarillo (pcamaril)
        Sent: Wednesday, December 11, 2019 3:12 PM
        To: Joel M. Halpern <[e-mail]>; [e-mail]
        Subject: Re: [spring] Is srv6 PSP a good idea
        
        Joel,
        
        1.- The use-case for PSP has already been provided at the mailer. There are scenarios where it provides benefits to operators.
        
        2.- The PSP behavior is optional. It is up to the operator in his deployment to decide whether to enable it or not at one particular router.
        Similarly, a vendor may decide not to implement it. The PSP behavior has been implemented by several vendors and deployed (see the srv6 deployment draft).
        
        3.- A network may have PSP enabled at some nodes and not at others.  Everything is still interoperable and works fine.  
        
        4.- PSP is not a complex operation in hardware (doable at linerate on existing merchant silicon). 
        Example: It has been implemented and deployed on Broadcom J/J+. If I recall correctly Broadcom Jericho+ started shipping in March 2016! PSP is supported on this platform at linerate with no performance degradation (neither PPPS nor BW).
        Given that this is doable in a platform from more than 3 years ago, I fail to see how you need "very special provision" to do this.
        
        Is it really something that horrible to provide freedom of choice to the operators deploying?
        
        In summary, it can be implemented without any burden in hardware and deployment experience prove this is beneficial to operators.
        
        Thanks,
        Pablo.
        
        -----Original Message-----
        From: spring <[e-mail]> on behalf of "Joel M. Halpern" <[e-mail]>
        Date: Wednesday, 11 December 2019 at 03:55
        To: "[e-mail]" <[e-mail]>
        Subject: [spring] Is srv6 PSP a good idea
        
            For purposes of this thread, even if you think PSP violates RFC 8200, 
            let us assume that it is legal.
            
            As I understand it, the PSP situation is:
            o the packet arrives at the place (let's not argue about whether SIDs 
            are locators) identified by the SID in the destination address field
            o that SID is the next to last SID in the SID list
            o that sid is marked as / known to be PSP
            o at the intended place in the processing pseudocode, the last (first) 
            entry in the SRH is copied into the destination IPv6 address field of 
            the packet
            -> The SRH being used is then removed from the packet.
            
            In order to evaluate whether this is a good idea, we have to have some 
            idea of the benefit.  It may be that I am missing some of the benefit, 
            and I would appreciate clarification.
            As far as I can tell, the benefit of this removal is that in exchange 
            for this node doing the work of removing the SRH, the final node in the 
            SRH does not have to process the SRH at all, as it has been removed.
            
            I have trouble seeing how that work tradeoff can be beneficial. 
            Removing bytes from the middle of a packet is a complex operation. 
            Doing so in Silicon (we expect this to be done in the fast path of 
            significant forwarders as I understand it) requires very special 
            provision.  Even in software, removing bytes from the middle of a packet 
            requires somewhere between some and a lot of extra work.  It is 
            distinctly NOT free.
            
            In contrast, we have assumed that the work of processing SRH itself is 
            tractable, since otherwise all of SRv6 would be problematic.  So why is 
            this necessary.
            
            Yours,
            Joel
            
            PS: Note that both the MPLS case and the encapsulation case are very 
            different in that the material being removed is at the front of the IP 
            packet.  Pop or prepend are MUCH easier than middle-removal (or 
            middle-insertion).
            
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