Think about how these things work in SR-MPLS. All of the  “END.D functions” are 
encoded in an MPLS service label (20 bits) or a VNI (24 bits). We merely moved 
those bits into the 32 bit Option Data field of the PPSI.

If it is a good idea in SR-MPLS, why is it a bad idea in SRv6+?


From: Robert Raszuk <>
Sent: Thursday, September 12, 2019 3:34 PM
To: Ron Bonica <>
Cc: EXT - <>; Mark Smith 
<>; Rob Shakir <>; SPRING WG 
<>; 6man <>;; Tarek Saad 
Subject: Re: [spring] Beyond SRv6.

Dear Ron,

I was trying to stop responding but its pretty hard when I see such post like 
your last one ...

> A single IPv6 Option, the PPSI, replaces all of the following SID

Please understand that this is like stating that:

"A single new additional airport replaces all the planes which operate to the 
old airport. "

At most you could say that single new PPSI could contain 2^32 SR functions 
which you call in your draft as "PPSI identifiers"  From your documents it also 
seems that you are defining a service instruction identifier in a flat space 
which can contain the demux for the following technologies:

      o    Layer 2 VPN (L2VPN) 

   o  Layer 3 VPN (L3VPN) 

   o  Virtual Private LAN Service (VPLS) 

   o  Ethernet VPN (EVPN) 

   o  Pseudowires 

It also needs to be observed that putting all of those services into single 
flat table lookup is not a sound design.

But what is most important that common hardware reads just entire header then 
starts processing. So it really makes much more sense to encode SR SIDs and 
related functions and their parameters in the same EH rather then scatter them 

Thank you,


On Thu, Sep 12, 2019 at 8:51 PM Ron Bonica 
<<>> wrote:

Not really. A single IPv6 Option, the PPSI, replaces all of the following SIDs:

  *   END.DX2
  *   END.DX2V
  *   END.DX2U
  *   END.DX2M
  *   END.DT4
  *   END.DX4
  *   END.DT6
  *   END.DX6
  *   END.DT46
  *   END.T


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From: Bernier, Daniel <<>>
Sent: Thursday, September 12, 2019 2:26 PM
To: Ron Bonica <<>>; Mark Smith 
Cc: Rob Shakir <<>>; SPRING WG 
<<>>; 6man 
<<>>; Robert Raszuk 
<<>>;<>; Tarek Saad 
Subject: RE: [spring] Beyond SRv6.

That was precisely my point

Having been involved in pushing SRv6 END behaviours in various targets, I can 
first hand say that the primitives behind SRH processing is quite simple to 
extend. In your extensibility model, every predefined or custom behavior 
becomes a new DOH. On SRH, the EH does not change I just need to inform the 
data plane that when receiving a packet with a specific SID in SRH, do this 
internal processing.

On 2019-09-12, 12:34 PM, "Ron Bonica" 
<<>> wrote:


I think that you may have exposed yet another elephant in the room……

IPv6 defines a robust extensibility architecture, that includes multiple 
extension headers. Initially, IPv6 adoption was slow and router vendors were 
not highly motivated commit extension headers to ASICs. Also, in those days, 
ASICs were not so capable as they are today.

From the above-mentioned data points, we should not infer that it is beyond the 
capability of a modern vendor to develop an ASIC that supports a more complete 
set of extension headers. Two things have changed. As IPv6 adoption progresses, 
vendors are becoming more committed to IPv6. Beyond that, ASICs have become 
more capable over the decades.

We shouldn’t abandon the IPv6 extensibility architecture based on a claim that 
ASICs cannot and will never be able to  process multiple extension headers.


From: ipv6 <<>> On Behalf Of 
Mark Smith
Sent: Thursday, September 12, 2019 1:30 AM
To: EXT -<> 
Cc: Rob Shakir <<>>; SPRING WG 
<<>>; 6man 
<<>>; Robert Raszuk 
<<>>;<>; Tarek Saad 
Subject: Re: [spring] Beyond SRv6.

It's simple because IPv6 doesn't look past the fixed IPv6 header to perform its 
forwarding, and matches on the Destination Address to determine if to perform 
deeper packet host processing.

You're building much more complicated forwarding services if you're going to be 
marching on TLVs etc. past the IPv6 fixed header.

However vendors and carrier engineering groups like selling and deploying new 
gear, so I suppose that's ok. They don't have to operate it or fix it when it 
On Thu, 12 Sep 2019, 13:41 Bernier, Daniel, 
<<>> wrote:


The ability of using a single SRH to convey behaviour information wether they 
are per-segment or per-path has proven to be very simple and quick to define in 
various data plane targets.

At first analysis, trying to replicate with CRH + DOH variants, the logic 
required for service programs is more com​plex.

What happens if I need TLVs mid-point in a path but not at its end (e.g. 
referring to the Ole's ACME analogy) ? Would they now be defined in a 
seg-end-opt or a vpn-dest-opt ? If seg-end-opt then it means non-interested 
midpoint devices will have to lookup beyond the TLVs to get to CRH for next 
segment ?

Similar question would be on how would we implement proxy behaviours either 
dynamic or static ? If I read<;!8WoA6RjC81c!WhasJYFTRmXzKd1g-oMU5hza4EoH-63AFe6qzFFZtlfTRAiabJjCZB0f5dp14y8L$>
 correctly, we then need NSH for richer service chains constructs (think 
Gi-LAN). This means I need CRH, some variants of DOH + NSH​.

I fail to see the simplicity there.

Dan B

From: spring <<>> on 
behalf of<> 
Sent: Wednesday, September 11, 2019 8:57 PM
To: List
Cc: Rob Shakir; 6man; Tarek Saad; Robert Raszuk
Subject: [EXT]Re: [spring] Beyond SRv6.

Hi, folks,
Last year China Telecom begun to implement SRv6 trial in Sichun province for 
the bearing and interconnection of video platforms which are  located in 
different cities, service agilities,secure sepertion, traffic steering and 
other features of SRv6 have been demonstrated in this trial. Based on this, 
SRv6 will be implementated in larger-scale in CT.
No technologies is 100% perfect,I agree that compression mechanism is needed to 
reduce the the overhead of long SID in the long term, but it is better to be 
compatible withe SRH, instead of designing a complete new one. CRH is a 
complete new design, it move the complexities from SRH to DOH.
Moreover, I hope more efforts of SRv6 should be given on how to support new 
services,for instance, Application-aware network (APN). Meanwhile, we should 
consider more on how to implmement smooth transition and protect the network 
assetof carriers.

Best regards

From: Dirk Steinberg<>
Date: 2019-09-09 21:31
To: Gyan Mishra<>
CC: SPRING WG List<>;<>; Robert Raszuk<>; 
Rob Shakir<>; Tarek Saad<>
Subject: Re: [spring] Beyond SRv6.
There seems to be some confusion regarding TI-LFA.
A couple of comments:

- Remote LFA tunnel is not used with SR, only TI-LFA which
  only operates on the node that is the PLR (point of local repair).

- Any encapsulation on the ingress PE with or without EH has nothing
  to do with TI-LFA except for the special case where the ingress PE
  itself is the PLR.

- TI-LFA is not an IGP extension and does not require one.
  It is a purely local computation based on IGP topology.

- The PLR for TI-LFA may need to insert some SIDs into the SID
  list to steer the packet around the failure. For the LFA base case
  no SIDs are needed at all. If SID insertion is needed, the PLR
  will push the required number of labels in the MPLS case.

  For SRv6, the equivalent operation to the label push is to
  insert an EH with the required SID list. The packet will already
  have been encapsulated on the ingress PE and in the most
  common Internet or VPN base use case it will not even have
  an EH so that this EH insertion will result only in a single EH..

  Alternatively, the PLR could also be configured to perform
  encapsulation with a new IPv6 header using the repair SID
  as IPv6 destination address, without needing any EH.
  This will work for the vast majority of cases.
  Remember that one 128-bit SID in SRv6 is in most cases
  equivalent to 2 MPLS labels, i.e. a node label plus an
  adjacency SID can be encoded in a single SRv6 SID.

  Only in extreme cases would the PLR need to add an
  EH to the new IPv6 header with more SIDs.

- EH insertion for TI-LFA has nothing to do with stitching SRv6 domains.

Hope it helps.


Am 08.09.2019 um 09:19 schrieb Gyan Mishra 

>From reading through all the discussion threads the SR insertion is two fold 
>one being for FRR capabilities using Ti-LFA or remote LFA tunnel so end up 
>requiring double EH insertions on the Ingress PE tunnel head end SRv6 source 
>node and then second scenario being a possible EH insertions occurrence on 
>intermediate nodes.  I have not read through the drafts or RFC regarding 
>Ti-LFA with SR but since that is an IGP extension I am guessing an opaque LSA 
>and is not the traditional MPLS FRR link/node/path protection that adds an 
>additional mpls shim so not sure why an EH insertion needs to occur for 
>Ti-LFA.  Can someone clarify that use case for me.  Also the EH insertion on 
>intermediate node what is the use case or reason for that.  My guess is it’s 
>for special use case of stitching SRv6 domains together.  Please clarify..

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