Re: [spring] WG Adoption Call for draft-dong-spring-sr-for-enhanced-vpn

"Joel M. Halpern" <> Tue, 02 February 2021 19:54 UTC

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To: Colby Barth <>, "" <>
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From: "Joel M. Halpern" <>
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Date: Tue, 2 Feb 2021 14:54:02 -0500
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Subject: Re: [spring] WG Adoption Call for draft-dong-spring-sr-for-enhanced-vpn
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Colby, you are, as far as I can tell, correct that the potential for 
state explosion is extremely risky and requires careful management. 
That is why the bestbar draft emphasis that the state is abotu slice 
aggregates, not end-to-end slices, and probably not even individual IETF 
network slices.


On 2/2/2021 2:19 PM, Colby Barth wrote:
> Tarek, indeed …
> draft-bestbar-spring-scalable-ns-00 provides a relevant example of the rather enormous amount of state the solution described in draft-dong-spring-sr-for-enhanced-vpn results in:
>     "Notably, this approach requires maintaining per slice state for each
>     topological element on every router in the network in both the
>     control and data plane.  For example, a network composed of 'N'
>     nodes, where each node has up to 'K' adjacencies to its neighbors, a
>     node would have to assign and advertise 'M' Slice Prefix-SIDs and 'M'
>     Slice Adjacency-SID(s) to each of it 'K' adjacencies.  Consequently,
>     a router will have to maintain up to (N+K)*M SIDs in the control
>     plane, and an equal number of label routes in its forwarding plane."
> Put in practical terms, this implicitly limits the number of VTNs or, in draft-bestbar-teas-ns-packet-01 terminology, the number of Slice aggregates that can be offered.  It also introduces a dependency between the network size and the number of VTNs.  i.e. the larger the network, the smaller the number of VTNs that can be supported.
> —Colby
>> On Feb 2, 2021, at 12:54 PM, Tarek Saad <> wrote:
>> Hi Eduard,
>> Inline..
>> On 2/2/21, 10:50 AM, "spring on behalf of Vasilenko Eduard" < on behalf of> wrote:
>> Hi all,
>> There is the general trend to encode the action into the packet, not to distribute states in the control plane for all possible traffic types. Granularity, programmability are better.
>> [TS]: Indeed, we are in agreement on encoding the information in packet as opposed to distributing states in the control plane. In draft-bestbar-spring-scalable-ns, a separate ID inside the packet is proposed to carry the needed information. However, this draft <draft-dong-spring-sr-for-enhanced-vpn> is proposing distributing per VTN state in the network which is completely against your argument ...
>> Regards,
>> Tarek
>> This type of virtualization is fully in-line with this trend.
>> Support.
>> Eduard
>> From: spring [] On Behalf Of James Guichard
>> Sent: Wednesday, January 27, 2021 12:47 PM
>> To:
>> Cc:
>> Subject: [spring] WG Adoption Call for draft-dong-spring-sr-for-enhanced-vpn
>> Dear WG:
>> This message starts a 2 week WG adoption call for ending February 10th 2021.
>> After review of the document please indicate support (or not) for WG adoption to the mailing list and if you are willing to work on the document, please state this explicitly. This gives the chairs an indication of the energy level of people in the working group willing to work on this document. Please also provide comments/reasons for your support (or lack thereof) as this is a stronger way to indicate your (non) support as this is not a vote.
>> Thanks!
>> Jim, Bruno & Joel
>> Juniper Business Use Only
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>> spring mailing list