I think you’re confusing the symmetry a stateful SF requires and symmetric
chain. We can still create symmetric chains even if every SF in these chains is
stateless. So I think Tim’s proposal is ok, you can mark a SF stateful by other
property such as “stateful”, using “symmetric” here will make people confused.
You can let SFC consider this when your chain includes such a stateful SF and
create RSP. Let me make an example.
SF1 --------------> SF2------------------->SF3
(stateless) (stateful) (stateless)
For such RSP, reverse RSP must include this SF2 because it is stateful.
SF4-------------->SF2--------------------->SF5
(stateless) (stateful) (stateless)
You can refer to https://tools.ietf.org/html/rfc7665 and extend it if it didn’t
consider your use case ☺
From: Brady Allen Johnson [mailto:[email protected]]
Sent: Thursday, November 10, 2016 8:47 PM
To: Swati Deshpande <[email protected]>; Yang, Yi Y
<[email protected]>
Cc: Diego Jesus Granados Lopez <[email protected]>;
[email protected]; Tim Rozet <[email protected]>
Subject: Re: [sfc-dev] Deprecating SFC, SFP, and RSP symmetric fields
I agree.
You have to ask the question:
Why would a Service Chain be symmetric?
Answer:
Because one or several Service Functions in that chain need both uplink and
downlink packets.
So, as Swati mentioned, instead of putting the burden on the Operator to know
about the Service Functions, configure the symmetric property on the Service
Function, and let SFC create the reverse/symmetric Service Chain internally
when needed.
This change simplifies the SFC configuration.
Regards,
Brady
On 10/11/16 13:34, Swati Deshpande wrote:
As an Abstract object , SF can be in symmetric SFC or asymmetric SFC.
If we think of use cases, there is one category of SFs, that can function only
when set up in symmetric SFC, and second category of SF that can function in
both symmetric as well as asymmetric SFC.
So the real question is "Do we put onus on operator to know about category of
SFs being deployed and set up SFC accordingly? Or
do we derive symmetric nature of SFC based on category of SF being deployed in
the chain.
If we want to make life easy for operators and also give them control, by
default symmetric nature of SFC can be derived from SF category and additional
control can be added on SFC to override the default behavior.
Regards,
Swati
On Thu, Nov 10, 2016 at 5:28 PM, Yang, Yi Y
<[email protected]<mailto:[email protected]>> wrote:
But a SF can be in symmetric chain, it also can be in asymmetric chain,
symmetric or asymmetric is for chain or path, not for SF. It is really weird a
bit if you say a SF is symmetric or asymmetric.
From: Swati Deshpande
[mailto:[email protected]<mailto:[email protected]>]
Sent: Thursday, November 10, 2016 7:45 PM
To: Diego Jesus Granados Lopez
<[email protected]<mailto:[email protected]>>
Cc: Yang, Yi Y <[email protected]<mailto:[email protected]>>; Brady Allen
Johnson
<[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>
Subject: Re: [sfc-dev] Deprecating SFC, SFP, and RSP symmetric fields
Agree with Diego, Symmetric nature of SFC should be determined based on type of
SF used in the chain.
SF types dpi, firewall , NAT, need to see both forward and reverse flows hence
SFC built using such SFs would need to be symmetric.
If any one SF in a SFC has symmetric path requirement, RSP should be symmetric.
Regards,
Swati
On Thu, Nov 10, 2016 at 4:59 PM, Diego Jesus Granados Lopez
<[email protected]<mailto:[email protected]>>
wrote:
Hi,
Not really following your point on this. I think the contrary: SF having a
symmetric flag makes all the sense, but it would be desirable that SFP don't
have it. E.g. think of the header enrichment service function type: it would
be great if any HE vendor could specify whether his HE SF is symmetric or not
(e.g. Ericsson sells the "Ericsson HE"; it is a transparent HE SF that don't
need symmetry, hence it is a not-symmetric SF"; another vendor sells the
"OtherVendor HE", that is a proxy, and defines its SF as symmetric). From the
SFC operator standpoint, he simply choses a HE SF among all the vendors
building SFs belonging to the header enrichment type and defines the path, and
it is SFC what determines whether the symmetric RSP is needed or not depending
on the SFs part of it. This way, we simplify operation (i.e. the operator
choses a HE based on business needs, but never needs to think about symmetry)
and prevent configuration mistakes (e.g. the operator configuring a SFP
as not symmetric but including a SF which needed the symmetric path). I could
think of the same reasoning being applicable for other SF types: dpi...
Best regards,
Diego
-----Original Message-----
From:
[email protected]<mailto:[email protected]>
[mailto:[email protected]<mailto:[email protected]>]
On Behalf Of Yang, Yi Y
Sent: jueves, 10 de noviembre de 2016 12:06
To: Brady Allen Johnson
<[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>
Subject: Re: [sfc-dev] Deprecating SFC, SFP, and RSP symmetric fields
I think SFP can keep it, others can remove it, it doesn't make sense for a SF
to have a symmetric flag.
-----Original Message-----
From:
[email protected]<mailto:[email protected]>
[mailto:[email protected]<mailto:[email protected]>]
On Behalf Of Brady Allen Johnson
Sent: Thursday, November 10, 2016 6:42 PM
To: [email protected]<mailto:[email protected]>
Subject: [sfc-dev] Deprecating SFC, SFP, and RSP symmetric fields
Currently there is a symmetric field in the SFC, SFP, and RSP data models. I
will deprecate these fields now in Carbon.
Instead of defining this in one of [SFC, SFP, RSP] a chain will be symmetric if
it has an SF whose SF-type has the symmetry flag set to true. The SF-type
symmetry field was also added in Beryllium.
It was always confusing what it meant if there is some combination of symmetric
values for the SFC, SFP, and RSP. That is, what if SFC:symmetric is true,
SFP:symmetric is false, and RSP:symmetric is true? Or some similar combination?
Currently, a reverse RSP is created if the SFP symmetric field is true.
This will still be the case in Carbon, but we will also check the SF-types as
explained above. In Nitrogen, we'll remove the SFP symmetric field check.
I've already updated the SFC Carbon Release Plan to mention these deprecated
fields.
Regards,
Brady
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