Subject: draft-ietf-6man-segment-routing-header-14 and "local policy"

From: Tom Herbert <[email-masked]>
Date: Sat, 14 Jul 2018 16:12:09 -0700

Hello,

The term "local policy" appears several times in this draft, where
protocol processing of a packet is determined by local policy. I am
trying to figure out how this translates into normative implementation
requirements and an interoperable protocol.

For instance, the draft states:

"Local policy determines when to check for an HMAC and potentially a
requirement on where the HMAC TLV must appear (e.g. first TLV)."

-- and --

"Local policy determines how TLV's are to be processed when the Active
Segment is a local END SID.  The definition of local policy is outside
the scope of this document."

Local policy is not normatively defined and neither are the
requirements specified for which possible policies an implementation
must support. The context of the term makes it seem like the
possibilities in implementation are open ended and potentially allow
proprietary interpretations.

For instance, in the case of HMAC local policy (which I guess would be
set through configuration), the HMAC  could be checked at any time
during processing and local policy might dictate an an arbitrary
ordering of TLVs (extrapolating that if HMAC TLV has a preferred
ordering constraint, new ones in the future might also).

How could this be implemented and be interoperable? Does an
implementation need to allow arbitrary configuration for both the
ordering of TLVs (both in sending and expectations for receiving
them), as well as the order of their processing? If the requirements
are something less than this such that implementations can restrict
possible policies, then how can interoperability be achieved if there
is a mismatch between what two implementations choose to do? For
example, what if one implementation implements the a policy to send
TLV A and then TLV B, but another one wants to receive TLV B before
TLV A?

Tom

---

From: "Darren Dukes (ddukes)" <[email-masked]>
Date: Tue, 17 Jul 2018 13:27:38 +0000

Hi Tom, I think you have raised a good point.  This area can be tackled this with a data model defined in the Management section that I talked about yesterday in the 6man presentation.

Defining a data model for SIDs at endpoint and SRH at source nodes will tell us what can be controlled in any implementation.
 
Darren 

On 2018-07-14, 7:12 PM, "ipv6 on behalf of Tom Herbert" <[email-masked] on behalf of [email-masked]> wrote:

    Hello,

    
    
    -- and --

    

    Tom
    
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