Subject: Re: [sfc] draft-quinn-sfc-nsh: Service Index

From: "Paul Quinn (paulq)" <[email-masked]>
Date: Mon, 2 Mar 2015 15:48:30 +0000

Hi Med,

On Feb 25, 2015, at 10:38 AM, [email-masked]<mailto:[email-masked]> wrote:

Hi Paul,

The current text is clear about the Service Index but is it mandatory to include it in the header? Wouldn’t this information be available locally in the service nodes?

The index in mandatory, it provides several key benefits for the protocol:

1.  Provides simple location within a service path, used for SFF overlay mapping
2.  Provides simple support for cycles (and spirals) with the graph.
3.  Provides, to an administrator, the ability to quickly analyze a packet and know where it is, and where it has been and where its going.
4.  Loop detection within a given path

The text explain that SI allows to detect loops, but isn’t the loop detected too late in the service chain? Wouldn’t be optimal to detect the loop earlier?

If you are asking if the control plane should ensure that a loop isn’t provisioned, sure, in the ideal case but having dataplane detection is very important to ensure packet forwarding isn’t broken.

BTW, what is the behavior when several SFs are embedded in the same node (which information is used to direct the traffic to the appropriate SF)?

The behavior should remain consistent: the SF(s) decrements the index.