Comments on draft-li-rtgwg-enhanced-ti-lfa

Shraddha Hegde <shraddha@juniper.net> Mon, 07 December 2020 09:18 UTC

From: Shraddha Hegde <shraddha@juniper.net>
To: "draft-li-rtgwg-enhanced-ti-lfa@ietf.org" <draft-li-rtgwg-enhanced-ti-lfa@ietf.org>
CC: "rtgwg@ietf.org" <rtgwg@ietf.org>
Subject: Comments on draft-li-rtgwg-enhanced-ti-lfa
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Authors,

Few comments below.

1. Abstract

TI-LFA backup path computation is always to the destination so it is less likely that a

Node that cannot be bypassed gets skipped due to TI-LFA.

The node that must be visited might get skipped due to node protection procedures that require

Next label lookup. I suggest to update the abstract as below

"
Topology Independent Loop-free Alternate Fast Re-route (TI-LFA) aims
at providing protection of node and adjacency segments within the
Segment Routing (SR) framework. A key aspect of TI-LFA is the FRR
path selection approach establishing protection over the expected
post-convergence paths from the point of local repair.Node protection
procedures for adjacency SIDs and immediate nexthop prefix-sids
require the next label lookup bypassing the immediate node.
The SIDs in the label stack may represent service instructions which
Should not be bypassed. This draft describes a mechanism to advertise
SIDs that cannot be bypassed"

2.Introduction

"traffic engineer" Change to Traffic Engineering"

3.Overview of Enhanced TI-LFA

When the SR-TE path is being built, the node-sids/service sids

Used to build the path MUST use SIDs with no-bypass flag set.

The TI-LFA repair-list building procedure need not change.

It will continue to use SIDs with N bit set.

When the SR-Te label stack is built with "no bypass" SIDs,

The PLR will drop the traffic and not do any node protection procedure for the

The "no-bypass" SIDs

4. Do we really need a "no bypass" flag for adj-sids?

We have the B flag which can be used

5. no-bypass flag in SRH

It is not clear why this is require.

The NB flag in SRV6 SIDs isn't good enough?

Also the NB flag is generally applicable to a specific SID

And should not be a global packet level flag.

Rgds

Shraddha

Juniper Business Use Only

Comments on draft-li-rtgwg-enhanced-ti-lfa Shraddha Hegde
RE: Comments on draft-li-rtgwg-enhanced-ti-lfa Chengli (Cheng Li)