I am missing something. In what context is it important to say that
policy 2 is intended to represent the reverse of policy 1?
Yours,
Joel
On 11/12/2021 9:09 PM, Mike Koldychev (mkoldych) wrote:
Hi SPRING WG,
During the PCE session there was a presentation about signaling per-SL
(Segment List) reverse paths, see
https://datatracker.ietf.org/doc/html/draft-ietf-pce-multipath-03#section-4.5
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-multipath-03#section-4.5>.
I received comments to bring this up in the SPRING WG.
In the simplest case, you have two SR Policies in opposite directions,
something like this:
SR policy POL1 <headend = PE1, endpoint = PE2>
Candidate-path CP1
SID-List = <ABC>
SR policy POL2 <headend = PE2, endpoint = PE1>
Candidate-path CP1
SID-List = <CBA>
Where <ABC> and <CBA> are two segment lists that can be considered
“opposites” of each other, maybe traversing the same links in reverse,
or maybe just the same nodes, etc.
However, if the SR Policies have multiple segment lists, it gets more
complicated:
SR policy POL1 <headend = PE1, endpoint = PE2>
Candidate-path CP1
SID-List = <ABC>
SID-List = <DEF>
SR policy POL2 <headend = PE2, endpoint = PE1>
Candidate-path CP1
SID-List = <CBA>
SID-List = <FED>
Where <ABC> and <CBA> are opposites, also <DEF> and <FED> are opposites.
REQ 1: It should be possible to express that multiple reverse SLs
correspond to the same forward SL. For example, if the forward SL is
using Node Segment(s) with ECMP and reverse SLs use Adjacency Segments
to cover multiple ECMP paths in reverse.
REQ 2: It should be possible to express that SL 1 is a reverse of SL 2,
but SL 2 is **not** a reverse of SL 1. I.e., not mutually reverse.
REQ 3: Having a set of reverse SL(s) associated to every forward SL is
useful even if there is no actual SR Policy in the reverse direction.
I.e., if there’s just a unidirectional “forward” SR Policy that needs to
know the return paths for each of its SLs.
Currently SR Policy Architecture does not talk about reverse SLs. I’m
requesting the WG to review the proposal and decide if we should
standardize this.
Thanks,
Mike.
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