Stewart, Andrew and all,
++ Bess WG.
I fully agree that using (targeted) LDP for setup of Martini PWs in an SR-based 
environment is quite problematic for the operators.

One alternative is transition to setup of PWs using MP BGP based on the 
EVPN-VPWS mechanisms (RFC 8214<https://datatracker.ietf.org/doc/html/rfc8214>).

These mechanisms probably require some extension to support PWs that carry 
non-Ethernet customer traffic as well as support of some features that can be 
signaled via LDP for Ethernet PWs but cannot be signaled today with EVPN-VPWS 
(e.g., FCS retention – RFC 4720<https://datatracker.ietf.org/doc/html/rfc4720>).

My guess is that, once the basic EVPN-VPWS signaling is supported, migration of 
LDP-signaled PWs to EVPN-VPWS would be simple enough.

This work, if approved, would require intensive cooperation between PALS WG and 
BESS WG.

My 2c,
Sasha

Office: +972-39266302
Cell:      +972-549266302
Email:   alexander.vainsht...@rbbn.com

From: Pals <pals-boun...@ietf.org> On Behalf Of Stewart Bryant
Sent: Monday, May 30, 2022 11:10 AM
To: Andrew Alston - IETF <andrew-ietf=40liquid.t...@dmarc.ietf.org>; 
p...@ietf.org; mpls-chairs <mpls-cha...@ietf.org>
Cc: SPRING WG <spr...@ietf.org>
Subject: [EXTERNAL] Re: [Pals] [spring] Martini Pseudowires and SR

Including the PALS and MPLS WGs in the discussion.

In the case of PWs, LDP runs directly between the T-PEs to provide the control 
plane. If it is known that the only use of LDP is to support PW, then a 
lightweight profile of LDP might be implemented, ignoring unused parts, but 
this does not necessarily need a standard.

Before you can profile LDP, you have to also profile PWs to determine which 
subset of the PW system you need to support. The danger here is that you end up 
going through the PW development cycle again as old requirements re-emerge.

Stewart



Sent from my iPad


On 30 May 2022, at 07:22, Andrew Alston - IETF 
<andrew-ietf=40liquid.t...@dmarc.ietf.org<mailto:andrew-ietf=40liquid.t...@dmarc.ietf.org>>
 wrote:

Hi All,

Sending this email wearing only the hat of a working group participant.

One of the things that our network uses, and is used by so many networks out 
there, are martini based pseudowires (which for clarity are generally setup 
using what is described in RFC8077).  In an SR world however, this creates a 
problem, because typically you don’t want to run LDP in an SR context.  This 
means that standard martini pseudowires no longer function.  This gets even 
more complicated when you want to do martini based pseudowires over an IPv6 
only network, particularly considering the lack of widespread support for LDP6.

This is also relevant in cases where networks wish to run SR-MPLS in the 
absence of SRv6 for whatever reason.

So, my question to the working group is this:

Is it worth looking at creating a form of LDP light – both compatible with IPv4 
and IPv6 – that simply exists to setup and tear down the service labels for 
point to point services.  A form of targeted LDP without all the other 
complexities involved in LDP – that could potentially run at a lower preference 
than LDP itself (so if LDP is there, use it, if not use this)

Before I start drafting though, I would like to hear from the working group if 
there are others who feel that this is worth doing and, call this a call for 
expressions of interest in those who may be willing to work towards something 
like this.  Happy to take emails on list or off list and see if we can find a 
solution.

Looking forward to hearing from you all

Thanks

Andrew



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