Subject: PW to PSN mapping (again)

From: "Paul Doolan" <[email-masked]>
Date: Wed, 6 Oct 2004 16:44:58 -0400

Hello,

It's been a while since I've been active in this area but the fascinating RSVP-TE thread makes it seem like I never left. Didn't we see the RSVP vs LDP movie already? Still it's nice to see that some of the original combatants are around to clarify the record. Today however I have no questions about RSVP.

I would be grateful if any of you can shed some light on a thing that's been puzzling me for a little while. Back in August there was a little thread "[PWE3] PW to PSN tunnel mapping" started by Benny Lønstrup Ammitzbøll. He asked how a PE might know to which PSN tunnel a PW belongs. Before that thread morphed into the QoS one there was an uchallenged contribution that said it was a matter of local policy at the PE which decided this mapping. 

Matters of local policy tend to create interoperability problems. In particular this one (if true) might be better stated as "it's a matter of local policy at the ingress (to which PSN tunnel a PW is mapped)". And the corollary is surely that the egress is SOL in the 'local policy' department. Perhaps more accurately the egress's policy options are binary. It can take pseudowire traffic as and from whence it arrives or it can drop it.

Is it really the case that I can open up multiple tunnels to an egress PE and fire off pseudowire traffic down whichever of them I choose and everything will work fine? Or does this depend not only on the local policy of the ingress but also on the vendor implementation at the egress? 

Paul

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From: "Shah, Himanshu" <[email-masked]>
Date: Thu, 7 Oct 2004 09:07:41 -0400

The service guarentees sold on ACs pretty much dictates what kind of
transport tunnels the PW will ride on. You can then, 
1) either build TE tunnels accordingly and do CAC as you map
      PWs (of same characteristics) over it.  You can apply thresholds that
      would dictate up or downsizing of tunnel b/w dynamically
2) do BE tunnels
3) manually map PWs over preconfigured suitable transport tunnels.
 
One of the thing an ingress PE may want to take into consideration is AC characteristics
of Egress PE when selecting a transport tunnel from ingress to egress and for
applying appropriate traffic policing/shaping at ingress (to avoid packet drops at egress). 
 For this you may want to look at draft-shah-PWE3-pw-qos-signalling-00.txt. (peddling my draft..:-)
 
/himanshu

-----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Wednesday, October 06, 2004 4:45 PM
To: [email-masked]
Subject: [PWE3] PW to PSN mapping (again)

Hello,

It’s been a while since I’ve been active in this area but the fascinating RSVP-TE thread makes it seem like I never left. Didn’t we see the RSVP vs LDP movie already? Still it’s nice to see that some of the original combatants are around to clarify the record. Today however I have no questions about RSVP.

I would be grateful if any of you can shed some light on a thing that’s been puzzling me for a little while. Back in August there was a little thread “[PWE3] PW to PSN tunnel mapping” started by Benny Lønstrup Ammitzbøll. He asked how a PE might know to which PSN tunnel a PW belongs. Before that thread morphed into the QoS one there was an uchallenged contribution that said it was a matter of local policy at the PE which decided this mapping. 

Matters of local policy tend to create interoperability problems. In particular this one (if true) might be better stated as “it’s a matter of local policy at the ingress (to which PSN tunnel a PW is mapped)”. And the corollary is surely that the egress is SOL in the ‘local policy’ department. Perhaps more accurately the egress’s policy options are binary. It can take pseudowire traffic as and from whence it arrives or it can drop it.

 

Paul

  _____

---

From: "Paul Doolan" <[email-masked]>
Date: Thu, 7 Oct 2004 10:42:14 -0400

Himanshu,

1,2 and 3 though are operations that occur at the ingress. I'm still puzzled as to how the egress knows (given any of these tunnel setup methods) over which tunnel a particular pseudowire's datastream is going to appear. My concern is unambiguously identifying such a, newly appearing, stream. I can believe that this is possible if the label value signaled (by the egress in this case) is unique for the platform. What I'm not aware of is any statement that _requires_ this to be true. In draft-ietf-pwe3-control-protocol-10.txt the label is signaled as a "Generic Label". Does anyone know if there are semantics associated with that type of label or its use that require it to be unique? 

And I'll take a look at your draft....

thanks

Pd 

-----Original Message-----
From: Shah, Himanshu [mailto:[email-masked]] 
Sent: Thursday, October 07, 2004 9:08 AM
To: Paul Doolan; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

2) do BE tunnels

/himanshu

	-----Original Message-----
	From: Paul Doolan [mailto:[email-masked]]
	Sent: Wednesday, October 06, 2004 4:45 PM
	To: [email-masked]
	Subject: [PWE3] PW to PSN mapping (again)

	Hello,

	 

	Paul

  _____

---

From: "Shah, Himanshu" <[email-masked]>
Date: Thu, 7 Oct 2004 10:59:09 -0400

In most common cases for PWs, PHP is used (and hence per-platform label for PW).
In which case, association to an incoming tunnel is lost. This is good in the sense
that FRR or any other mechanism is not constrained to what incoming interface
an egress PE will get the PW traffic.
 
May I ask why do you think it is necessary for egress PE to know on which tunnel
a particular PW traffic would arrive? The PW label carries all the semantics to 
forward the traffic out to egress AC (i.e. tunnel label is not used for this)...
 
/himanshu

-----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Thursday, October 07, 2004 10:42 AM
To: Shah, Himanshu; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

Himanshu,

1,2 and 3 though are operations that occur at the ingress. I’m still puzzled as to how the egress knows (given any of these tunnel setup methods) over which tunnel a particular pseudowire’s datastream is going to appear. My concern is unambiguously identifying such a, newly appearing, stream. I can believe that this is possible if the label value signaled (by the egress in this case) is unique for the platform. What I’m not aware of is any statement that _requires_ this to be true. In draft-ietf-pwe3-control-protocol-10.txt the label is signaled as a “Generic Label”. Does anyone know if there are semantics associated with that type of label or its use that require it to be unique? 

And I’ll take a look at your draft….

thanks

Pd 

-----Original Message-----
From: Shah, Himanshu [mailto:[email-masked]] 
Sent: Thursday, October 07, 2004 9:08 AM
To: Paul Doolan; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

2) do BE tunnels

/himanshu

-----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Wednesday, October 06, 2004 4:45 PM
To: [email-masked]
Subject: [PWE3] PW to PSN mapping (again)

Hello,

 

Paul

  _____  

  _____

---

From: Sasha Vainshtein <[email-masked]>
Date: Thu, 7 Oct 2004 17:13:35 +0200

Paul,
I quote the following text from Section 3 "The Pseudowire Label"
of draft-ietf-pwe3-control-protocol-10.txt:

<quote>
   Note that the PW label must always be at the bottom of the packet's
   label stack and labels MUST be allocated from the per-platform label
   space.
<end quote>

IMHO this specifically answers your concerns and explains why
egress PE does not require the knowledge of the actual transport
LSP over which the specific PW instance is delivered to it.

Regards,
                              Sasha
-----Original Message-----
From: Paul Doolan
To: Shah, Himanshu; [email-masked]
Sent: 10/7/2004 4:42 PM
Subject: RE: [PWE3] PW to PSN mapping (again)

Himanshu,

1,2 and 3 though are operations that occur at the ingress. I’m still
puzzled as to how the egress knows (given any of these tunnel setup
methods) over which tunnel a particular pseudowire’s datastream is going
to appear. My concern is unambiguously identifying such a, newly
appearing, stream. I can believe that this is possible if the label
value signaled (by the egress in this case) is unique for the platform.
What I’m not aware of is any statement that _requires_ this to be true.
In draft-ietf-pwe3-control-protocol-10.txt the label is signaled as a
“Generic Label”. Does anyone know if there are semantics associated with
that type of label or its use that require it to be unique? 

thanks

Pd 

-----Original Message-----
From: Shah, Himanshu [mailto:[email-masked]] 
Sent: Thursday, October 07, 2004 9:08 AM
To: Paul Doolan; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

      PWs (of same characteristics) over it.  You can apply thresholds
that

2) do BE tunnels

One of the thing an ingress PE may want to take into consideration is AC
characteristics

of Egress PE when selecting a transport tunnel from ingress to egress
and for

applying appropriate traffic policing/shaping at ingress (to avoid
packet drops at egress). 

 For this you may want to look at
draft-shah-PWE3-pw-qos-signalling-00.txt. (peddling my draft..:-)

/himanshu

-----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Wednesday, October 06, 2004 4:45 PM
To: [email-masked]
Subject: [PWE3] PW to PSN mapping (again)

Hello,

It’s been a while since I’ve been active in this area but the
fascinating RSVP-TE thread makes it seem like I never left. Didn’t we
see the RSVP vs LDP movie already? Still it’s nice to see that some of
the original combatants are around to clarify the record. Today however
I have no questions about RSVP.

I would be grateful if any of you can shed some light on a thing that’s
been puzzling me for a little while. Back in August there was a little
thread “[PWE3] PW to PSN tunnel mapping” started by Benny Lønstrup
Ammitzbøll. He asked how a PE might know to which PSN tunnel a PW
belongs. Before that thread morphed into the QoS one there was an
uchallenged contribution that said it was a matter of local policy at
the PE which decided this mapping. 

Matters of local policy tend to create interoperability problems. In
particular this one (if true) might be better stated as “it’s a matter
of local policy at the ingress (to which PSN tunnel a PW is mapped)”.
And the corollary is surely that the egress is SOL in the ‘local policy’
department. Perhaps more accurately the egress’s policy options are
binary. It can take pseudowire traffic as and from whence it arrives or
it can drop it.

Is it really the case that I can open up multiple tunnels to an egress
PE and fire off pseudowire traffic down whichever of them I choose and
everything will work fine? Or does this depend not only on the local
policy of the ingress but also on the vendor implementation at the
egress? 

Paul

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named. If you are not the named addressee you should not disseminate,
distribute or copy this email. Please notify the sender immediately if
you received this message by mistake and delete this e-mail from your
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06492. www.mangrovesystems.com

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distribute or copy this email. Please notify the sender immediately if
you received this message by mistake and delete this e-mail from your
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---

From: "Paul Doolan" <[email-masked]>
Date: Thu, 7 Oct 2004 11:45:14 -0400

Sasha,

                             Sasha
 
This certainly answers one question. The mechanism exists and I
apologise for not noticing that. The question as to what implementations
actually do still remains though..

Thanks
Pd

---

From: "Paul Doolan" <[email-masked]>
Date: Thu, 7 Oct 2004 12:38:16 -0400

Himanshu,

>an egress PE will get the PW traffic.

I can see how that might be useful.

>forward the traffic out to egress AC (i.e. tunnel label is not used for
this)...

I don't actually think it is necessary....... if (somewhere) there was a
specification that said that in that case where multiple tunnels from
the an ingress PE terminate on the (same) egress PE then that PE can
make no assumptions about the tunnel on which traffic from a particular
PW can arrive. Absent that we rely on policy and implementation choice.
Given the unique nature of the label as pointed out by Sasha and the PHP
behavior, maybe the point is moot but I still have a nagging feeling
that expected behavior in this scenario is underspecified.  

BTW: Apologies to all for the boilerplate verbiage at the bottom of
this.

I'm working on getting it removed. 

pd

---

From: "Choudhary, Aseem (Aseem)" <[email-masked]>
Date: Fri, 8 Oct 2004 12:55:34 +0530

I have a question:
 
 If PW can take any PSN tunnel reachable to egress PE(assuming multiple PSN
Tunnels from ingress PE to egress PE are available), then which PSN tunnel
should be configured ( data plane) at egress PE to receive a particular PW
label.One obvious option is static configuration where we bind PW label
(inner label) to the PSN tunnel(outer label). The other option could be PW
signalling should support which PSN tunnel it would take.
 
Aseem
 
 -----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Thursday, October 07, 2004 10:08 PM
To: Shah, Himanshu; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

Himanshu,

I don't actually think it is necessary....... if (somewhere) there was a
specification that said that in that case where multiple tunnels from the an
ingress PE terminate on the (same) egress PE then that PE can make no
assumptions about the tunnel on which traffic from a particular PW can
arrive. Absent that we rely on policy and implementation choice. Given the
unique nature of the label as pointed out by Sasha and the PHP behavior,
maybe the point is moot but I still have a nagging feeling that expected
behavior in this scenario is underspecified.  

BTW: Apologies to all for the boilerplate verbiage at the bottom of this.

pd

  _____  

This message contains information intended only for the individual named. If
you are not the named addressee you should not disseminate, distribute or
copy this email. Please notify the sender immediately if you received this
message by mistake and delete this e-mail from your system. The sender does
not accept liability for any errors or omissions in the contents of this
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Fairfield Blvd, Wallingford, CT 06492. www.mangrovesystems.com

---

From: Benny Ammitzboll <[email-masked]>
Date: Fri, 8 Oct 2004 11:06:23 +0200

The answer is: None, because the egress PE does not need to know (in fact,
in some systems it does not know) on which PSN tunnel the packet with a PW
label was received. The PW label uniquely identifies the PW in the egress
PE.

Note that this also allows the ingress PE to select another PSN tunnel
without any signaling from the ingress to the egress PE.

Regards,

Benny Ammitzboll

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of
Choudhary, Aseem (Aseem)
Sent: 8. oktober 2004 09:26
To: [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

I have a question:

Aseem

 -----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Thursday, October 07, 2004 10:08 PM
To: Shah, Himanshu; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

Himanshu,

>forward the traffic out to egress AC (i.e. tunnel label is not used for
this)...

I don't actually think it is necessary... if (somewhere) there was a

pd

---

From: Sasha Vainshtein <[email-masked]>
Date: Fri, 8 Oct 2004 19:58:35 +0200

Aseem,
I have a counter-question:
Why do you think the egress PE should require any binding
between the PSN tunnel and the PW label?

IMHO, no such binding is required (and hence no method to achieve it
is provided:-). Instead, the PW labels are allocated from the per-platform
space. And, as Himanshu has just explained, in certain cases such a
binding would be definitely harmful.

Regards,
               Sasha
-----Original Message-----
From: Choudhary, Aseem (Aseem)
To: [email-masked]
Sent: 10/8/2004 9:25 AM
Subject: RE: [PWE3] PW to PSN mapping (again)

I have a question:
 
 If PW can take any PSN tunnel reachable to egress PE(assuming multiple
PSN Tunnels from ingress PE to egress PE are available), then which PSN
tunnel should be configured ( data plane) at egress PE to receive a
particular PW label.One obvious option is static configuration where we
bind PW label (inner label) to the PSN tunnel(outer label). The other
option could be PW signalling should support which PSN tunnel it would
take.
 
Aseem
 
 -----Original Message-----
From: Paul Doolan [mailto:[email-masked]]
Sent: Thursday, October 07, 2004 10:08 PM
To: Shah, Himanshu; [email-masked]
Subject: RE: [PWE3] PW to PSN mapping (again)

Himanshu,

pd

  _____  

 <<ATT86434.txt>>