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RE: [PWE3] Last Call: <draft-ietf-pwe3-redundancy-bit-06.txt> (Pseudowire Preferential Forwarding Status Bit) to Proposed Standard

2012-04-25 12:29:07
Dear all,
I have made a couple more clarifications to the text below based on additional 
feedback from Daniel on the use of the active PW selection algorithm in use 
cases presented in Section 15.

I am copying the new updated Section 5.1. All the changes from the current 
version of the draft are underlined.

Let me  know if you have any comments.

Regards,
Mustapha.
=======================================================================================
5.1. Independent Mode:
PW endpoint nodes independently select which PWs are eligible to become active 
and which are not. They advertise the corresponding Active or Standby 
preferential forwarding status for each PW. Each PW endpoint compares local and 
remote status bits and uses the PW that is UP at both endpoints and that 
advertised Active preferential forwarding status at both the local and remote 
endpoints.
In this mode of operation, the preferential forwarding status indicates the 
preferred forwarding state of each endpoint but the actual forwarding state of 
the PW is the result of the comparison of the local and remote forwarding 
status bits.
If more than one PW qualifies for the Active state, each PW endpoint MUST 
implement a common mechanism to choose the PW for forwarding. The default 
mechanism MUST be supported by all implementations and operates as follows:
1.     For FEC128 PW, the PW with the lowest pw-id value is selected.
2.     For FEC129 PW, each PW in a redundant set is uniquely identified at each 
PE using the following triplet: AGI::SAII::TAII. The unsigned integer form of 
the concatenated word can be used in the comparison. However, the SAII and TAII 
values as seen on a PE node are the mirror values of what the peer PE node 
sees. To have both PE nodes compare the same value we propose that the PE with 
the lowest system IP address use the unsigned integer form of AGI::SAII::TAII 
while the PE with the highest system IP address use the unsigned integer form 
of AGI::TAII::SAII. This way, both PEs will compare the same values. The PW 
which corresponds to the minimum of the compared values across all PWs in the 
redundant is selected.
Note 1: in the case where the system IP address is not known, it is recommended 
to implement the optional active PW selection mechanism described next.
Note 2: in the case of segmented PW, the operator needs to make sure that the 
pw-id or AGI::SAII::TAII of the redundant PWs within the first and last segment 
are ordered consistently such that the same end-to-end MS-PW gets selected. 
Otherwise, it is recommended to implement the optional active PW selection 
mechanism described next.
The PW endpoints MAY also implement the following optional active PW selection 
mechanism.
1.     If the PW endpoint is configured with the precedence parameter on each 
PW in the redundant set, it must select the PW with the lowest configured 
precedence value.
2.     If the PW endpoint is configured with one PW as primary and one or more 
PWs as secondary, it must select the primary PW in preference to all secondary 
PWs. If a primary PW is not available, it must use the secondary PW with the 
lowest precedence value. If the primary PW becomes available, a PW endpoint 
must revert to it immediately or after the expiration of a configurable delay.
3.     This active PW selection mechanism assumes the precedence parameter 
values are configured consistently at both PW endpoints and that unique values 
are assigned to the PWs in the same redundancy set to achieve tie-breaking 
using this mechanism.
There are scenarios with dual-homing of a CE to PE nodes where each PE node 
needs to advertise Active preferential forwarding status on more than one PW in 
the redundancy set. However, a PE MUST always select a single PW for forwarding 
using the above active PW selection algorithm. An example of such a case is 
described in 15.2. .
There are scenarios where each PE needs to advertize Active preferential 
forwarding status on a single PW in the redundancy set. In order to ensure that 
both PE nodes make the same selection, they MUST use the above active PW 
selection algorithm to determine the PW eligible for active state. An example 
of such a case is described in 15.5. .
In steady state with consistent configuration, a PE will always find an active 
PW. However, it is possible that such a PW is not found due to a 
mis-configuration. In the event that an active PW is not found, a management 
indication SHOULD be generated. If a management indication for failure to find 
an active PW was generated and an active PW is subsequently found, a management 
indication should be generated, so clearing the previous failure indication. 
Additionally, a PE may use the optional request switchover procedures described 
in Section 6.3. to have both PE nodes switch to a common PW.
There may also be transient conditions where endpoints do not share a common 
view of the Active/Standby state of the PWs. This could be caused by 
propagation delay of the T-LDP status messages between endpoints. In this case, 
the behavior of the receiving endpoint is outside the scope of this document.
Thus, in this mode of operation, the following definition of Active and Standby 
PW states apply:
o          Active State
A PW is considered to be in Active state when the PW labels are exchanged 
between its two endpoints and the status bits exchanged between the endpoints 
indicate the PW is UP and its preferential forwarding status is Active at both 
endpoints. In this state user traffic can flow over the PW in both directions. 
As described in Section 5.1. , the PE nodes must implement a common mechanism 
to select one PW for forwarding in case multiple PWs qualify for the Active 
state.
o          Standby State
A PW is considered to be in Standby state when the PW labels are exchanged 
between its two endpoints, but the Preferential Forwarding status bits 
exchanged indicate the PW preferential forwarding status is Standby at one or 
both endpoints. In this state the endpoints MUST NOT forward data traffic over 
the PW but MAY allow PW OAM packets, e.g., Virtual Connection Connectivity 
Verification (VCCV) packets [10], to be sent and received in order to test the 
liveliness of standby PWs. The endpoints of the PW may also allow the 
forwarding of specific control plane packets of applications using the PW. The 
specification of applications and the allowed control plane packets is outside 
the scope of this document. If the PW is a spoke in H-VPLS, any MAC addresses 
learned via the PW SHOULD be flushed when it transitions to Standby state 
according to the procedures in RFC4762 [3] and [9].
=======================================================================================
________________________________
From: Aissaoui, Mustapha (Mustapha)
Sent: Thursday, March 22, 2012 11:59 AM
To: 'pwe3(_at_)ietf(_dot_)org'; Daniel Cohn
Cc: 'stbryant(_at_)cisco(_dot_)com'; 
'draft-ietf-pwe3-redundancy-bit(_at_)tools(_dot_)ietf(_dot_)org'; 
'ietf(_at_)ietf(_dot_)org'; 'Andrew G. Malis'
Subject: RE: [PWE3] Last Call: <draft-ietf-pwe3-redundancy-bit-06.txt> 
(Pseudowire Preferential Forwarding Status Bit) to Proposed Standard

Dear all,
I received comments from Daniel regarding the intended use of the optional 
active PW selection mechanism in section 5.1. I pasted below the corresponding 
paragraph of Section 5.1 with the changes we agreed to underlined.

He also asked if the default active PW selection mechanism should be referenced 
in Section 5.2 with the Master/Slave mode of operation. Although, it is not 
stricly required for interoperability, implementations would benefit from a 
consistent behaviour. I used SHOULD in that case. The text is also pasted below 
with the changes underlined.

Let me know if you have any comments on this.

Regards,
Mustapha.

=======================================================================================
I. Changes to Section 5.1 - 3rd paragraph:
"
If more than one PW qualifies for the Active state, each PW endpoint MUST 
implement a common mechanism to choose the PW for forwarding. The default 
mechanism MUST be supported by all implementations and operates as follows:
1.     For FEC128 PW, the PW with the lowest pw-id value is selected.
2.     For FEC129 PW, each PW in a redundant set is uniquely identified at each 
PE using the following triplet: AGI::SAII::TAII. The unsigned integer form of 
the concatenated word can be used in the comparison. However, the SAII and TAII 
values as seen on a PE node are the mirror values of what the peer PE node 
sees. To have both PE nodes compare the same value we propose that the PE with 
the lowest system IP address use the unsigned integer form of AGI::SAII::TAII 
while the PE with the highest system IP address use the unsigned integer form 
of AGI::TAII::SAII. This way, both PEs will compare the same values. The PW 
which corresponds to the minimum of the compared values across all PWs in the 
redundant is selected.
Note 1: in the case where the system IP address is not known, it is recommended 
to implement the optional active PW selection mechanism described next.
Note 2: in the case of segmented PW, the operator needs to make sure that the 
pw-id or AGI::SAII::TAII of the redundant PWs within the first and last segment 
are ordered consistently such that the same end-to-end MS-PW gets selected. 
Otherwise, it is recommended to implement the optional active PW selection 
mechanism described next.
The PW endpoints MAY also implement the following optional active PW selection 
mechanism.
1.     If the PW endpoint is configured with the precedence parameter on each 
PW in the redundant set, it must select the PW with the lowest configured 
precedence value.
2.     If the PW endpoint is configured with one PW as primary and one or more 
PWs as secondary, it must select the primary PW in preference to all secondary 
PWs. If a primary PW is not available, it must use the secondary PW with the 
lowest precedence value. If the primary PW becomes available, a PW endpoint 
must revert to it immediately or after the expiration of a configurable delay.
3.     This active PW selection mechanism assumes the precedence parameter 
values are configured consistently at both PW endpoints and that unique values 
are assigned to the PWs in the same redundancy set to achieve tie-breaking 
using this mechanism.
"

II. Changes to Section 5.2 - 5th paragraph:
"
If more than one PW qualify for the Active state, the Master PW endpoint node 
selects one. There is no requirement to specify a default active PW selection 
mechanism in this case but for consistency across implementations, the Master 
PW endpoint SHOULD implement the default active PW selection mechanism 
described in Section 5.1.
If the Master PW endpoint implements the optional active PW selection mechanism 
based on primay/secondary and precedence parameters, it MUST follow the 
following behaviour:
1.     If the PW endpoint is configured with the precedence parameter on each 
PW in the redundant set, it must select the PW with the lowest configured 
precedence value.
2.     If the PW endpoint is configured with one PW as primary and one or more 
PWs as secondary, it must select the primary PW in preference to all secondary 
PWs. If a primary PW is not available, it must use the secondary PW with the 
lowest precedence value. If the primary PW becomes available, a PW endpoint 
must revert to it immediately or after the expiration of a configurable delay.
"
=======================================================================================

________________________________
From: Aissaoui, Mustapha (Mustapha)
Sent: Wednesday, March 07, 2012 12:56 PM
To: Andrew G. Malis
Cc: stbryant(_at_)cisco(_dot_)com; 
draft-ietf-pwe3-redundancy-bit(_at_)tools(_dot_)ietf(_dot_)org; 
pwe3(_at_)ietf(_dot_)org; ietf(_at_)ietf(_dot_)org
Subject: RE: [PWE3] Last Call: <draft-ietf-pwe3-redundancy-bit-06.txt> 
(Pseudowire Preferential Forwarding Status Bit) to Proposed Standard

makes sense Andy.

Thanks,
Mustapha.

________________________________
From: Andrew G. Malis [mailto:amalis(_at_)gmail(_dot_)com]
Sent: Wednesday, March 07, 2012 12:53 PM
To: Aissaoui, Mustapha (Mustapha)
Cc: stbryant(_at_)cisco(_dot_)com; 
draft-ietf-pwe3-redundancy-bit(_at_)tools(_dot_)ietf(_dot_)org; 
pwe3(_at_)ietf(_dot_)org; ietf(_at_)ietf(_dot_)org
Subject: Re: [PWE3] Last Call: <draft-ietf-pwe3-redundancy-bit-06.txt> 
(Pseudowire Preferential Forwarding Status Bit) to Proposed Standard

Mustapha,

You might want to wait for any other LC comments before updating.

Thanks,
Andy

On Wed, Mar 7, 2012 at 9:49 AM, Aissaoui, Mustapha (Mustapha) 
<mustapha(_dot_)aissaoui(_at_)alcatel-lucent(_dot_)com<mailto:mustapha(_dot_)aissaoui(_at_)alcatel-lucent(_dot_)com>>
 wrote:
Ooops. Thank you for pointing this out Stewart. I will make the update and 
publish a new revision.

Mustapha.

-----Original Message-----
From: Stewart Bryant 
[mailto:stbryant(_at_)cisco(_dot_)com<mailto:stbryant(_at_)cisco(_dot_)com>]
Sent: Wednesday, March 07, 2012 12:48 PM
To: 
draft-ietf-pwe3-redundancy-bit(_at_)tools(_dot_)ietf(_dot_)org<mailto:draft-ietf-pwe3-redundancy-bit(_at_)tools(_dot_)ietf(_dot_)org>
Cc: ietf(_at_)ietf(_dot_)org<mailto:ietf(_at_)ietf(_dot_)org>; 
pwe3(_at_)ietf(_dot_)org<mailto:pwe3(_at_)ietf(_dot_)org>
Subject: Re: Last Call: <draft-ietf-pwe3-redundancy-bit-06.txt> (Pseudowire 
Preferential Forwarding Status Bit) to Proposed Standard


Authors

There was on point that I notice that you did not address from the AD review 
and so I am picking it up as a LC comment:

In section 10 you say:

   "This document makes the following update to the PwOperStatusTC
   textual convention in RFC5542 [8]: "

This update should be recorded in the metadata (top left front page) and it is 
usual to put a one line note in the abstract.

Stewart



On 07/03/2012 17:00, The IESG wrote:
The IESG has received a request from the Pseudowire Emulation Edge to
Edge WG (pwe3) to consider the following document:
- 'Pseudowire Preferential Forwarding Status Bit'
   <draft-ietf-pwe3-redundancy-bit-06.txt>  as a Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf(_at_)ietf(_dot_)org<mailto:ietf(_at_)ietf(_dot_)org> mailing lists by 
2012-03-21. Exceptionally, comments may
be sent to iesg(_at_)ietf(_dot_)org<mailto:iesg(_at_)ietf(_dot_)org> instead. 
In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


    This document describes a mechanism for standby status signaling of
    redundant pseudowires (PWs) between their termination points. A set
    of redundant PWs is configured between provider edge (PE) nodes in
    single-segment pseudowire (SS-PW) applications, or between
    terminating provider edge (T-PE) nodes in multi-segment pseudowire
    (MS-PW) applications.

    In order for the PE/T-PE nodes to indicate the preferred PW to use
    for forwarding PW packets to one another, a new status bit is needed
    to indicate a preferential forwarding status of Active or Standby for
    each PW in a redundant set.

    In addition, a second status bit is defined to allow peer PE nodes to
    coordinate a switchover operation of the PW.






The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-pwe3-redundancy-bit/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-pwe3-redundancy-bit/ballot/


No IPR declarations have been submitted directly on this I-D.


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