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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