During Auth 48, the authors of
draft-ietf-pwe3-static-pw-status found some issues
with the acknowledgement procedures in Section 5.3
of the draft that we feel should be addressed before
publication. Since the draft has already been
through WG and IETF last call, we would like to
highlight the proposed changes to the working group
and solicit feedback.
Section 5.3, 3rd paragraph:
Reason for change:
The current suggested default refresh timer value
is too short to allow scaling
to very large numbers of PWs while minimising the
overhead. It is also inconsistent
with the suggested default requested in an ACK
packet. Therefore we suggest increasing
the default to 600secs.
OLD: The suggested default value for the refresh
timer is 30 seconds.
NEW: The suggested default value for the refresh
timer is 600 seconds.
Section 5.3, 4th paragraph:
Reason for change:
The current text requires that a receiving PE must
acknowledge a PW status message
of 'clear all faults' in order to force a
transmitter to stop sending PW status
messages at 1 second intervals. We are concerned
that a mandatory acknowledgement
adds an unnecessary complexity to the protocol
which is inconsistent with
the use of the acknowledgement as per the following
section (5.3.1). Additionally,
we are also concerned that this may cause problems
if a transmitter
is flapping between 'clear all faults' and a
non-zero value, and if the
acknowledgement is lost. We therefore suggest that
the acknowledgement to
'clear all faults' be made optional, and that the
transmitter behavior be changed so
that it sends up to 3 status messages of zero in a
row, and then goes silent.
OLD:
To clear a particular status fault, the PE need
only send an
updated message with the corresponding bit cleared.
If the PW status
code is zero, the PW OAM message will be sent like
any other PW OAM
status message using the procedures described
above; however, it MUST be
acknowledged with a packet with a timer value of
zero. This will cause
the PE sending the PW status notification message
with a PW status code
equal to zero to stop sending and to continue
normal operation.
NEW:
To clear a particular status fault, the PE need
only send an
updated message with the corresponding bit cleared.
If the PW status
code is zero, the PW OAM message will be sent like
any other PW OAM
status message using the procedures described
above; however,
transmission will cease after 3 PW status messages
have been sent. A PW
status message of zero MAY be acknowledged as per
the procedures described
in Section 5.3.1. If it is acknowledged, then a
timer
value of zero MUST be used. This SHOULD cause the
PE sending the PW status
notification message with a PW status code equal to
zero to stop sending
and to continue normal operation.
Section 5.3.1, 1st paragraph:
Reason for change:
The procedures currently defined in this paragraph
can lead to a receiver
of the static status message timing out if it
requests, throught the use of the
ACK mechanism, a longer refresh timer from the
transmitter. This is because the
current text implies that the transmitter change
its referesh timer immediately
on receipt of the ack packet from the receiver. The
new text clarifies that
the refresh timer be updated at the end of the
current refresh interval, as
well as making some other editorial clarifications.
OLD:
The PE receiving a PW OAM message containing a PW
status message
can acknowledge the PW status message by simply
building an almost
identical reply packet with the A bit set, and
transmitting it on the PW
ACH back to the source of the PW status message.
The timer value set in
the reply packet SHOULD then be used by the PE as
the new transmit
interval. If the transmitting PE does not want to
use the new timer
value (for local policy reasons, or because it
simply cannot support
it), it MUST refresh the PW OAM message with the
timer value it desires.
The receiving PE will then set its timeout timer
according to the timer
value that is in the packet received, regardless of
what timer value it
sent. The receiving PE MUST NOT retry to set the
timer value more than
once per timer value.
NEW:
A PE receiving a PW OAM message containing a PW
status message MAY
acknowledge the PW status message by simply
building a reply packet
with the same format and status code as the
received PW OAM message,
but with the A bit set, and transmitting it on the
PW ACh back
to the source of the PW OAM message. The receiving
PE MAY use the
refresh timer field in the acknowledgement packet
to request a new
refresh interval from the originator of the PW OAM
message. The timer
value set in the reply packet SHOULD then be used
by the originator of
the PW OAM message as the new transmit interval.
If the requested
refresh timer value is used, the PW OAM message
transmission interval is
only set to the new value and the new value sent in
the next PW OAM
message, when the current timer expires. If the
transmitting PE does not
want to use the new timer value (for local policy
reasons, or because it
simply cannot support it), it MUST refresh the PW
OAM message with the
timer value it desires. The receiving PE will then
set its timeout timer
according to the new refresh timer value that is in
the packet received,
regardless of what timer value it requested. The
receiving PE MUST NOT
request a new refresh timer value more than once
per refresh interval.