Re: [RPRWG] Wait To Restore
John,
| any other uses for WTR?) The only new idea being introduced is possibly
| changing the value for the WTR timer based on recent events on the link,
| which I think we all agree should be possible, but handled outside of the
| standard.
But it should be mentioned in the spec.
Manav
|
| jl
|
| -----Original Message-----
| From: George Suwala [mailto:gsuwala@xxxxxxxxx]
| Sent: Wednesday, July 31, 2002 3:52 PM
| To: John Lemon; 'Leon Bruckman'; stds-802-17@xxxxxxxx
| Cc: 'Manav Bhatia'
| Subject: RE: [RPRWG] Wait To Restore
|
|
| John,
|
| I agree with you about leaving the current WTR text as is.
|
| However Manav has brought up a good point and it may help
| if we differentiate between 2 concepts:
|
| 1. WTR, which says to the other nodes: "the link is fine, but I'm
choosing
| not to use it yet"
|
| 2. Damping of flapping of a link by keeping it in a "down" state, which
| says to the other nodes: "the link is down".
|
| Point 1 and it's dampening effect has already been covered in this thread
| (I think :-)
|
| Point 2. Such damping has only local significance and it should not
| introduce interoperability issues as each node uniquely controls
| it's own interface state.
|
| From the protocol perspective it is immaterial to this and other nodes
| if a link is declared Signal Fail (SF) because a fiber has no signal,
| or because fiber receives a perfect signal but interface circuitry
| failed and is unable to interpret it correctly, or because the node
| made an arbitrary decision to keep the interface in a SF state.
|
| It is common for a SF condition to be detected
| by software through an interrupt which is a subject to interrupt
| throttling which in fact dampens the SF state changes.
|
| So perhaps, while keeping the WTR text unchanged, we could
| add some text to the effect of: "The interface state changes
| may also be dampened by a local station by keeping the interface
| in a Signal Fail condition while the state changes frequently.
| The definition of "frequently" and the dampening algorithm are outside
| of the scope of this standard as they have no impact on the RPR protocol"
|
| What do you think?
|
| (I don't think that we should be trying to standardize the dampening
| algorithm or parameters)
|
| thanks
|
| George
|
|
| At 08:33 AM 7/31/2002 -0700, John Lemon wrote:
|
| >Leon,
| >
| >My understanding of the current text (which is hopefully correct since I
| >helped write it) is that the value that can be set for WTR is configured
on
| >a per-station basis. The basis of choosing the local value is not
| specified.
| >Therefore, it is entirely supported by the standard for a station to
alter
| >the configured WTR value on a semi-dynamic basis, such as in reaction to
| >perceived link flapping. While I agree that this client behavior is out
of
| >scope for the standard, I wanted Manav to understand that it is
supported
| by
| >the standard.
| >
| >jl
| >
| >-----Original Message-----
| >From: Leon Bruckman [mailto:leonb@xxxxxxxxxxxxx]
| >Sent: Wednesday, July 31, 2002 12:55 AM
| >To: 'John Lemon'; stds-802-17@xxxxxxxx
| >Cc: 'Manav Bhatia'
| >Subject: RE: [RPRWG] Wait To Restore
| >
| >
| >John,
| >My opinion is that we can leave the WTR as in the draft (single WTR
value).
| >As far as I know, many protection schemes operate in this way.
| >On the other hand if we accept that there is merit on performing some
type
| >of exponential backoff, or other method, it may not be only a matter of
| >implementing it at the client level (out of the standard scope), but it
may
| >need some MIB support (within standard scope).
| >
| >Leon
| >
| >-----Original Message-----
| >From: John Lemon [mailto:JLemon@xxxxxxxxxxxx]
| >Sent: Tuesday, July 30, 2002 7:17 PM
| >To: 'Manav Bhatia'; stds-802-17@xxxxxxxx
| >Subject: RE: [RPRWG] Wait To Restore
| >
| >
| >
| >Manav,
| >
| >How you set your WTR timer is up to you. If you want to have an
exponential
| >backoff each time it goes off, you can do that. If you want it the same
| each
| >time, that's fine. It doesn't matter. Regardless of what you choose,
when
| >you hold the span in WTR, the other side still "sees" it as being down
| (with
| >a state of WTR). The fact that it is an independent decision for each
| >station does not cause any problems for any other stations, any more
than
| >the fact that the span is down.
| >
| >jl
| >
| >-----Original Message-----
| >From: Manav Bhatia [mailto:manav@xxxxxxxxxxx]
| >Sent: Monday, July 29, 2002 9:07 PM
| >To: John Lemon; stds-802-17@xxxxxxxx
| >Subject: Re: [RPRWG] Wait To Restore
| >
| >
| >John,
| >After the link has flapped certain nos of times (or whatever the
criteria
| >is) we declare the link to be down i.e we damp its coming up believing
that
| >it is unstable and can go down any time. We then observe that the link
has
| >been stable for quite some time now .. so when do we make it come up
again
| >i.e when will the other links start hearing from it?
| >
| >If its left to the vendor to do that then i am afraid we can have some
| >problems.
| >
| >/Manav
| >----- Original Message -----
| >From: "John Lemon" <JLemon@xxxxxxxxxxxx>
| >To: "'Manav Bhatia'" <manav@xxxxxxxxxxx>; <stds-802-17@xxxxxxxx>
| >Sent: Tuesday, July 30, 2002 9:02 AM
| >Subject: RE: [RPRWG] Wait To Restore
| >
| >
| >| Manav,
| >|
| >| If one side of a span declares it down (due to flapping or any other
| >reason)
| >| the opposite side will learn both from the control message sent the
other
| >| way and also from the lack of keep alives. There is no
interoperability
| >| issue here.
| >|
| >| jl
| >|
| >| -----Original Message-----
| >| From: Manav Bhatia [mailto:manav@xxxxxxxxxxx]
| >| Sent: Monday, July 29, 2002 7:54 PM
| >| To: John Lemon; stds-802-17@xxxxxxxx
| >| Subject: Re: [RPRWG] Wait To Restore
| >|
| >|
| >| Hi John,
| >| If damping a flapping link is not standardized and if it is left for
the
| >| vendors to implement it the way the like then we *can* experience a
lot
| >of
| >| problems in interoperatibility between different vendors. This can
create
| >a
| >| havoc in the routing protocols. Suppose link A is flapping and vendor
X
| >| implements this link flap damp feature then it may start damping it
even
| >| when it is UP (because it has already flapped many times and has
crossed
| >a
| >| threshold). The other side knows that the link A is UP but wont
| >understand
| >| why it is not responding to the HELLOs he is sending!
| >|
| >| Moreover i feel that the various timers associated with damping a
| >flapping
| >| link should be standardized.
| >|
| >| As i mentioned before WTR is just not good enough for this purpose.
| >|
| >| ~Manav
| >| ----- Original Message -----
| >| From: "John Lemon" <JLemon@xxxxxxxxxxxx>
| >| To: "'Manav Bhatia'" <manav@xxxxxxxxxxx>; <stds-802-17@xxxxxxxx>
| >| Sent: Monday, July 29, 2002 9:38 PM
| >| Subject: RE: [RPRWG] Wait To Restore
| >|
| >|
| >| | Manav,
| >| |
| >| | There is nothing in the standard that requires or prevents this.
This
| >is
| >| | something a station could easily do, using the existing standard.
The
| >| | standard provides the basic enabling technology which can then be
built
| >| upon
| >| | by each implementer to provide many different implementations, each
| >with
| >| | their own unique values.
| >| |
| >| | jl
| >| |
| >| | -----Original Message-----
| >| | From: Manav Bhatia [mailto:manav@xxxxxxxxxxx]
| >| | Sent: Monday, July 29, 2002 7:10 AM
| >| | To: stds-802-17@xxxxxxxx
| >| | Subject: [RPRWG] Wait To Restore
| >| |
| >| |
| >| |
| >| | Hi,
| >| | Is there any proposal to damp a flapping link if it flaps beyond
some
| >| | threshold value? I am looking for exponential decay wherein if it
| >remains
| >| | stable till some time length then it will again be considered fit
for
| >| use.
| >| | IMHO we must penalize a link more if it flaps severely or more often
| >than
| >| a
| >| | link which flaps lesser number of times and less
| >| | vigorously. Using the WTR we don't differentiate between the two
cases
| >| | since both of them are advertised if they remain stable for some
time
| >| | period which is specified in the WTR.
| >| |
| >| | What do others feel about this?
| >| |
| >| | Regards,
| >| | Manav
| >| | ----
| >| | "When you are courting a nice girl an hour seems like a second. When
| >you
| >| | sit on a red-hot cinder a second seems like an hour. That's
| >relativity."
| >| |
| >| | -Albert Einstein, on relativity
| >| |