[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: Last call - RSVP problems
Hi Jonathan,
What needs to be detected here is the inability to send and
receive signaling messages to and from your RSVP peer. In this
respect, using RSVP Hello is a more accurate mechanism for
detecting failures since it is part of the RSVP protocol and
independent of the link layer used to realize the control
channel. As you point out, if you prefer redundant control
channels for resiliency, and want to rely on LMP only, you have
to correlate all LMP detected failures in order to declare a
control channel failure. With RSVP Hello you would rely on a
single set of event(s) to detect the failure.
To go even further, what if all your control channels are working
fine, but your RSVP daemon has crashed, for whatever reason.
LMP hellos will keep going across but RSVP messages will not...
All this points to the (certainly non-trivial) problem of failure
detection and correlation at different layers. I am not trying to
say that RSVP Hello is the perfect or only mechanism we should rely
on, but it certainly has a place in addressing the problem.
Thanks,
Dimitris
PS. Hopefully we are not too far apart so we might not have
to keep the discussion going for too long :-)
In any case I believe it has some relevance here as well.
> -----Original Message-----
> From: Jonathan Lang [mailto:jplang@calient.net]
> Sent: Friday, May 25, 2001 6:56 PM
> To: 'Dimitrios Pendarakis'; Jonathan Lang; 'Fong Liaw'; 'suresh
> Katukam'; v.sharma@ieee.org
> Cc: 'Jennifer Yates'; mpls@UU.NET; ccamp@ops.ietf.org
> Subject: RE: Last call - RSVP problems
>
>
> Dimitris,
> The RSVP Hello Extension is intended to detect node failures and not
> necessarily link (control channel) failures. In particular,
> the tunnel
> draft says, "It should be noted that node failure detection
> is not the same
> as a link failure detection mechanism, particularly in the
> case of multiple
> parallel unnumbered links." What happens if you want
> redundant control
> channels for control-channel resiliency? I believe you would
> still want a
> mechanism to detect control channel (link-layer) failures.
>
> In LMP, you can have multiple active control channels
> between a pair of
> nodes. You can configure control channels over shared
> Ethernet and over
> SONET/SDH overhead, etc. You send keep-alive Hellos over each control
> channel. If you so desire, you can send all signaling
> messages over the
> Ethernet control channels. You can also choose to send all
> remaining LMP
> messages over the SONET/SDH-based control channels. Keeping
> RSVP Hellos as
> "optional" would be fine. Making them mandatory doesn't seem
> like the right
> solution.
>
> Thanks,
> Jonathan
>
> P.S. Should we move this discussion on the OIF list??
>
> > -----Original Message-----
> > From: Dimitrios Pendarakis [mailto:DPendarakis@tellium.com]
> > Sent: Friday, May 25, 2001 3:16 PM
> > To: 'Jonathan Lang'; 'Fong Liaw'; 'suresh Katukam';
> v.sharma@ieee.org
> > Cc: 'Jennifer Yates'; mpls@UU.NET; ccamp@ops.ietf.org
> > Subject: RE: Last call - RSVP problems
> >
> >
> > Hi Jonathan,
> >
> > One point to consider is that the signaling control
> > channel might be realized over a different link layer
> > than LMP. For example, LMP might be running in-fiber
> > over SONET/SDH overhead bytes, while RSVP is running
> > over an out-of-band network such a shared Ethernet.
> > RSVP Hello allows independent detection of signaling
> > channel failure, so it's a useful option to keep.
> >
> > Thanks,
> > Dimitris
> >
> > Dimitris Pendarakis
> > Tellium, Inc.
> >
> >
> > > -----Original Message-----
> > > From: Jonathan Lang [mailto:jplang@calient.net]
> > > Sent: Friday, May 25, 2001 5:30 PM
> > > To: 'Fong Liaw'; 'suresh Katukam'; v.sharma@ieee.org
> > > Cc: 'Jennifer Yates'; mpls@UU.NET; ccamp@ops.ietf.org
> > > Subject: RE: Last call - RSVP problems
> > >
> > >
> > > Fong,
> > >
> > >
> > > <snip>
> > > > Same as (2), any proposals that remove the refresh mechanism
> > > > is going to be difficult to prove that all cases are covered.
> > > >
> > > > Instead, we (will) recommend the following in OIF UNI document:
> > > >
> > > > Use RSVP Hello to detect control channel failure.
> > > Why wouldn't you use the LMP Hello to detect control channel
> > > failure? This
> > > is exactly what it is designed for. From
> > > draft-ietf-mpls-lsp-tunnel-08.txt,
> > >
> > > "This (RSVP Hello) mechanism is intended to be used when
> > > notification of
> > > link layer
> > > failures is not available and unnumbered links are not
> > > used, or when
> > > the failure detection mechanisms provided by the link
> > layer are not
> > > sufficient for timely node failure detection."
> > >
> > > > If a control channel failure is detected, LSPs states
> > > > are maintained as if a node continues to receive
> > > > RSVP refresh message from the failed control channel.
> > > > The recommended Hello timer will be in second range,
> > > > instead of ms range specified in RSVP-TE draft.
> > > >
> > > > If a control channel failed permanently, manual intervention
> > > > may be required. This is to be studied.
> > > >
> > > > p.s The text is currently being drafted as we type.
> > >
> >
>