The MPLS WG Archive

["Matthew R. Meyer" <mmeyer@gblx.net>]

Comments inline...

Thus spake Curtis Villamizar (curtis@fictitious.org):

 |
 |In message <Pine.LNX.4.44.0302191431560.3611-100000@fido.nc.rr.com>, Jim Boyle 
 |writes:
 |> 
 |> First, great draft - I like this concept.
 |> 
 |> While a flag might be just the right thing for this particular
 |> application, I wonder if it might be good to try to broaden 
 |> soft preemption technique to include other polite preemptions.
 |> 
 |> These might include the following indicators
 |> 
 |> o) your LSP is being prempted on the indicated link (draft covers)
 |> o) your LSP should be rerouted, this node is shutting down
 |> o) your LSP should be rerouted, this link is being taken out of
 |>    service
 |> o) your LSP should be rerouted away from this node (administrative/CLI)
 |> o) your LSP should be rerouted away from this link (administrative/CLI)
 |> 
 |> You can somewhat do some of these by changing metrics and waiting, but
 |> just was wondering if something more general might be useful.
 |
 |Why couldn't you just use the same bit and allow soft preemption on
 |link shut, reload, 

Or OL bit set...

 |CLI administrative without encoding the reason?
 |Since these are all CLI initiated, it wouldn't hurt to delay.
 |Alternately, the soft preempt on anything using a specific resource
 |could be done.
 |Link bundle lost a member might also qualify as a reason for soft
 |preemption for implementations of link bundling that can transparently
 |more flows to other members of the bundle.
 
I think there is value in conveying to the head-end the population 
category of the soft preemption (Single LSP|Link|Bundle Member|SRLG|
Node). Doing so provides prompt, more accurate info for the head-end
to use when trying to quickly find the new valid path for the first 
of (say) 30 arriving soft preemptions. 

    .---,A     .---,B
    |   |---1--|   |----- 
    |   |---2--|   |-----
    `---'      `---'
     HE        Maint

fe. Imagine we cause all LSPs transiting a node B to be soft preempted 
in prep for maintenance. HE A's LSPs all transited a certain circuit (1)
to the maintenance node B, however there is a parallel circuit as well(2).
Without the "node" flag, we might amend the HE TE-DB zeroing (1)s 
reservable BW (the circuit for which we were just soft preempted)
when we should have zeroed out (2) as well. The result could be our
soft preemption make before break sets up (or tries to) through the 
maintenance node despite being recently soft preempted off it..

Technically a HE need only receive the first LSP population oriented 
flag (Node|SRLG|etc) soft preemption to discover 1) what subset of 
locally originating LSPs need to be rerouted and 2) what links/nodes/
members need to be avoided. There is still a need for one-at-a-time
straight soft preemption of course. 

 |> Also, with Diffserv TE, not sure that one can assume that a preemption
 |> necessarily "implies exhausted bandwidth at the affected priority
 |> level *and greater*" (section 5), but local implementations can do
 |> as they please I suppose.
 |
 |Agreed.  The "and greater" should be dropped.

okay. Agreed.

Thanks 
Matthew

 |
 |> regards,
 |> 
 |> Jim
 |
 |Thanks,
 |
 |Curtis