The MPLS WG Archive

[Ping Pan <pingpan@cs.columbia.edu>]

On Mon, 14 Jul 2003, Der-Hwa Gan wrote:
> If we take a look at rule 2 - 6, all they try to do is to identify the
> protected LSP from a set of Path messages that contain all possible mutations
> of FAST_REROUTE and/or DETOUR objects. And the rules look confusing
> because they assume the worst possible case situations.
>
>      2. If one LSP is originated from this node, this must be
>         the final LSP. Quit.
>
>      3. If only one Path message contains FAST_REROUTE object, this
>         becomes the chosen Path message. Quit.
>
>      4. If there are several LSPs, and not all of them have a DETOUR
>         object, then eliminate those with DETOUR from consideration.
>
>      5. If several candidates remain (that is, there are both detour
>         and protected LSPs), prefer the ones with FAST_REROUTE object.
>
>      6. If none found, prefer the ones without DETOUR object. If none
>         found, prefer the ones with DETOUR object.
>
> I think some simplification is possible, if we simply suggest the guidelines
> (but not the details) of finding the protected LSP. As long as protected LSP(s)
> are preferred over detours, there should not be inter-op problems.
>
>      1.  If only one of the Path messages is for the protected LSP
>          (a protected LSP is one originated from this node, or with
> 	 the FAST_REROUTE object, or without the DETOUR object) then this
> 	 becomes the chosen Path message.  Quit.
>
>      2.  If more than one protected LSPs found, eliminate detours (those
> 	 with the DETOUR object) from consideration.
>
>      3.  From the remaining set of Path messages, eliminate from consideration
> 	 any that traverse nodes that others want to avoid.
>
>      4.  If several still remain, it is a local decision to
>          choose which one to forward.
>

Der-Hwa,

I think this is a whole lot better. If Nic and Alia have no problem,
let's fold the new rules into the next version.

Thanks!

- Ping

>
> This way, 1 & 2 replace the original rule 2-6. The original rule 1 becomes
> 3, and the original rule 7 becomes 4.
>
> The benefits are (a) it is more readable, (b) implementations for rule 1&2 can
> be quite simple if the worst case situations (suggested in original 2-6) won't
> exist in that implementation.
>
> Will this look ok to all?
>
> Thanks,
> Der-Hwa
>
>
> >
> > Thanks!
> >
> > - Ping
> >
> > > Thanks,
> > > Der-Hwa Gan
> > >
> >
>