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Re: questions on draft-bryant-ipfrr-tunnels-01.txt

Subject: Re: questions on draft-bryant-ipfrr-tunnels-01.txt
From: Alia Atlas
Date: Mon, 22 Nov 2004 16:00:20 -0500
At 02:52 PM 11/22/2004, Curtis Villamizar wrote:
> >MPLS RSVP/TE FRR is loop free in the presense of unknown SRLG.  At
> >worst the fast restoration fails and a new LSP is needed from ingress
> >to egress.  So the worst case is a slow restoration but not a loop.
>
> This is true, but only for the length of the TE tunnel.  TE gets this
> benefit only because it is an overlay approach; the issue occurs where ever > the overlay ends. If one is doing 1 or 2-hop tunnels, then looping is also
> possible.

There is still no possibility of routing loops in multiarea TE.
For the traffic in the full overlay.

Actually it is a benefit of source specified forwarding.  So something
like NIMROD would have the same benefit even though it is
significantly different from MPLS RSVP/TE.  NIMROD is not an overlay.
Sure. But this works only for the region where the traffic is following
source specified forwarding; as soon as there's a local decision, it's back
to the possibility of loops.
Again - terminology.  Uncorrelated failures would be ones that don't
happen at the sake time.  I still got what you said.

Yes the tradeoff is probably worth it.  The point that I was trying to
make is you *can't* loop with MPLS/TE and you *can* loop with IP even
without IP FRR.  Looping is really bad since you affect other triaffic
if you congest links going around long enough for TTL to expire.
Any time you go back to hop-by-hop forwarding, you can loop. The only way
that MPLS/TE avoids it is with a full overlay.
Alia


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