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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: Thu, 25 Nov 2004 00:35:27 -0500
Hi Naiming,

At 02:02 AM 11/24/2004, Naiming Shen wrote:
yes, it's regardless of the number of LSPs for each LSP switch-over,
but the total switch-over time is linear to the number of LSPs affected.
The total switch-over time doesn't have to be linear with the number of
LSPs affected. It's certainly possible to design a fast path where this
isn't the case. I even think it is highly desirable (seen through the
focused glare of fast-reroute technologies).
yes, indirection makes it scalable. but a hardware design or an
existing forwarding engine may not want to do indirection due to
extra processing at forwarding time.
As I mentioned elsewhere, this is very hardware dependent. It doesn't have
to be extra processing and it saves on FIB memory.
Second, if node protection is desired, then it is necessary, in NFRR as in any of the tunneling schemes, to track the next-next-hop for each route or IGP destination. In that case, you need to organize indirection of routes to primary & alternate based upon the next-next-hop. NFRR provides no added benefit that I can see here. If one has the ability to add that extra level of indirecton (desirable anyway for fast IGP convergence), then that level can be added in to handle any of these IPFRR schemes.
For the hardware can do indirection of adjacencies, you are right,
that's not a big problem. But even that, NFRR is only concerned about
a couple of next-nexthop adjacencies and the traffic is for sure
being switched over to the next-nexthop nodes. For non-nexthop schemes,
I guess one needs to worry about BGP nexthops which are IGP nodes,
and next-nexthops of those IGP routes, so there is more complexities
to figure out those alternative indirections. And in the case of
inter-area node-protection of ABR router, this will be rather tricky.
These are the multi-homed prefix cases. Mike and Stewart have a good
discussion of them (even slanted towards tunnels oddly enough ;-) in their
draft. It's a bit of added complexity, but not too bad.
Alia


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