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Re: subnet prefix length > 64 breaks IPv6?
From: Ray Soucy <rps () maine edu>
Date: Wed, 28 Dec 2011 14:14:14 -0500

I did look into this a bit before.

To be more specific:

IPv6 CEF appears to be functioning normally for prefixes longer than
64-bit on my 720(s).

I'm not seeing evidence of unexpected punting.

The CPU utilization of the software process that would handle IPv6
being punted to software, "IPv6 Input", is at a steady %0.00 average
(with spikes up to 0.02%).

So there would seem to be at least one major platform that is OK.

On Wed, Dec 28, 2011 at 12:51 PM, Ryan Malayter <malayter () gmail com> wrote:

On Dec 28, 9:44 am, Ray Soucy <r... () maine edu> wrote:
For what its worth I haven't stress tested it or anything, but I
haven't seen any evidence on any of our RSP/SUP 720 boxes that would
have caused me to think that routing and forwarding isn't being done
in hardware, and we make liberal use of prefixes longer than 64
(including 126 for every link network).  They might just be under
capacity to the point that I haven't noticed, though.  I have no
problem getting muti-gigabit IPv6 throughput.

You can get >10GbE *throughput* from a Linux box doing all forwarding
in software as well. That's easy when the packets are big and the
routing tables are small, and the hash tables all fit in high-speed
processor cache.

The general lack of deep information about how the switching and
routing hardware really works for IPv6 is my main problem. It's not
enough to make informed buying or design decisions. Unfortunately, I
have over the course of my career learned that a "trust but verify"
policy is required when managing vendors. Especially vendors that have
a near-monopoly market position.

The problem, of course, is that verifying this sort of thing with
realistic worst-case benchmarks requires some very expensive equipment
and a lot of time, which is why the lack of solid information from
vendors and 3rd-party testing labs is worrying.

Surely some engineers from the major switch/router vendors read the
NANOG list. Anybody care to chime in with "we forward all IPv6 prefix
lengths in hardware for these product families"?

Ray Soucy

Epic Communications Specialist

Phone: +1 (207) 561-3526

Networkmaine, a Unit of the University of Maine System

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