subnet prefix length > 64 breaks IPv6?

Ryan Malayter malayter at
Wed Dec 28 11:51:18 CST 2011

On Dec 28, 9:44 am, Ray Soucy <r... at> 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"?

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